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    Command:

    bash

    
    
    

    SYNOPSIS

           bash [options] [file]
    
    
    

    COPYRIGHT

           Bash is Copyright (C) 1989-2009 by the Free Software Foundation, Inc.
    
    
    

    DESCRIPTION

           Bash  is  an  sh-compatible  command language interpreter that executes
           commands read from the standard input or from a file.  Bash also incor-
           porates useful features from the Korn and C shells (ksh and csh).
    
           Bash  is  intended  to  be a conformant implementation of the Shell and
           Utilities portion  of  the  IEEE  POSIX  specification  (IEEE  Standard
           1003.1).  Bash can be configured to be POSIX-conformant by default.
    
    
    

    OPTIONS

           In  addition  to  the  single-character shell options documented in the
           description of the set builtin command, bash interprets  the  following
           options when it is invoked:
    
           -c string If  the  -c  option  is  present, then commands are read from
                     string.  If there are arguments after the  string,  they  are
                     assigned to the positional parameters, starting with $0.
           -i        If the -i option is present, the shell is interactive.
           -l        Make bash act as if it had been invoked as a login shell (see
                     INVOCATION below).
           -r        If the -r option is present,  the  shell  becomes  restricted
                     (see RESTRICTED SHELL below).
           -s        If  the -s option is present, or if no arguments remain after
                     option processing, then commands are read from  the  standard
                     input.   This  option  allows the positional parameters to be
                     set when invoking an interactive shell.
           -D        A list of all double-quoted strings preceded by $ is  printed
                     on  the standard output.  These are the strings that are sub-
                     ject to language translation when the current locale is not C
                     or  POSIX.   This  implies the -n option; no commands will be
                     executed.
           [-+]O [shopt_option]
                     shopt_option is one of the  shell  options  accepted  by  the
                     shopt   builtin  (see  SHELL  BUILTIN  COMMANDS  below).   If
                     shopt_option is present, -O sets the value of that option; +O
                     unsets  it.   If  shopt_option is not supplied, the names and
                     values of the shell options accepted by shopt are printed  on
                     the  standard  output.   If  the invocation option is +O, the
                     output is displayed in a format that may be reused as  input.
           --        A  --  signals the end of options and disables further option
                     processing.  Any arguments after the -- are treated as  file-
                     names and arguments.  An argument of - is equivalent to --.
    
           Bash  also  interprets  a  number  of  multi-character  options.  These
           options must appear on the command  line  before  the  single-character
           options to be recognized.
           --init-file file
           --rcfile file
                  Execute commands from file instead of the standard personal ini-
                  tialization file ~/.bashrc if  the  shell  is  interactive  (see
                  INVOCATION below).
    
           --login
                  Equivalent to -l.
    
           --noediting
                  Do  not  use the GNU readline library to read command lines when
                  the shell is interactive.
    
           --noprofile
                  Do not read either the system-wide startup file /etc/profile  or
                  any   of  the  personal  initialization  files  ~/.bash_profile,
                  ~/.bash_login, or ~/.profile.   By  default,  bash  reads  these
                  files  when  it  is  invoked  as  a  login shell (see INVOCATION
                  below).
    
           --norc Do  not  read  and  execute  the  personal  initialization  file
                  ~/.bashrc  if  the  shell  is interactive.  This option is on by
                  default if the shell is invoked as sh.
    
           --posix
                  Change the behavior of bash where the default operation  differs
                  from the POSIX standard to match the standard (posix mode).
    
           --restricted
                  The shell becomes restricted (see RESTRICTED SHELL below).
    
           --rpm-requires
                  Produce the list of files that are required for the shell script
                  to run.  This implies '-n' and is subject to  the  same  limita-
                  tions  as  compile  time  error checking checking; Backticks, []
                  tests,  and evals are not parsed so  some  dependencies  may  be
                  missed.
    
           --verbose
                  Equivalent to  -v.
    
           --version
                  Show  version information for this instance of bash on the stan-
                  dard output and exit successfully.
    
    
    

    ARGUMENTS

           If arguments remain after option processing, and neither the -c nor the
           -s  option  has  been supplied, the first argument is assumed to be the
           name of a file containing shell commands.  If bash is invoked  in  this
           fashion,  $0 is set to the name of the file, and the positional parame-
           ters are set to the remaining arguments.  Bash reads and executes  com-
           mands  from this file, then exits.  Bash's exit status is the exit sta-
    
           The following paragraphs describe how bash executes its startup  files.
           If  any  of  the files exist but cannot be read, bash reports an error.
           Tildes are expanded in file names as described below under Tilde Expan-
           sion in the EXPANSION section.
    
           When  bash is invoked as an interactive login shell, or as a non-inter-
           active shell with the --login option, it first reads and executes  com-
           mands  from  the file /etc/profile, if that file exists.  After reading
           that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile,
           in  that order, and reads and executes commands from the first one that
           exists and is readable.  The --noprofile option may be  used  when  the
           shell is started to inhibit this behavior.
    
           When  a  login  shell  exits, bash reads and executes commands from the
           files ~/.bash_logout and /etc/bash.bash_logout, if the files exists.
    
           When an interactive shell that is not a login shell  is  started,  bash
           reads  and executes commands from ~/.bashrc, if that file exists.  This
           may be inhibited by using the --norc option.  The --rcfile file  option
           will  force  bash  to  read  and  execute commands from file instead of
           ~/.bashrc.
    
           When bash is started non-interactively, to  run  a  shell  script,  for
           example, it looks for the variable BASH_ENV in the environment, expands
           its value if it appears there, and uses the expanded value as the  name
           of  a  file to read and execute.  Bash behaves as if the following com-
           mand were executed:
                  if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
           but the value of the PATH variable is not used to search for  the  file
           name.
    
           If  bash  is  invoked  with  the name sh, it tries to mimic the startup
           behavior of historical versions of sh as  closely  as  possible,  while
           conforming  to the POSIX standard as well.  When invoked as an interac-
           tive login shell, or a non-interactive shell with the  --login  option,
           it  first  attempts  to read and execute commands from /etc/profile and
           ~/.profile, in that order.  The  --noprofile  option  may  be  used  to
           inhibit  this  behavior.  When invoked as an interactive shell with the
           name sh, bash looks for the variable ENV, expands its value  if  it  is
           defined,  and uses the expanded value as the name of a file to read and
           execute.  Since a shell invoked as sh does not attempt to read and exe-
           cute  commands from any other startup files, the --rcfile option has no
           effect.  A non-interactive shell invoked with  the  name  sh  does  not
           attempt  to  read  any  other  startup files.  When invoked as sh, bash
           enters posix mode after the startup files are read.
    
           When bash is started in posix mode, as with the  --posix  command  line
           option, it follows the POSIX standard for startup files.  In this mode,
           interactive shells expand the ENV variable and commands  are  read  and
           executed  from  the  file  whose  name is the expanded value.  No other
           startup files are read.
           the  SHELLOPTS,  BASHOPTS,  CDPATH,  and  GLOBIGNORE variables, if they
           appear in the environment, are ignored, and the effective  user  id  is
           set  to  the real user id.  If the -p option is supplied at invocation,
           the startup behavior is the same, but the  effective  user  id  is  not
           reset.
    
    
    

    DEFINITIONS

           The  following  definitions  are used throughout the rest of this docu-
           ment.
           blank  A space or tab.
           word   A sequence of characters considered as  a  single  unit  by  the
                  shell.  Also known as a token.
           name   A  word  consisting  only  of alphanumeric characters and under-
                  scores, and beginning with an alphabetic character or an  under-
                  score.  Also referred to as an identifier.
           metacharacter
                  A  character  that,  when unquoted, separates words.  One of the
                  following:
                  |  & ; ( ) < > space tab
           control operator
                  A token that performs a control function.  It is one of the fol-
                  lowing symbols:
                  || & && ; ;; ( ) | |& <newline>
    
    
    

    RESERVED WORDS

           Reserved words are words that have a special meaning to the shell.  The
           following words are recognized as reserved when unquoted and either the
           first  word  of a simple command (see SHELL GRAMMAR below) or the third
           word of a case or for command:
    
           ! case  do done elif else esac fi for function if in select then  until
           while { } time [[ ]]
    
    
    

    SHELL GRAMMAR

       Simple Commands
           A  simple  command  is a sequence of optional variable assignments fol-
           lowed by blank-separated words and redirections, and  terminated  by  a
           control operator.  The first word specifies the command to be executed,
           and is passed as argument zero.  The  remaining  words  are  passed  as
           arguments to the invoked command.
    
           The  return  value  of a simple command is its exit status, or 128+n if
           the command is terminated by signal n.
    
       Pipelines
           A pipeline is a sequence of one or more commands separated  by  one  of
           the control operators | or |&.  The format for a pipeline is:
    
                  [time [-p]] [ ! ] command [ [|||&] command2 ... ]
    
           The  standard output of command is connected via a pipe to the standard
           input of command2.  This connection is performed  before  any  redirec-
    
           If the time reserved word precedes a pipeline, the elapsed as  well  as
           user  and  system  time consumed by its execution are reported when the
           pipeline terminates.  The -p option changes the output format  to  that
           specified  by  POSIX.   The  TIMEFORMAT variable may be set to a format
           string that specifies how the timing information should  be  displayed;
           see the description of TIMEFORMAT under Shell Variables below.
    
           Each  command in a pipeline is executed as a separate process (i.e., in
           a subshell).
    
       Lists
           A list is a sequence of one or more pipelines separated by one  of  the
           operators ;, &, &&, or ||, and optionally terminated by one of ;, &, or
           <newline>.
    
           Of these list operators, && and || have equal precedence, followed by ;
           and &, which have equal precedence.
    
           A  sequence  of  one or more newlines may appear in a list instead of a
           semicolon to delimit commands.
    
           If a command is terminated by the control operator &,  the  shell  exe-
           cutes  the command in the background in a subshell.  The shell does not
           wait for the command to finish, and the return status is  0.   Commands
           separated  by  a  ; are executed sequentially; the shell waits for each
           command to terminate in turn.  The return status is the exit status  of
           the last command executed.
    
           AND  and  OR  lists are sequences of one of more pipelines separated by
           the && and || control operators, respectively.  AND and  OR  lists  are
           executed with left associativity.  An AND list has the form
    
                  command1 && command2
    
           command2  is  executed if, and only if, command1 returns an exit status
           of zero.
    
           An OR list has the form
    
                  command1 || command2
    
           command2 is executed if and only if command1 returns  a  non-zero  exit
           status.   The  return  status of AND and OR lists is the exit status of
           the last command executed in the list.
    
       Compound Commands
           A compound command is one of the following:
    
           (list) list is executed in a subshell environment (see  COMMAND  EXECU-
                  TION  ENVIRONMENT below).  Variable assignments and builtin com-
    
           ((expression))
                  The  expression  is  evaluated  according to the rules described
                  below under ARITHMETIC EVALUATION.  If the value of the  expres-
                  sion  is  non-zero, the return status is 0; otherwise the return
                  status is 1.  This is exactly equivalent to let "expression".
    
           [[ expression ]]
                  Return a status of 0 or 1 depending on  the  evaluation  of  the
                  conditional  expression expression.  Expressions are composed of
                  the primaries described  below  under  CONDITIONAL  EXPRESSIONS.
                  Word  splitting  and pathname expansion are not performed on the
                  words between the [[ and  ]];  tilde  expansion,  parameter  and
                  variable  expansion, arithmetic expansion, command substitution,
                  process substitution, and quote removal are  performed.   Condi-
                  tional operators such as -f must be unquoted to be recognized as
                  primaries.
    
                  When used with [[, The < and > operators sort  lexicographically
                  using the current locale.
    
                  When  the  == and != operators are used, the string to the right
                  of the operator is considered a pattern and matched according to
                  the  rules described below under Pattern Matching.  If the shell
                  option nocasematch is enabled, the match  is  performed  without
                  regard  to  the case of alphabetic characters.  The return value
                  is 0 if the string matches (==) or does not match (!=) the  pat-
                  tern, and 1 otherwise.  Any part of the pattern may be quoted to
                  force it to be matched as a string.
    
                  An additional binary operator, =~, is available, with  the  same
                  precedence  as  ==  and  !=.  When it is used, the string to the
                  right of the operator is considered an extended regular  expres-
                  sion and matched accordingly (as in regex(3)).  The return value
                  is 0 if the string matches the pattern, and 1 otherwise.  If the
                  regular  expression  is syntactically incorrect, the conditional
                  expression's return value is 2.  If the shell option nocasematch
                  is enabled, the match is performed without regard to the case of
                  alphabetic characters.  Any part of the pattern may be quoted to
                  force  it  to  be  matched  as  a string.  Substrings matched by
                  parenthesized subexpressions within the regular  expression  are
                  saved  in  the  array  variable  BASH_REMATCH.   The  element of
                  BASH_REMATCH with index 0 is the portion of the string  matching
                  the entire regular expression.  The element of BASH_REMATCH with
                  index n is the portion of the string matching the nth  parenthe-
                  sized subexpression.
    
                  Expressions  may  be  combined  using  the  following operators,
                  listed in decreasing order of precedence:
    
                  ( expression )
                         Returns the value of expression.  This  may  be  used  to
                         override the normal precedence of operators.
    
                  turn,  and  list is executed each time.  If the in word is omit-
                  ted, the for command executes  list  once  for  each  positional
                  parameter that is set (see PARAMETERS below).  The return status
                  is the exit status of the last command that  executes.   If  the
                  expansion of the items following in results in an empty list, no
                  commands are executed, and the return status is 0.
    
           for (( expr1 ; expr2 ; expr3 )) ; do list ; done
                  First, the arithmetic expression expr1 is evaluated according to
                  the  rules  described  below  under  ARITHMETIC EVALUATION.  The
                  arithmetic expression expr2 is then evaluated  repeatedly  until
                  it  evaluates  to zero.  Each time expr2 evaluates to a non-zero
                  value, list is executed and the arithmetic expression  expr3  is
                  evaluated.   If  any  expression is omitted, it behaves as if it
                  evaluates to 1.  The return value is the exit status of the last
                  command in list that is executed, or false if any of the expres-
                  sions is invalid.
    
           select name [ in word ] ; do list ; done
                  The list of words following in is expanded, generating a list of
                  items.   The  set  of  expanded words is printed on the standard
                  error, each preceded by a number.  If the in  word  is  omitted,
                  the  positional  parameters  are printed (see PARAMETERS below).
                  The PS3 prompt is then displayed and a line read from the  stan-
                  dard  input.   If the line consists of a number corresponding to
                  one of the displayed words, then the value of  name  is  set  to
                  that  word.  If the line is empty, the words and prompt are dis-
                  played again.  If EOF is read, the command completes.  Any other
                  value  read  causes  name  to  be set to null.  The line read is
                  saved in the variable REPLY.  The list is  executed  after  each
                  selection until a break command is executed.  The exit status of
                  select is the exit status of the last command executed in  list,
                  or zero if no commands were executed.
    
           case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
                  A case command first expands word, and tries to match it against
                  each pattern in turn, using the same matching rules as for path-
                  name  expansion  (see  Pathname  Expansion  below).  The word is
                  expanded using tilde expansion, parameter  and  variable  expan-
                  sion,  arithmetic  substitution,  command  substitution, process
                  substitution  and  quote  removal.   Each  pattern  examined  is
                  expanded  using  tilde  expansion, parameter and variable expan-
                  sion, arithmetic substitution, command substitution, and process
                  substitution.   If  the shell option nocasematch is enabled, the
                  match is performed without regard  to  the  case  of  alphabetic
                  characters.   When  a  match is found, the corresponding list is
                  executed.  If the ;; operator is used, no subsequent matches are
                  attempted  after  the first pattern match.  Using ;& in place of
                  ;; causes execution to continue with the  list  associated  with
                  the  next  set of patterns.  Using ;;& in place of ;; causes the
                  shell to test the next pattern list in the  statement,  if  any,
                  and execute any associated list on a successful match.  The exit
                  The  while  command continuously executes the do list as long as
                  the last command in list returns an exit status  of  zero.   The
                  until command is identical to the while command, except that the
                  test is negated; the do list is executed as  long  as  the  last
                  command in list returns a non-zero exit status.  The exit status
                  of the while and until commands is the exit status of  the  last
                  do list command executed, or zero if none was executed.
    
       Coprocesses
           A coprocess is a shell command preceded by the coproc reserved word.  A
           coprocess is executed asynchronously in a subshell, as if  the  command
           had  been  terminated  with the & control operator, with a two-way pipe
           established between the executing shell and the coprocess.
    
           The format for a coprocess is:
    
                  coproc [NAME] command [redirections]
    
           This creates a coprocess named NAME.  If  NAME  is  not  supplied,  the
           default name is COPROC.  NAME must not be supplied if command is a sim-
           ple command (see above); otherwise, it is interpreted as the first word
           of  the simple command.  When the coproc is executed, the shell creates
           an array variable (see Arrays below) named NAME in the context  of  the
           executing  shell.   The  standard  output of command is connected via a
           pipe to a file  descriptor  in  the  executing  shell,  and  that  file
           descriptor  is  assigned  to NAME[0].  The standard input of command is
           connected via a pipe to a file descriptor in the executing  shell,  and
           that  file descriptor is assigned to NAME[1].  This pipe is established
           before any redirections  specified  by  the  command  (see  REDIRECTION
           below).   The  file  descriptors  can be utilized as arguments to shell
           commands and redirections using standard word expansions.  The  process
           id  of  the  shell spawned to execute the coprocess is available as the
           value of the variable NAME_PID.  The wait builtin command may  be  used
           to wait for the coprocess to terminate.
    
           The return status of a coprocess is the exit status of command.
    
       Shell Function Definitions
           A  shell function is an object that is called like a simple command and
           executes a compound command with a new set  of  positional  parameters.
           Shell functions are declared as follows:
    
           [ function ] name () compound-command [redirection]
                  This  defines a function named name.  The reserved word function
                  is optional.  If the function reserved  word  is  supplied,  the
                  parentheses  are optional.  The body of the function is the com-
                  pound command compound-command (see  Compound  Commands  above).
                  That  command is usually a list of commands between { and }, but
                  may be any command listed under Compound Commands  above.   com-
                  pound-command is executed whenever name is specified as the name
                  of a simple command.  Any redirections (see  REDIRECTION  below)
                  specified  when  a  function  is  defined are performed when the
    
    
    

    QUOTING

           Quoting is used to remove the special meaning of certain characters  or
           words  to  the shell.  Quoting can be used to disable special treatment
           for special characters, to prevent reserved words from being recognized
           as such, and to prevent parameter expansion.
    
           Each  of  the metacharacters listed above under DEFINITIONS has special
           meaning to the shell and must be quoted if it is to represent itself.
    
           When the command history expansion facilities are being used (see  HIS-
           TORY EXPANSION below), the history expansion character, usually !, must
           be quoted to prevent history expansion.
    
           There are  three  quoting  mechanisms:  the  escape  character,  single
           quotes, and double quotes.
    
           A  non-quoted  backslash (\) is the escape character.  It preserves the
           literal value of the next character that follows, with the exception of
           <newline>.   If  a  \<newline>  pair  appears, and the backslash is not
           itself quoted, the \<newline> is treated as a line  continuation  (that
           is, it is removed from the input stream and effectively ignored).
    
           Enclosing  characters  in  single quotes preserves the literal value of
           each character within the quotes.  A single quote may not occur between
           single quotes, even when preceded by a backslash.
    
           Enclosing  characters  in  double quotes preserves the literal value of
           all characters within the quotes, with the exception of $, `,  \,  and,
           when  history  expansion  is enabled, !.  The characters $ and ` retain
           their special meaning within double quotes.  The backslash retains  its
           special  meaning only when followed by one of the following characters:
           $, `, ", \, or <newline>.  A double quote may be quoted  within  double
           quotes by preceding it with a backslash.  If enabled, history expansion
           will be performed unless an !  appearing in double  quotes  is  escaped
           using a backslash.  The backslash preceding the !  is not removed.
    
           The  special  parameters  *  and  @ have special meaning when in double
           quotes (see PARAMETERS below).
    
           Words of the form $'string' are treated specially.  The word expands to
           string,  with backslash-escaped characters replaced as specified by the
           ANSI C standard.  Backslash escape sequences, if present,  are  decoded
           as follows:
                  \a     alert (bell)
                  \b     backspace
                  \e
                  \E     an escape character
                  \f     form feed
                  \n     new line
                  \r     carriage return
                  \t     horizontal tab
    
           the  string  to  be translated according to the current locale.  If the
           current locale is C or POSIX, the  dollar  sign  is  ignored.   If  the
           string is translated and replaced, the replacement is double-quoted.
    
    
    

    PARAMETERS

           A  parameter is an entity that stores values.  It can be a name, a num-
           ber, or one of the special characters listed below under Special Param-
           eters.   A variable is a parameter denoted by a name.  A variable has a
           value and zero or more attributes.  Attributes are assigned  using  the
           declare  builtin command (see declare below in SHELL BUILTIN COMMANDS).
    
           A parameter is set if it has been assigned a value.  The null string is
           a  valid  value.  Once a variable is set, it may be unset only by using
           the unset builtin command (see SHELL BUILTIN COMMANDS below).
    
           A variable may be assigned to by a statement of the form
    
                  name=[value]
    
           If value is not given, the variable is assigned the null  string.   All
           values  undergo tilde expansion, parameter and variable expansion, com-
           mand substitution, arithmetic expansion, and quote removal (see  EXPAN-
           SION below).  If the variable has its integer attribute set, then value
           is evaluated as an arithmetic expression even if the $((...)) expansion
           is  not  used  (see Arithmetic Expansion below).  Word splitting is not
           performed, with the exception of "$@" as explained below under  Special
           Parameters.   Pathname  expansion  is not performed.  Assignment state-
           ments may also appear as arguments  to  the  alias,  declare,  typeset,
           export, readonly, and local builtin commands.
    
           In  the context where an assignment statement is assigning a value to a
           shell variable or array index, the += operator can be used to append to
           or add to the variable's previous value.  When += is applied to a vari-
           able for which the integer attribute has been set, value  is  evaluated
           as  an arithmetic expression and added to the variable's current value,
           which is also evaluated.  When += is applied to an array variable using
           compound  assignment  (see  Arrays  below), the variable's value is not
           unset (as it is when using =), and new values are appended to the array
           beginning  at  one  greater than the array's maximum index (for indexed
           arrays) or added as additional key-value pairs in an associative array.
           When  applied  to  a  string-valued  variable,  value  is  expanded and
           appended to the variable's value.
    
       Positional Parameters
           A positional parameter is a parameter denoted by one  or  more  digits,
           other than the single digit 0.  Positional parameters are assigned from
           the shell's arguments when it is invoked, and may be  reassigned  using
           the  set builtin command.  Positional parameters may not be assigned to
           with assignment statements.  The positional parameters are  temporarily
           replaced when a shell function is executed (see FUNCTIONS below).
    
           When  a  positional parameter consisting of more than a single digit is
                  the  expansion  occurs  within  double  quotes,  each  parameter
                  expands to a separate word.  That is, "$@" is equivalent to "$1"
                  "$2"  ...   If the double-quoted expansion occurs within a word,
                  the expansion of the first parameter is joined with  the  begin-
                  ning  part  of  the original word, and the expansion of the last
                  parameter is joined with the last part  of  the  original  word.
                  When  there  are no positional parameters, "$@" and $@ expand to
                  nothing (i.e., they are removed).
           #      Expands to the number of positional parameters in decimal.
           ?      Expands to the exit status of the most recently  executed  fore-
                  ground pipeline.
           -      Expands  to  the  current option flags as specified upon invoca-
                  tion, by the set builtin command, or  those  set  by  the  shell
                  itself (such as the -i option).
           $      Expands  to  the  process ID of the shell.  In a () subshell, it
                  expands to the process ID of the current  shell,  not  the  sub-
                  shell.
           !      Expands  to  the  process ID of the most recently executed back-
                  ground (asynchronous) command.
           0      Expands to the name of the shell or shell script.  This  is  set
                  at shell initialization.  If bash is invoked with a file of com-
                  mands, $0 is set to the name of that file.  If bash  is  started
                  with  the  -c option, then $0 is set to the first argument after
                  the string to be executed, if one is present.  Otherwise, it  is
                  set  to  the file name used to invoke bash, as given by argument
                  zero.
           _      At shell startup, set to the absolute pathname  used  to  invoke
                  the  shell or shell script being executed as passed in the envi-
                  ronment or argument list.  Subsequently,  expands  to  the  last
                  argument  to the previous command, after expansion.  Also set to
                  the full pathname used  to  invoke  each  command  executed  and
                  placed in the environment exported to that command.  When check-
                  ing mail, this parameter holds the name of the  mail  file  cur-
                  rently being checked.
    
       Shell Variables
           The following variables are set by the shell:
    
           BASH   Expands  to  the  full file name used to invoke this instance of
                  bash.
           BASHOPTS
                  A colon-separated list of enabled shell options.  Each  word  in
                  the  list  is  a  valid  argument for the -s option to the shopt
                  builtin command (see SHELL BUILTIN COMMANDS below).  The options
                  appearing  in  BASHOPTS  are  those reported as on by shopt.  If
                  this variable is in the environment when bash  starts  up,  each
                  shell  option  in  the  list  will be enabled before reading any
                  startup files.  This variable is read-only.
           BASHPID
                  Expands to the process id of the  current  bash  process.   This
                  differs  from  $$ under certain circumstances, such as subshells
                  that do not require bash to be re-initialized.
    
           BASH_ARGV
                  An  array  variable containing all of the parameters in the cur-
                  rent bash execution call stack.  The final parameter of the last
                  subroutine  call is at the top of the stack; the first parameter
                  of the initial call is at the bottom.  When a subroutine is exe-
                  cuted,  the  parameters supplied are pushed onto BASH_ARGV.  The
                  shell sets BASH_ARGV only when in extended debugging  mode  (see
                  the  description  of  the  extdebug  option to the shopt builtin
                  below)
           BASH_CMDS
                  An associative array variable whose members  correspond  to  the
                  internal  hash  table  of  commands  as  maintained  by the hash
                  builtin.  Elements added to this array appear in the hash table;
                  unsetting  array  elements cause commands to be removed from the
                  hash table.
           BASH_COMMAND
                  The command currently being executed or about  to  be  executed,
                  unless the shell is executing a command as the result of a trap,
                  in which case it is the command executing at  the  time  of  the
                  trap.
           BASH_EXECUTION_STRING
                  The command argument to the -c invocation option.
           BASH_LINENO
                  An  array  variable whose members are the line numbers in source
                  files   corresponding    to    each    member    of    FUNCNAME.
                  ${BASH_LINENO[$i]}  is  the line number in the source file where
                  ${FUNCNAME[$i]} was called (or  ${BASH_LINENO[$i-1]}  if  refer-
                  enced  within another shell function).  The corresponding source
                  file name is ${BASH_SOURCE[$i]}.  Use LINENO to obtain the  cur-
                  rent line number.
           BASH_REMATCH
                  An  array  variable  whose members are assigned by the =~ binary
                  operator to the [[ conditional command.  The element with  index
                  0  is  the  portion  of  the  string matching the entire regular
                  expression.  The element with index n  is  the  portion  of  the
                  string matching the nth parenthesized subexpression.  This vari-
                  able is read-only.
           BASH_SOURCE
                  An array variable whose members are the source filenames  corre-
                  sponding to the elements in the FUNCNAME array variable.
           BASH_SUBSHELL
                  Incremented  by one each time a subshell or subshell environment
                  is spawned.  The initial value is 0.
           BASH_VERSINFO
                  A readonly array variable whose members hold version information
                  for  this  instance  of  bash.  The values assigned to the array
                  members are as follows:
                  BASH_VERSINFO[0]        The major version number (the  release).
                  BASH_VERSINFO[1]        The  minor version number (the version).
                  BASH_VERSINFO[2]        The patch level.
                  BASH_VERSINFO[3]        The build version.
                  BASH_VERSINFO[4]        The release status (e.g., beta1).
                  rent completion function.
    
           COMP_LINE
                  The  current  command  line.  This variable is available only in
                  shell functions  and  external  commands  invoked  by  the  pro-
                  grammable  completion  facilities  (see  Programmable Completion
                  below).
    
           COMP_POINT
                  The index of the current cursor position relative to the  begin-
                  ning  of the current command.  If the current cursor position is
                  at the end of the current command, the value of this variable is
                  equal  to  ${#COMP_LINE}.   This  variable  is available only in
                  shell functions  and  external  commands  invoked  by  the  pro-
                  grammable  completion  facilities  (see  Programmable Completion
                  below).
    
           COMP_TYPE
                  Set to an integer value corresponding to the type of  completion
                  attempted  that  caused a completion function to be called: TAB,
                  for normal completion, ?, for listing completions after  succes-
                  sive  tabs,  !, for listing alternatives on partial word comple-
                  tion, @, to list completions if the word is not  unmodified,  or
                  %,  for  menu  completion.   This  variable is available only in
                  shell functions  and  external  commands  invoked  by  the  pro-
                  grammable  completion  facilities  (see  Programmable Completion
                  below).
    
           COMP_WORDBREAKS
                  The set of characters that the readline library treats  as  word
                  separators  when performing word completion.  If COMP_WORDBREAKS
                  is unset, it loses its special properties, even if it is  subse-
                  quently reset.
    
           COMP_WORDS
                  An  array variable (see Arrays below) consisting of the individ-
                  ual words in the current command line.  The line is  split  into
                  words  as  readline  would  split  it,  using COMP_WORDBREAKS as
                  described above.  This variable is available only in shell func-
                  tions  invoked  by  the  programmable completion facilities (see
                  Programmable Completion below).
    
           DIRSTACK
                  An array variable (see Arrays below) containing the current con-
                  tents  of  the directory stack.  Directories appear in the stack
                  in the order they are displayed by the dirs builtin.   Assigning
                  to members of this array variable may be used to modify directo-
                  ries already in the stack, but the pushd and popd builtins  must
                  be used to add and remove directories.  Assignment to this vari-
                  able will not change the  current  directory.   If  DIRSTACK  is
                  unset,  it  loses  its  special properties, even if it is subse-
                  quently reset.
                  current  user is a member.  Assignments to GROUPS have no effect
                  and return an error status.  If GROUPS is unset,  it  loses  its
                  special properties, even if it is subsequently reset.
    
           HISTCMD
                  The history number, or index in the history list, of the current
                  command.  If HISTCMD is unset, it loses its special  properties,
                  even if it is subsequently reset.
    
           HOSTNAME
                  Automatically set to the name of the current host.
    
           HOSTTYPE
                  Automatically  set  to a string that uniquely describes the type
                  of machine on which bash is executing.  The default  is  system-
                  dependent.
    
           LINENO Each  time this parameter is referenced, the shell substitutes a
                  decimal number representing the current sequential  line  number
                  (starting  with  1)  within a script or function.  When not in a
                  script or function, the value substituted is not  guaranteed  to
                  be meaningful.  If LINENO is unset, it loses its special proper-
                  ties, even if it is subsequently reset.
    
           MACHTYPE
                  Automatically set to a string that fully  describes  the  system
                  type  on  which  bash is executing, in the standard GNU cpu-com-
                  pany-system format.  The default is system-dependent.
    
           OLDPWD The previous working directory as set by the cd command.
    
           OPTARG The value of the last option argument processed by  the  getopts
                  builtin command (see SHELL BUILTIN COMMANDS below).
    
           OPTIND The  index  of  the next argument to be processed by the getopts
                  builtin command (see SHELL BUILTIN COMMANDS below).
    
           OSTYPE Automatically set to a string that describes the operating  sys-
                  tem  on  which  bash is executing.  The default is system-depen-
                  dent.
    
           PIPESTATUS
                  An array variable (see Arrays below) containing a list  of  exit
                  status  values  from the processes in the most-recently-executed
                  foreground pipeline (which may contain only a single command).
    
           PPID   The process ID of the shell's parent.  This  variable  is  read-
                  only.
    
           PWD    The current working directory as set by the cd command.
    
           RANDOM Each time this parameter is referenced, a random integer between
                  is subsequently reset.
    
           SHELLOPTS
                  A  colon-separated  list of enabled shell options.  Each word in
                  the list is a valid argument  for  the  -o  option  to  the  set
                  builtin command (see SHELL BUILTIN COMMANDS below).  The options
                  appearing in SHELLOPTS are those reported as on by set  -o.   If
                  this  variable  is  in the environment when bash starts up, each
                  shell option in the list will  be  enabled  before  reading  any
                  startup files.  This variable is read-only.
    
           SHLVL  Incremented by one each time an instance of bash is started.
    
           UID    Expands to the user ID of the current user, initialized at shell
                  startup.  This variable is readonly.
    
           The following variables are used by the shell.   In  some  cases,  bash
           assigns a default value to a variable; these cases are noted below.
    
           BASH_ENV
                  If  this parameter is set when bash is executing a shell script,
                  its value is interpreted as a filename  containing  commands  to
                  initialize the shell, as in ~/.bashrc.  The value of BASH_ENV is
                  subjected to  parameter  expansion,  command  substitution,  and
                  arithmetic  expansion  before  being interpreted as a file name.
                  PATH is not used to search for the resultant file name.
           CDPATH The search path for the cd command.  This is  a  colon-separated
                  list  of  directories  in  which the shell looks for destination
                  directories specified by the cd  command.   A  sample  value  is
                  ".:~:/usr".
           BASH_XTRACEFD
                  If  set  to an integer corresponding to a valid file descriptor,
                  bash will write the  trace  output  generated  when  set  -x  is
                  enabled  to that file descriptor.  The file descriptor is closed
                  when BASH_XTRACEFD is unset or assigned a new value.   Unsetting
                  BASH_XTRACEFD  or assigning it the empty string causes the trace
                  output to be sent to the  standard  error.   Note  that  setting
                  BASH_XTRACEFD to 2 (the standard error file descriptor) and then
                  unsetting it will result in the standard error being closed.
           COLUMNS
                  Used by the select builtin command  to  determine  the  terminal
                  width  when  printing  selection  lists.  Automatically set upon
                  receipt of a SIGWINCH.
           COMPREPLY
                  An array variable from which bash reads the possible completions
                  generated  by  a shell function invoked by the programmable com-
                  pletion facility (see Programmable Completion below).
           EMACS  If bash finds this variable in the environment  when  the  shell
                  starts  with  value "t", it assumes that the shell is running in
                  an emacs shell buffer and disables line editing.
           FCEDIT The default editor for the fc builtin command.
           FIGNORE
                  matching the previous history entry to not be saved.  A value of
                  ignoreboth is shorthand for ignorespace and ignoredups.  A value
                  of erasedups causes all previous lines matching the current line
                  to  be  removed from the history list before that line is saved.
                  Any value not in the above list is ignored.  If  HISTCONTROL  is
                  unset,  or does not include a valid value, all lines read by the
                  shell parser are saved on the history list, subject to the value
                  of  HISTIGNORE.  The second and subsequent lines of a multi-line
                  compound command are not tested, and are added  to  the  history
                  regardless of the value of HISTCONTROL.
           HISTFILE
                  The name of the file in which command history is saved (see HIS-
                  TORY below).  The default value is ~/.bash_history.   If  unset,
                  the  command  history  is  not  saved  when an interactive shell
                  exits.
           HISTFILESIZE
                  The maximum number of lines contained in the history file.  When
                  this  variable  is  assigned  a value, the history file is trun-
                  cated, if necessary, by removing the oldest entries, to  contain
                  no  more  than  that number of lines.  The default value is 500.
                  The history file is also truncated to this size after writing it
                  when an interactive shell exits.
           HISTIGNORE
                  A  colon-separated list of patterns used to decide which command
                  lines should be saved on the  history  list.   Each  pattern  is
                  anchored  at  the  beginning of the line and must match the com-
                  plete line (no implicit  '*'  is  appended).   Each  pattern  is
                  tested  against  the line after the checks specified by HISTCON-
                  TROL are applied.  In  addition  to  the  normal  shell  pattern
                  matching characters, '&' matches the previous history line.  '&'
                  may be escaped using  a  backslash;  the  backslash  is  removed
                  before attempting a match.  The second and subsequent lines of a
                  multi-line compound command are not tested, and are added to the
                  history regardless of the value of HISTIGNORE.
           HISTSIZE
                  The  number  of commands to remember in the command history (see
                  HISTORY below).  The default value is 500.
           HISTTIMEFORMAT
                  If this variable is set and not null, its value  is  used  as  a
                  format string for strftime(3) to print the time stamp associated
                  with each history entry displayed by the  history  builtin.   If
                  this  variable  is  set,  time stamps are written to the history
                  file so they may be preserved across shell sessions.  This  uses
                  the  history  comment  character  to distinguish timestamps from
                  other history lines.
           HOME   The home directory of the current user; the default argument for
                  the cd builtin command.  The value of this variable is also used
                  when performing tilde expansion.
           HOSTFILE
                  Contains the name of a file in the  same  format  as  /etc/hosts
                  that should be read when the shell needs to complete a hostname.
                  The list of possible hostname completions may be  changed  while
                  characters on an input line before bash exits.  If the  variable
                  exists  but  does not have a numeric value, or has no value, the
                  default value is 10.  If it does not exist,  EOF  signifies  the
                  end of input to the shell.
           INPUTRC
                  The  filename  for  the  readline  startup  file, overriding the
                  default of ~/.inputrc (see READLINE below).
           LANG   Used to determine the  locale  category  for  any  category  not
                  specifically selected with a variable starting with LC_.
           LC_ALL This  variable  overrides  the  value  of LANG and any other LC_
                  variable specifying a locale category.
           LC_COLLATE
                  This variable determines the collation order used  when  sorting
                  the  results  of pathname expansion, and determines the behavior
                  of  range  expressions,  equivalence  classes,   and   collating
                  sequences within pathname expansion and pattern matching.
           LC_CTYPE
                  This  variable  determines  the interpretation of characters and
                  the behavior of character classes within pathname expansion  and
                  pattern matching.
           LC_MESSAGES
                  This  variable  determines  the locale used to translate double-
                  quoted strings preceded by a $.
           LC_NUMERIC
                  This variable determines the locale  category  used  for  number
                  formatting.
           LINES  Used  by  the  select  builtin  command  to determine the column
                  length for printing selection  lists.   Automatically  set  upon
                  receipt of a SIGWINCH.
           MAIL   If  this  parameter is set to a file name and the MAILPATH vari-
                  able is not set, bash informs the user of the arrival of mail in
                  the specified file.
           MAILCHECK
                  Specifies  how  often  (in  seconds)  bash checks for mail.  The
                  default is 60 seconds.  When it is time to check for  mail,  the
                  shell  does  so  before  displaying the primary prompt.  If this
                  variable is unset, or set to  a  value  that  is  not  a  number
                  greater than or equal to zero, the shell disables mail checking.
           MAILPATH
                  A colon-separated list of file names to  be  checked  for  mail.
                  The message to be printed when mail arrives in a particular file
                  may be specified by separating the file name  from  the  message
                  with a '?'.  When used in the text of the message, $_ expands to
                  the name of the current mailfile.  Example:
                  MAILPATH='/var/mail/bfox?"You  have  mail":~/shell-mail?"$_  has
                  mail!"'
                  Bash  supplies  a  default  value  for  this  variable,  but the
                  location of the user mail files that it uses is system dependent
                  (e.g., /var/mail/$USER).
           OPTERR If set to the value 1, bash displays error messages generated by
                  the getopts builtin command (see SHELL BUILTIN COMMANDS  below).
                  OPTERR  is  initialized to 1 each time the shell is invoked or a
                  command set -o posix had been executed.
           PROMPT_COMMAND
                  If set, the value is executed as a command prior to issuing each
                  primary prompt.
           PROMPT_DIRTRIM
                  If set to a number greater than zero, the value is used  as  the
                  number of trailing directory components to retain when expanding
                  the \w and \W  prompt  string  escapes  (see  PROMPTING  below).
                  Characters removed are replaced with an ellipsis.
           PS1    The  value  of  this parameter is expanded (see PROMPTING below)
                  and used as the primary prompt string.   The  default  value  is
                  ''\s-\v\$ ''.
           PS2    The  value of this parameter is expanded as with PS1 and used as
                  the secondary prompt string.  The default is ''> ''.
           PS3    The value of this parameter is used as the prompt for the select
                  command (see SHELL GRAMMAR above).
           PS4    The  value  of  this  parameter  is expanded as with PS1 and the
                  value is printed before each command  bash  displays  during  an
                  execution  trace.  The first character of PS4 is replicated mul-
                  tiple times, as necessary, to indicate multiple levels of  indi-
                  rection.  The default is ''+ ''.
           SHELL  The full pathname to the shell is kept in this environment vari-
                  able.  If it is not set when the shell starts, bash  assigns  to
                  it the full pathname of the current user's login shell.
           TIMEFORMAT
                  The  value of this parameter is used as a format string specify-
                  ing how the timing information for pipelines prefixed  with  the
                  time  reserved word should be displayed.  The % character intro-
                  duces an escape sequence that is expanded to  a  time  value  or
                  other  information.  The escape sequences and their meanings are
                  as follows; the braces denote optional portions.
                  %%        A literal %.
                  %[p][l]R  The elapsed time in seconds.
                  %[p][l]U  The number of CPU seconds spent in user mode.
                  %[p][l]S  The number of CPU seconds spent in system mode.
                  %P        The CPU percentage, computed as (%U + %S) / %R.
    
                  The optional p is a digit specifying the precision,  the  number
                  of fractional digits after a decimal point.  A value of 0 causes
                  no decimal point or fraction to be output.  At most three places
                  after  the  decimal  point may be specified; values of p greater
                  than 3 are changed to 3.  If p is not specified, the value 3  is
                  used.
    
                  The  optional l specifies a longer format, including minutes, of
                  the form MMmSS.FFs.  The value of p determines  whether  or  not
                  the fraction is included.
    
                  If  this  variable  is not set, bash acts as if it had the value
                  $'\nreal\t%3lR\nuser\t%3lU\nsys%3lS'.  If the value is null,  no
                  timing  information  is  displayed.  A trailing newline is added
                  when the format string is displayed.
                  job control.  If this variable is set, single word  simple  com-
                  mands without redirections are treated as candidates for resump-
                  tion of an existing stopped job.  There is no ambiguity allowed;
                  if  there  is more than one job beginning with the string typed,
                  the job most recently accessed  is  selected.   The  name  of  a
                  stopped  job, in this context, is the command line used to start
                  it.  If set to the value exact, the string supplied  must  match
                  the  name  of  a  stopped  job exactly; if set to substring, the
                  string supplied needs to match a substring  of  the  name  of  a
                  stopped  job.  The substring value provides functionality analo-
                  gous to the %?  job identifier (see JOB CONTROL below).  If  set
                  to  any  other  value, the supplied string must be a prefix of a
                  stopped job's name; this provides functionality analogous to the
                  %string job identifier.
    
           histchars
                  The  two or three characters which control history expansion and
                  tokenization (see HISTORY EXPANSION below).  The first character
                  is  the history expansion character, the character which signals
                  the start of a history  expansion,  normally  '!'.   The  second
                  character  is the quick substitution character, which is used as
                  shorthand for re-running the previous command  entered,  substi-
                  tuting  one  string  for another in the command.  The default is
                  '^'.  The optional third character is the character which  indi-
                  cates  that the remainder of the line is a comment when found as
                  the first character of a word, normally '#'.  The  history  com-
                  ment character causes history substitution to be skipped for the
                  remaining words on the line.  It does not necessarily cause  the
                  shell parser to treat the rest of the line as a comment.
    
       Arrays
           Bash  provides one-dimensional indexed and associative array variables.
           Any variable may be used as an indexed array; the declare builtin  will
           explicitly  declare an array.  There is no maximum limit on the size of
           an array, nor any requirement that members be indexed or assigned  con-
           tiguously.   Indexed  arrays  are  referenced using integers (including
           arithmetic expressions)  and are  zero-based;  associative  arrays  are
           referenced using arbitrary strings.
    
           An  indexed  array is created automatically if any variable is assigned
           to using the syntax name[subscript]=value.  The subscript is treated as
           an arithmetic expression that must evaluate to a number greater than or
           equal to zero.  To explicitly declare an indexed array, use declare  -a
           name (see SHELL BUILTIN COMMANDS below).  declare -a name[subscript] is
           also accepted; the subscript is ignored.
    
           Associative arrays are created using declare -A name.
    
           Attributes may be specified for an array variable using the declare and
           readonly  builtins.  Each attribute applies to all members of an array.
    
           Arrays  are  assigned  to  using  compound  assignments  of  the   form
           The braces are required to avoid conflicts with pathname expansion.  If
           subscript is @ or *, the word expands to all members  of  name.   These
           subscripts  differ only when the word appears within double quotes.  If
           the word is double-quoted, ${name[*]} expands to a single word with the
           value  of each array member separated by the first character of the IFS
           special variable, and ${name[@]} expands each element of name to a sep-
           arate  word.   When  there  are no array members, ${name[@]} expands to
           nothing.  If the double-quoted expansion  occurs  within  a  word,  the
           expansion  of  the first parameter is joined with the beginning part of
           the original word, and the expansion of the last  parameter  is  joined
           with  the  last  part  of  the original word.  This is analogous to the
           expansion of the special parameters * and  @  (see  Special  Parameters
           above).   ${#name[subscript]}  expands  to  the  length  of ${name[sub-
           script]}.  If subscript is * or @, the expansion is the number of  ele-
           ments  in the array.  Referencing an array variable without a subscript
           is equivalent to referencing the array with a subscript of 0.
    
           An array variable is considered set if a subscript has been assigned  a
           value.  The null string is a valid value.
    
           The  unset  builtin  is  used to destroy arrays.  unset name[subscript]
           destroys the array element at index subscript.  Care must be  taken  to
           avoid  unwanted side effects caused by pathname expansion.  unset name,
           where name is an array, or unset name[subscript], where subscript is  *
           or @, removes the entire array.
    
           The  declare,  local,  and readonly builtins each accept a -a option to
           specify an indexed array and a -A  option  to  specify  an  associative
           array.   The read builtin accepts a -a option to assign a list of words
           read from the standard input to an array.  The set and declare builtins
           display  array values in a way that allows them to be reused as assign-
           ments.
    
    
    

    EXPANSION

           Expansion is performed on the command line after it has been split into
           words.   There are seven kinds of expansion performed: brace expansion,
           tilde expansion, parameter and variable  expansion,  command  substitu-
           tion, arithmetic expansion, word splitting, and pathname expansion.
    
           The  order  of expansions is: brace expansion, tilde expansion, parame-
           ter, variable and arithmetic expansion and command  substitution  (done
           in a left-to-right fashion), word splitting, and pathname expansion.
    
           On systems that can support it, there is an additional expansion avail-
           able: process substitution.
    
           Only brace expansion, word splitting, and pathname expansion can change
           the  number of words of the expansion; other expansions expand a single
           word to a single word.  The only exceptions to this are the  expansions
           of "$@" and "${name[@]}" as explained above (see PARAMETERS).
    
       Brace Expansion
           either  integers or single characters, and incr, an optional increment,
           is an integer.  When integers are supplied, the expression  expands  to
           each  number between x and y, inclusive.  Supplied integers may be pre-
           fixed with 0 to force each term to have the same width.  When either  x
           or  y  begins  with  a  zero, the shell attempts to force all generated
           terms to contain the same number of digits, zero-padding  where  neces-
           sary.   When  characters  are  supplied, the expression expands to each
           character lexicographically between x and y, inclusive.  Note that both
           x  and  y must be of the same type.  When the increment is supplied, it
           is used as the difference between each term.  The default increment  is
           1 or -1 as appropriate.
    
           Brace expansion is performed before any other expansions, and any char-
           acters special to other expansions are preserved in the result.  It  is
           strictly  textual.  Bash does not apply any syntactic interpretation to
           the context of the expansion or the text between the braces.
    
           A correctly-formed brace expansion must contain  unquoted  opening  and
           closing  braces,  and  at  least one unquoted comma or a valid sequence
           expression.  Any incorrectly formed brace expansion is left  unchanged.
           A { or , may be quoted with a backslash to prevent its being considered
           part of a brace expression.  To avoid conflicts with  parameter  expan-
           sion, the string ${ is not considered eligible for brace expansion.
    
           This construct is typically used as shorthand when the common prefix of
           the strings to be generated is longer than in the above example:
    
                  mkdir /usr/local/src/bash/{old,new,dist,bugs}
           or
                  chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
    
           Brace expansion introduces a  slight  incompatibility  with  historical
           versions  of sh.  sh does not treat opening or closing braces specially
           when they appear as part of a word, and preserves them in  the  output.
           Bash  removes  braces  from  words as a consequence of brace expansion.
           For example, a word entered to sh as file{1,2} appears  identically  in
           the  output.  The same word is output as file1 file2 after expansion by
           bash.  If strict compatibility with sh is desired, start bash with  the
           +B option or disable brace expansion with the +B option to the set com-
           mand (see SHELL BUILTIN COMMANDS below).
    
       Tilde Expansion
           If a word begins with an unquoted tilde character  ('~'),  all  of  the
           characters  preceding  the  first unquoted slash (or all characters, if
           there is no unquoted slash) are considered a tilde-prefix.  If none  of
           the  characters  in  the tilde-prefix are quoted, the characters in the
           tilde-prefix following the tilde are treated as a possible login  name.
           If  this  login name is the null string, the tilde is replaced with the
           value of the shell parameter HOME.  If HOME is unset, the  home  direc-
           tory  of  the  user executing the shell is substituted instead.  Other-
           wise, the tilde-prefix is replaced with the home  directory  associated
           with the specified login name.
           Each variable assignment is checked for unquoted tilde-prefixes immedi-
           ately following a : or the first =.  In these cases, tilde expansion is
           also performed.  Consequently, one may use file names  with  tildes  in
           assignments  to  PATH,  MAILPATH, and CDPATH, and the shell assigns the
           expanded value.
    
       Parameter Expansion
           The '$' character introduces parameter expansion, command substitution,
           or  arithmetic  expansion.  The parameter name or symbol to be expanded
           may be enclosed in braces, which are optional but serve to protect  the
           variable  to be expanded from characters immediately following it which
           could be interpreted as part of the name.
    
           When braces are used, the matching ending brace is the  first  '}'  not
           escaped  by  a  backslash  or within a quoted string, and not within an
           embedded  arithmetic  expansion,  command  substitution,  or  parameter
           expansion.
    
           ${parameter}
                  The  value of parameter is substituted.  The braces are required
                  when parameter is a positional  parameter  with  more  than  one
                  digit, or when parameter is followed by a character which is not
                  to be interpreted as part of its name.
    
           If the first character of parameter is  an  exclamation  point  (!),  a
           level  of  variable  indirection is introduced.  Bash uses the value of
           the variable formed from the rest of parameter as the name of the vari-
           able; this variable is then expanded and that value is used in the rest
           of the substitution, rather than the value of parameter  itself.   This
           is  known as indirect expansion.  The exceptions to this are the expan-
           sions of ${!prefix*} and ${!name[@]} described below.  The  exclamation
           point  must  immediately  follow  the  left brace in order to introduce
           indirection.
    
           In each of the cases below, word is subject to tilde expansion, parame-
           ter expansion, command substitution, and arithmetic expansion.
    
           When  not  performing  substring  expansion, using the forms documented
           below, bash tests for a parameter that is unset or null.  Omitting  the
           colon results in a test only for a parameter that is unset.
    
           ${parameter:-word}
                  Use  Default  Values.  If parameter is unset or null, the expan-
                  sion of word is substituted.  Otherwise, the value of  parameter
                  is substituted.
           ${parameter:=word}
                  Assign  Default  Values.   If  parameter  is  unset or null, the
                  expansion of word is assigned to parameter.  The value of param-
                  eter  is  then  substituted.   Positional parameters and special
                  parameters may not be assigned to in this way.
           ${parameter:?word}
                  Display Error if Null or Unset.  If parameter is null or  unset,
                  length must evaluate to a number greater than or equal to  zero.
                  If  offset  evaluates  to  a number less than zero, the value is
                  used as an offset from the end of the value  of  parameter.   If
                  parameter  is  @,  the  result  is  length positional parameters
                  beginning at offset.  If parameter is an indexed array name sub-
                  scripted  by  @  or  *,  the result is the length members of the
                  array beginning with ${parameter[offset]}.  A negative offset is
                  taken  relative  to  one  greater  than the maximum index of the
                  specified array.  Substring expansion applied to an  associative
                  array  produces  undefined results.  Note that a negative offset
                  must be separated from the colon by at least one space to  avoid
                  being  confused  with  the  :- expansion.  Substring indexing is
                  zero-based unless the positional parameters are used,  in  which
                  case  the  indexing starts at 1 by default.  If offset is 0, and
                  the positional parameters are used, $0 is prefixed to the  list.
    
           ${!prefix*}
           ${!prefix@}
                  Names  matching prefix.  Expands to the names of variables whose
                  names begin with prefix, separated by the first character of the
                  IFS  special variable.  When @ is used and the expansion appears
                  within double quotes, each variable name expands to  a  separate
                  word.
    
           ${!name[@]}
           ${!name[*]}
                  List  of  array  keys.  If name is an array variable, expands to
                  the list of array indices (keys) assigned in name.  If  name  is
                  not  an  array,  expands to 0 if name is set and null otherwise.
                  When @ is used and the expansion appears within  double  quotes,
                  each key expands to a separate word.
    
           ${#parameter}
                  Parameter  length.   The  length  in  characters of the value of
                  parameter is substituted.  If parameter is *  or  @,  the  value
                  substituted  is the number of positional parameters.  If parame-
                  ter is an array name subscripted by * or @,  the  value  substi-
                  tuted is the number of elements in the array.
    
           ${parameter#word}
           ${parameter##word}
                  Remove matching prefix pattern.  The word is expanded to produce
                  a pattern just as in pathname expansion.  If the pattern matches
                  the  beginning of the value of parameter, then the result of the
                  expansion is the expanded value of parameter with  the  shortest
                  matching  pattern  (the ''#'' case) or the longest matching pat-
                  tern (the ''##'' case) deleted.  If parameter is  @  or  *,  the
                  pattern  removal operation is applied to each positional parame-
                  ter in turn, and the expansion is the resultant list.  If param-
                  eter  is  an array variable subscripted with @ or *, the pattern
                  removal operation is applied to each  member  of  the  array  in
                  turn, and the expansion is the resultant list.
    
           ${parameter/pattern/string}
                  Pattern substitution.  The pattern is expanded to produce a pat-
                  tern just as in pathname expansion.  Parameter is  expanded  and
                  the  longest match of pattern against its value is replaced with
                  string.  If pattern begins with /, all matches  of  pattern  are
                  replaced   with  string.   Normally  only  the  first  match  is
                  replaced.  If pattern begins with #, it must match at the begin-
                  ning of the expanded value of parameter.  If pattern begins with
                  %, it must match at the end of the expanded value of  parameter.
                  If string is null, matches of pattern are deleted and the / fol-
                  lowing pattern may be omitted.  If parameter is @ or *, the sub-
                  stitution  operation  is applied to each positional parameter in
                  turn, and the expansion is the resultant list.  If parameter  is
                  an  array  variable  subscripted  with  @ or *, the substitution
                  operation is applied to each member of the array  in  turn,  and
                  the expansion is the resultant list.
    
           ${parameter^pattern}
           ${parameter^^pattern}
           ${parameter,pattern}
           ${parameter,,pattern}
                  Case  modification.   This expansion modifies the case of alpha-
                  betic characters in parameter.  The pattern is expanded to  pro-
                  duce  a  pattern  just as in pathname expansion.  The ^ operator
                  converts lowercase letters matching pattern to uppercase; the  ,
                  operator  converts matching uppercase letters to lowercase.  The
                  ^^ and ,, expansions  convert  each  matched  character  in  the
                  expanded  value;  the  ^ and , expansions match and convert only
                  the first character in the expanded value..  If pattern is omit-
                  ted,  it is treated like a ?, which matches every character.  If
                  parameter is @ or *, the case modification operation is  applied
                  to  each  positional parameter in turn, and the expansion is the
                  resultant list.  If parameter is an array  variable  subscripted
                  with  @ or *, the case modification operation is applied to each
                  member of the array in turn, and the expansion is the  resultant
                  list.
    
       Command Substitution
           Command substitution allows the output of a command to replace the com-
           mand name.  There are two forms:
    
                  $(command)
           or
                  `command`
    
           Bash performs the expansion by executing command and replacing the com-
           mand  substitution  with  the  standard output of the command, with any
           trailing newlines deleted.  Embedded newlines are not deleted, but they
           may  be  removed during word splitting.  The command substitution $(cat
           file) can be replaced by the equivalent but faster $(< file).
           Arithmetic expansion allows the evaluation of an arithmetic  expression
           and  the  substitution of the result.  The format for arithmetic expan-
           sion is:
    
                  $((expression))
    
           The expression is treated as if it were within  double  quotes,  but  a
           double  quote  inside  the  parentheses  is not treated specially.  All
           tokens in the expression undergo parameter expansion, string expansion,
           command  substitution, and quote removal.  Arithmetic expansions may be
           nested.
    
           The evaluation is performed according to the rules listed  below  under
           ARITHMETIC EVALUATION.  If expression is invalid, bash prints a message
           indicating failure and no substitution occurs.
    
       Process Substitution
           Process substitution is supported on systems that support  named  pipes
           (FIFOs)  or the /dev/fd method of naming open files.  It takes the form
           of <(list) or >(list).  The process list is run with its input or  out-
           put connected to a FIFO or some file in /dev/fd.  The name of this file
           is passed as an argument to the current command as the  result  of  the
           expansion.   If the >(list) form is used, writing to the file will pro-
           vide input for list.  If the <(list) form is used, the file  passed  as
           an argument should be read to obtain the output of list.
    
           When  available,  process substitution is performed simultaneously with
           parameter and variable expansion, command substitution, and  arithmetic
           expansion.
    
       Word Splitting
           The  shell  scans the results of parameter expansion, command substitu-
           tion, and arithmetic expansion that did not occur within double  quotes
           for word splitting.
    
           The  shell  treats each character of IFS as a delimiter, and splits the
           results of the other expansions into words on these characters.  If IFS
           is  unset,  or its value is exactly <space><tab><newline>, the default,
           then sequences of <space>, <tab>, and <newline> at  the  beginning  and
           end  of  the  results  of  the previous expansions are ignored, and any
           sequence of IFS characters not  at  the  beginning  or  end  serves  to
           delimit  words.   If  IFS  has  a  value  other  than the default, then
           sequences of the whitespace characters space and tab are ignored at the
           beginning  and  end of the word, as long as the whitespace character is
           in the value of IFS (an IFS whitespace character).   Any  character  in
           IFS  that is not IFS whitespace, along with any adjacent IFS whitespace
           characters, delimits a field.  A sequence of IFS whitespace  characters
           is  also  treated as a delimiter.  If the value of IFS is null, no word
           splitting occurs.
    
           Explicit null arguments ("" or '')  are  retained.   Unquoted  implicit
           null arguments, resulting from the expansion of parameters that have no
           and  the  command  is  not executed.  If the shell option nocaseglob is
           enabled, the match is performed without regard to the  case  of  alpha-
           betic  characters.   When a pattern is used for pathname expansion, the
           character ''.''  at the start of a  name  or  immediately  following  a
           slash  must  be  matched explicitly, unless the shell option dotglob is
           set.  When matching a pathname, the  slash  character  must  always  be
           matched  explicitly.   In  other  cases,  the  ''.''   character is not
           treated specially.  See the description  of  shopt  below  under  SHELL
           BUILTIN  COMMANDS  for a description of the nocaseglob, nullglob, fail-
           glob, and dotglob shell options.
    
           The GLOBIGNORE shell variable may be used to restrict the set  of  file
           names  matching  a  pattern.   If GLOBIGNORE is set, each matching file
           name that also matches one of the patterns  in  GLOBIGNORE  is  removed
           from the list of matches.  The file names ''.''  and ''..''  are always
           ignored when GLOBIGNORE is set and not null.  However, setting  GLOBIG-
           NORE  to  a non-null value has the effect of enabling the dotglob shell
           option, so all other file names beginning with a ''.''  will match.  To
           get  the  old  behavior  of ignoring file names beginning with a ''.'',
           make ''.*''  one of the patterns in GLOBIGNORE.  The dotglob option  is
           disabled when GLOBIGNORE is unset.
    
           Pattern Matching
    
           Any character that appears in a pattern, other than the special pattern
           characters described below, matches itself.  The NUL character may  not
           occur  in  a pattern.  A backslash escapes the following character; the
           escaping backslash is discarded when  matching.   The  special  pattern
           characters must be quoted if they are to be matched literally.
    
           The special pattern characters have the following meanings:
    
           *      Matches  any  string, including the null string.  When the glob-
                  star shell option is enabled, and * is used in a pathname expan-
                  sion  context,  two  adjacent  *s  used as a single pattern will
                  match all files and zero or more directories and subdirectories.
                  If  followed by a /, two adjacent *s will match only directories
                  and subdirectories.
           ?      Matches any single character.
           [...]  Matches any one of the enclosed characters.  A pair  of  charac-
                  ters separated by a hyphen denotes a range expression; any char-
                  acter that sorts between those two characters, inclusive,  using
                  the  current  locale's  collating sequence and character set, is
                  matched.  If the first character following the [ is a !  or a  ^
                  then  any  character not enclosed is matched.  The sorting order
                  of characters in range expressions is determined by the  current
                  locale  and  the value of the LC_COLLATE shell variable, if set.
                  A - may be matched by including it as the first or last  charac-
                  ter in the set.  A ] may be matched by including it as the first
                  character in the set.
    
                  Within [ and ], character classes can  be  specified  using  the
                  bol symbol.
    
           Several  extended  pattern  matching  operators are recognized.  In the
           following description, a pattern-list is a list of one or more patterns
           separated  by  a |.  Composite patterns may be formed using one or more
           of the following sub-patterns:
    
                  ?(pattern-list)
                         Matches zero or one occurrence of the given patterns
                  *(pattern-list)
                         Matches zero or more occurrences of the given patterns
                  +(pattern-list)
                         Matches one or more occurrences of the given patterns
                  @(pattern-list)
                         Matches one of the given patterns
    
           If the extglob shell option is enabled using the shopt builtin, follow-
           ing pattern matching operator is recognized as well:
    
                  !(pattern-list)
                         Matches anything except one of the given patterns
    
       Quote Removal
           After the preceding expansions, all unquoted occurrences of the charac-
           ters \, ', and " that did not result from one of the  above  expansions
           are removed.
    
    
    

    REDIRECTION

           Before  a  command  is executed, its input and output may be redirected
           using a special notation interpreted by  the  shell.   Redirection  may
           also  be  used  to open and close files for the current shell execution
           environment.  The following redirection operators may precede or appear
           anywhere within a simple command or may follow a command.  Redirections
           are processed in the order they appear, from left to right.
    
           Each redirection that may be preceded by a file descriptor  number  may
           instead be preceded by a word of the form {varname}.  In this case, for
           each redirection operator except >&- and <&-, the shell will allocate a
           file  descriptor  greater  than 10 and assign it to varname.  If >&- or
           <&- is preceded by {varname}, the value of  varname  defines  the  file
           descriptor to close.
    
           In  the  following descriptions, if the file descriptor number is omit-
           ted, and the first character of the  redirection  operator  is  <,  the
           redirection  refers  to the standard input (file descriptor 0).  If the
           first character of the  redirection  operator  is  >,  the  redirection
           refers to the standard output (file descriptor 1).
    
           The  word  following the redirection operator in the following descrip-
           tions, unless otherwise noted, is subjected to brace  expansion,  tilde
           expansion, parameter expansion, command substitution, arithmetic expan-
           sion, quote removal, pathname expansion, and  word  splitting.   If  it
           put was redirected to dirlist.
    
           Bash handles several filenames specially when they are used in redirec-
           tions, as described in the following table:
    
                  /dev/fd/fd
                         If fd is a valid integer, file descriptor  fd  is  dupli-
                         cated.
                  /dev/stdin
                         File descriptor 0 is duplicated.
                  /dev/stdout
                         File descriptor 1 is duplicated.
                  /dev/stderr
                         File descriptor 2 is duplicated.
                  /dev/tcp/host/port
                         If host is a valid hostname or Internet address, and port
                         is an integer port number or service name, bash  attempts
                         to open a TCP connection to the corresponding socket.
                  /dev/udp/host/port
                         If host is a valid hostname or Internet address, and port
                         is an integer port number or service name, bash  attempts
                         to open a UDP connection to the corresponding socket.
    
           A failure to open or create a file causes the redirection to fail.
    
           Redirections  using file descriptors greater than 9 should be used with
           care, as they may conflict with file descriptors the shell uses  inter-
           nally.
    
       Redirecting Input
           Redirection of input causes the file whose name results from the expan-
           sion of word to be opened for reading on  file  descriptor  n,  or  the
           standard input (file descriptor 0) if n is not specified.
    
           The general format for redirecting input is:
    
                  [n]<word
    
       Redirecting Output
           Redirection  of  output  causes  the  file  whose name results from the
           expansion of word to be opened for writing on file descriptor n, or the
           standard output (file descriptor 1) if n is not specified.  If the file
           does not exist it is created; if it does exist it is truncated to  zero
           size.
    
           The general format for redirecting output is:
    
                  [n]>word
    
           If  the  redirection operator is >, and the noclobber option to the set
           builtin has been enabled, the redirection will fail if the  file  whose
           name  results  from the expansion of word exists and is a regular file.
    
       Redirecting Standard Output and Standard Error
           This  construct allows both the standard output (file descriptor 1) and
           the standard error output (file descriptor 2) to be redirected  to  the
           file whose name is the expansion of word.
    
           There  are  two  formats  for  redirecting standard output and standard
           error:
    
                  &>word
           and
                  >&word
    
           Of the two forms, the first is preferred.  This is semantically equiva-
           lent to
    
                  >word 2>&1
    
       Appending Standard Output and Standard Error
           This  construct allows both the standard output (file descriptor 1) and
           the standard error output (file descriptor 2) to  be  appended  to  the
           file whose name is the expansion of word.
    
           The format for appending standard output and standard error is:
    
                  &>>word
    
           This is semantically equivalent to
    
                  >>word 2>&1
    
       Here Documents
           This  type  of  redirection  instructs the shell to read input from the
           current source until a line containing only delimiter (with no trailing
           blanks)  is seen.  All of the lines read up to that point are then used
           as the standard input for a command.
    
           The format of here-documents is:
    
                  <<[-]word
                          here-document
                  delimiter
    
           No parameter expansion, command substitution, arithmetic expansion,  or
           pathname expansion is performed on word.  If any characters in word are
           quoted, the delimiter is the result of quote removal on word,  and  the
           lines  in the here-document are not expanded.  If word is unquoted, all
           lines of the here-document are subjected to parameter  expansion,  com-
           mand  substitution,  and arithmetic expansion.  In the latter case, the
           character sequence \<newline> is ignored, and \ must be used  to  quote
           the characters \, $, and `.
           The redirection operator
    
                  [n]<&word
    
           is used to duplicate input file descriptors.  If word expands to one or
           more digits, the file descriptor denoted by n is made to be a  copy  of
           that  file  descriptor.   If  the  digits in word do not specify a file
           descriptor open for input, a redirection error occurs.  If word  evalu-
           ates  to  -,  file  descriptor n is closed.  If n is not specified, the
           standard input (file descriptor 0) is used.
    
           The operator
    
                  [n]>&word
    
           is used similarly to duplicate output file descriptors.  If  n  is  not
           specified,  the  standard  output  (file descriptor 1) is used.  If the
           digits in word do not specify a file  descriptor  open  for  output,  a
           redirection error occurs.  As a special case, if n is omitted, and word
           does not expand to one or more digits, the standard output and standard
           error are redirected as described previously.
    
       Moving File Descriptors
           The redirection operator
    
                  [n]<&digit-
    
           moves  the  file descriptor digit to file descriptor n, or the standard
           input (file descriptor 0) if n is not specified.  digit is closed after
           being duplicated to n.
    
           Similarly, the redirection operator
    
                  [n]>&digit-
    
           moves  the  file descriptor digit to file descriptor n, or the standard
           output (file descriptor 1) if n is not specified.
    
       Opening File Descriptors for Reading and Writing
           The redirection operator
    
                  [n]<>word
    
           causes the file whose name is the expansion of word to  be  opened  for
           both  reading and writing on file descriptor n, or on file descriptor 0
           if n is not specified.  If the file does not exist, it is created.
    
    
    

    ALIASES

           Aliases allow a string to be substituted for a word when it is used  as
           the  first  word  of  a  simple command.  The shell maintains a list of
           aliases that may be set and unset with the alias  and  unalias  builtin
           commands  (see  SHELL  BUILTIN COMMANDS below).  The first word of each
    
           There  is no mechanism for using arguments in the replacement text.  If
           arguments are needed, a shell function should be  used  (see  FUNCTIONS
           below).
    
           Aliases  are not expanded when the shell is not interactive, unless the
           expand_aliases shell option is set using shopt (see the description  of
           shopt under SHELL BUILTIN COMMANDS below).
    
           The  rules  concerning  the  definition and use of aliases are somewhat
           confusing.  Bash always reads at  least  one  complete  line  of  input
           before  executing  any  of  the  commands  on  that  line.  Aliases are
           expanded when a command is read, not when it is  executed.   Therefore,
           an  alias definition appearing on the same line as another command does
           not take effect until the next line of input  is  read.   The  commands
           following the alias definition on that line are not affected by the new
           alias.  This behavior is also an issue  when  functions  are  executed.
           Aliases  are  expanded when a function definition is read, not when the
           function is executed, because a function definition is  itself  a  com-
           pound command.  As a consequence, aliases defined in a function are not
           available until after that function is executed.  To  be  safe,  always
           put  alias definitions on a separate line, and do not use alias in com-
           pound commands.
    
           For almost every purpose, aliases are superseded by shell functions.
    
    
    

    FUNCTIONS

           A shell function, defined  as  described  above  under  SHELL  GRAMMAR,
           stores  a  series  of commands for later execution.  When the name of a
           shell function is used as a simple command name, the list  of  commands
           associated with that function name is executed.  Functions are executed
           in the context of the current shell;  no  new  process  is  created  to
           interpret  them  (contrast  this with the execution of a shell script).
           When a function is executed, the arguments to the function  become  the
           positional parameters during its execution.  The special parameter # is
           updated to reflect the change.  Special parameter 0 is unchanged.   The
           first  element of the FUNCNAME variable is set to the name of the func-
           tion while the function is executing.
    
           All other aspects of the  shell  execution  environment  are  identical
           between a function and its caller with these exceptions:  the DEBUG and
           RETURN traps (see the description  of  the  trap  builtin  under  SHELL
           BUILTIN  COMMANDS below) are not inherited unless the function has been
           given the trace attribute (see the description of the  declare  builtin
           below)  or  the -o functrace shell option has been enabled with the set
           builtin (in which case all  functions  inherit  the  DEBUG  and  RETURN
           traps),  and the ERR trap is not inherited unless the -o errtrace shell
           option has been enabled.
    
           Variables local to the function may be declared with the local  builtin
           command.  Ordinarily, variables and their values are shared between the
           function and its caller.
           deleted  using  the  -f  option  to the unset builtin.  Note that shell
           functions and variables with the same name may result in multiple iden-
           tically-named  entries  in  the environment passed to the shell's chil-
           dren.  Care should be taken in cases where this may cause a problem.
    
           Functions may be recursive.  No limit  is  imposed  on  the  number  of
           recursive calls.
    
    
    

    ARITHMETIC EVALUATION

           The  shell allows arithmetic expressions to be evaluated, under certain
           circumstances (see the let and declare builtin commands and  Arithmetic
           Expansion).   Evaluation  is done in fixed-width integers with no check
           for overflow, though division by 0 is trapped and flagged as an  error.
           The  operators  and their precedence, associativity, and values are the
           same as in the C language.  The following list of operators is  grouped
           into  levels  of  equal-precedence operators.  The levels are listed in
           order of decreasing precedence.
    
           id++ id--
                  variable post-increment and post-decrement
           ++id --id
                  variable pre-increment and pre-decrement
           - +    unary minus and plus
           ! ~    logical and bitwise negation
           **     exponentiation
           * / %  multiplication, division, remainder
           + -    addition, subtraction
           << >>  left and right bitwise shifts
           <= >= < >
                  comparison
           == !=  equality and inequality
           &      bitwise AND
           ^      bitwise exclusive OR
           |      bitwise OR
           &&     logical AND
           ||     logical OR
           expr?expr:expr
                  conditional operator
           = *= /= %= += -= <<= >>= &= ^= |=
                  assignment
           expr1 , expr2
                  comma
    
           Shell variables are allowed as operands; parameter  expansion  is  per-
           formed before the expression is evaluated.  Within an expression, shell
           variables may also be referenced by name without  using  the  parameter
           expansion  syntax.  A shell variable that is null or unset evaluates to
           0 when referenced by name without using the parameter expansion syntax.
           The  value  of a variable is evaluated as an arithmetic expression when
           it is referenced, or when a variable which has been given  the  integer
           attribute using declare -i is assigned a value.  A null value evaluates
           to 0.  A shell variable need not have its integer attribute  turned  on
           above.
    
    
    

    CONDITIONAL EXPRESSIONS

           Conditional  expressions  are  used  by the [[ compound command and the
           test and [ builtin commands to test file attributes and perform  string
           and  arithmetic comparisons.  Expressions are formed from the following
           unary or binary primaries.  If any file argument to  one  of  the  pri-
           maries is of the form /dev/fd/n, then file descriptor n is checked.  If
           the file argument to  one  of  the  primaries  is  one  of  /dev/stdin,
           /dev/stdout,  or /dev/stderr, file descriptor 0, 1, or 2, respectively,
           is checked.
    
           Unless otherwise specified, primaries that operate on files follow sym-
           bolic links and operate on the target of the link, rather than the link
           itself.
    
           When used with [[, The < and > operators sort  lexicographically  using
           the current locale.
    
           -a file
                  True if file exists.
           -b file
                  True if file exists and is a block special file.
           -c file
                  True if file exists and is a character special file.
           -d file
                  True if file exists and is a directory.
           -e file
                  True if file exists.
           -f file
                  True if file exists and is a regular file.
           -g file
                  True if file exists and is set-group-id.
           -h file
                  True if file exists and is a symbolic link.
           -k file
                  True if file exists and its ''sticky'' bit is set.
           -p file
                  True if file exists and is a named pipe (FIFO).
           -r file
                  True if file exists and is readable.
           -s file
                  True if file exists and has a size greater than zero.
           -t fd  True if file descriptor fd is open and refers to a terminal.
           -u file
                  True if file exists and its set-user-id bit is set.
           -w file
                  True if file exists and is writable.
           -x file
                  True if file exists and is executable.
           -O file
                  True if file exists and is owned by the effective user id.
                  does not.
           file1 -ef file2
                  True if file1 and file2 refer to the same device and inode  num-
                  bers.
           -o optname
                  True  if  shell  option  optname  is  enabled.   See the list of
                  options under the description  of  the  -o  option  to  the  set
                  builtin below.
           -z string
                  True if the length of string is zero.
           string
           -n string
                  True if the length of string is non-zero.
    
           string1 == string2
           string1 = string2
                  True  if  the strings are equal.  = should be used with the test
                  command for POSIX conformance.
    
           string1 != string2
                  True if the strings are not equal.
    
           string1 < string2
                  True if string1 sorts before string2 lexicographically.
    
           string1 > string2
                  True if string1 sorts after string2 lexicographically.
    
           arg1 OP arg2
                  OP is one of -eq, -ne, -lt, -le, -gt, or -ge.  These  arithmetic
                  binary  operators return true if arg1 is equal to, not equal to,
                  less than, less than or equal to, greater than, or greater  than
                  or  equal  to arg2, respectively.  Arg1 and arg2 may be positive
                  or negative integers.
    
    
    

    SIMPLE COMMAND EXPANSION

           When a simple command is executed, the  shell  performs  the  following
           expansions, assignments, and redirections, from left to right.
    
           1.     The  words  that  the  parser has marked as variable assignments
                  (those preceding the command name) and  redirections  are  saved
                  for later processing.
    
           2.     The  words that are not variable assignments or redirections are
                  expanded.  If any words remain after expansion, the  first  word
                  is  taken  to be the name of the command and the remaining words
                  are the arguments.
    
           3.     Redirections are performed as described above under REDIRECTION.
    
           4.     The text after the = in each variable assignment undergoes tilde
                  expansion, parameter expansion, command substitution, arithmetic
    
           If  there is a command name left after expansion, execution proceeds as
           described below.  Otherwise, the command exits.  If one of  the  expan-
           sions  contained a command substitution, the exit status of the command
           is the exit status of the  last  command  substitution  performed.   If
           there were no command substitutions, the command exits with a status of
           zero.
    
    
    

    COMMAND EXECUTION

           After a command has been split into words, if it results  in  a  simple
           command  and  an  optional list of arguments, the following actions are
           taken.
    
           If the command name contains no slashes, the shell attempts  to  locate
           it.   If  there  exists a shell function by that name, that function is
           invoked as described above in FUNCTIONS.  If the name does not match  a
           function,  the shell searches for it in the list of shell builtins.  If
           a match is found, that builtin is invoked.
    
           If the name is neither a shell function nor a builtin, and contains  no
           slashes,  bash  searches  each element of the PATH for a directory con-
           taining an executable file by that name.  Bash uses  a  hash  table  to
           remember  the  full pathnames of executable files (see hash under SHELL
           BUILTIN COMMANDS below).  A full search of the directories in  PATH  is
           performed  only  if the command is not found in the hash table.  If the
           search is unsuccessful, the shell searches for a defined shell function
           named command_not_found_handle.  If that function exists, it is invoked
           with the original command and the original command's arguments  as  its
           arguments,  and  the  function's exit status becomes the exit status of
           the shell.  If that function is not defined, the shell prints an  error
           message and returns an exit status of 127.
    
           If  the  search  is  successful, or if the command name contains one or
           more slashes, the shell executes the named program in a separate execu-
           tion environment.  Argument 0 is set to the name given, and the remain-
           ing arguments to the command are set to the arguments given, if any.
    
           If this execution fails because the file is not in  executable  format,
           and  the file is not a directory, it is assumed to be a shell script, a
           file containing shell commands.  A subshell is spawned to  execute  it.
           This  subshell  reinitializes itself, so that the effect is as if a new
           shell had been invoked to handle the script, with  the  exception  that
           the  locations  of  commands  remembered  by the parent (see hash below
           under SHELL BUILTIN COMMANDS) are retained by the child.
    
           If the program is a file beginning with #!, the remainder of the  first
           line  specifies an interpreter for the program.  The shell executes the
           specified interpreter on operating systems that do not handle this exe-
           cutable format themselves.  The arguments to the interpreter consist of
           a single optional argument following the interpreter name on the  first
           line  of  the program, followed by the name of the program, followed by
           the command arguments, if any.
    
           ?      current traps set by trap
    
           ?      shell parameters that are set by variable assignment or with set
                  or inherited from the shell's parent in the environment
    
           ?      shell  functions  defined during execution or inherited from the
                  shell's parent in the environment
    
           ?      options enabled at invocation (either by default  or  with  com-
                  mand-line arguments) or by set
    
           ?      options enabled by shopt
    
           ?      shell aliases defined with alias
    
           ?      various  process  IDs,  including  those of background jobs, the
                  value of $$, and the value of PPID
    
           When a simple command other than a builtin or shell function is  to  be
           executed,  it  is invoked in a separate execution environment that con-
           sists of the following.  Unless otherwise noted, the values are  inher-
           ited from the shell.
    
           ?      the  shell's  open  files,  plus any modifications and additions
                  specified by redirections to the command
    
           ?      the current working directory
    
           ?      the file creation mode mask
    
           ?      shell variables and functions  marked  for  export,  along  with
                  variables exported for the command, passed in the environment
    
           ?      traps caught by the shell are reset to the values inherited from
                  the shell's parent, and traps ignored by the shell are ignored
    
           A command invoked  in  this  separate  environment  cannot  affect  the
           shell's execution environment.
    
           Command  substitution,  commands  grouped  with  parentheses, and asyn-
           chronous commands are invoked in  a  subshell  environment  that  is  a
           duplicate  of  the  shell  environment, except that traps caught by the
           shell are reset to the values that the shell inherited from its  parent
           at invocation.  Builtin commands that are invoked as part of a pipeline
           are also executed in a subshell environment.  Changes made to the  sub-
           shell environment cannot affect the shell's execution environment.
    
           Subshells spawned to execute command substitutions inherit the value of
           the -e option from the parent shell.  When  not  in  posix  mode,  Bash
           clears the -e option in such subshells.
    
           declare -x commands allow parameters and functions to be added  to  and
           deleted from the environment.  If the value of a parameter in the envi-
           ronment is modified, the new value becomes  part  of  the  environment,
           replacing  the  old.  The environment inherited by any executed command
           consists of the shell's initial environment, whose values may be  modi-
           fied  in  the  shell, less any pairs removed by the unset command, plus
           any additions via the export and declare -x commands.
    
           The environment for any simple command or  function  may  be  augmented
           temporarily  by  prefixing  it with parameter assignments, as described
           above in PARAMETERS.  These assignment statements affect only the envi-
           ronment seen by that command.
    
           If  the  -k option is set (see the set builtin command below), then all
           parameter assignments are placed in the environment for a command,  not
           just those that precede the command name.
    
           When  bash  invokes  an  external command, the variable _ is set to the
           full file name of the command and passed to that command in  its  envi-
           ronment.
    
    
    

    EXIT STATUS

           The  exit  status  of  an executed command is the value returned by the
           waitpid system call or equivalent function.  Exit statuses fall between
           0  and  255, though, as explained below, the shell may use values above
           125 specially.  Exit statuses from shell builtins and compound commands
           are  also limited to this range. Under certain circumstances, the shell
           will use special values to indicate specific failure modes.
    
           For the shell's purposes, a command which exits with a zero exit status
           has  succeeded.   An exit status of zero indicates success.  A non-zero
           exit status indicates failure.  When a command terminates  on  a  fatal
           signal N, bash uses the value of 128+N as the exit status.
    
           If  a  command  is  not  found, the child process created to execute it
           returns a status of 127.  If a command is found but is not  executable,
           the return status is 126.
    
           If a command fails because of an error during expansion or redirection,
           the exit status is greater than zero.
    
           Shell builtin commands return a status of 0 (true) if  successful,  and
           non-zero  (false)  if an error occurs while they execute.  All builtins
           return an exit status of 2 to indicate incorrect usage.
    
           Bash itself returns the exit  status  of  the  last  command  executed,
           unless  a  syntax  error occurs, in which case it exits with a non-zero
           value.  See also the exit builtin command below.
    
    
    

    SIGNALS

           When bash is interactive, in the  absence  of  any  traps,  it  ignores
           SIGTERM (so that kill 0 does not kill an interactive shell), and SIGINT
           SIGHUP.  To prevent the shell from sending the signal to  a  particular
           job,  it  should be removed from the jobs table with the disown builtin
           (see SHELL BUILTIN COMMANDS below) or  marked  to  not  receive  SIGHUP
           using disown -h.
    
           If  the  huponexit  shell  option has been set with shopt, bash sends a
           SIGHUP to all jobs when an interactive login shell exits.
    
           If bash is waiting for a command to complete and receives a signal  for
           which a trap has been set, the trap will not be executed until the com-
           mand completes.  When bash is waiting for an asynchronous  command  via
           the  wait  builtin, the reception of a signal for which a trap has been
           set will cause the wait builtin to return immediately with an exit sta-
           tus greater than 128, immediately after which the trap is executed.
    
    
    

    JOB CONTROL

           Job  control  refers  to  the ability to selectively stop (suspend) the
           execution of processes and continue (resume) their execution at a later
           point.   A  user  typically  employs  this  facility via an interactive
           interface supplied jointly by the operating  system  kernel's  terminal
           driver and bash.
    
           The  shell  associates  a  job with each pipeline.  It keeps a table of
           currently executing jobs, which may be listed with  the  jobs  command.
           When  bash starts a job asynchronously (in the background), it prints a
           line that looks like:
    
                  [1] 25647
    
           indicating that this job is job number 1 and that the process ID of the
           last process in the pipeline associated with this job is 25647.  All of
           the processes in a single pipeline are members of the same  job.   Bash
           uses the job abstraction as the basis for job control.
    
           To  facilitate the implementation of the user interface to job control,
           the operating system maintains the notion of a current terminal process
           group ID.  Members of this process group (processes whose process group
           ID is equal to the current terminal process group ID) receive keyboard-
           generated  signals  such  as SIGINT.  These processes are said to be in
           the foreground.  Background processes are those whose process group  ID
           differs from the terminal's; such processes are immune to keyboard-gen-
           erated signals.  Only foreground processes are allowed to read from or,
           if  the  user  so  specifies  with  stty tostop, write to the terminal.
           Background processes which attempt to read from  (write  to  when  stty
           tostop  is  in effect) the terminal are sent a SIGTTIN (SIGTTOU) signal
           by the kernel's terminal driver, which,  unless  caught,  suspends  the
           process.
    
           If  the operating system on which bash is running supports job control,
           bash contains facilities to use it.  Typing the suspend character (typ-
           ically ^Z, Control-Z) while a process is running causes that process to
           be stopped and returns control to bash.   Typing  the  delayed  suspend
           other  hand,  refers to any job containing the string ce in its command
           line.  If the substring matches more than  one  job,  bash  reports  an
           error.   The  symbols %% and %+ refer to the shell's notion of the cur-
           rent job, which is the last job stopped while it was in the  foreground
           or started in the background.  The previous job may be referenced using
           %-.  If there is only a single job, %+ and %- can both be used to refer
           to  that  job.   In  output pertaining to jobs (e.g., the output of the
           jobs command), the current job is always flagged with a +, and the pre-
           vious  job  with  a -.  A single % (with no accompanying job specifica-
           tion) also refers to the current job.
    
           Simply naming a job can be used to bring it into the foreground: %1  is
           a  synonym  for  ''fg %1'', bringing job 1 from the background into the
           foreground.  Similarly, ''%1 &''  resumes  job  1  in  the  background,
           equivalent to ''bg %1''.
    
           The  shell  learns immediately whenever a job changes state.  Normally,
           bash waits until it is about to print a prompt before reporting changes
           in  a  job's status so as to not interrupt any other output.  If the -b
           option to the set builtin command is enabled, bash reports such changes
           immediately.   Any  trap  on  SIGCHLD  is  executed for each child that
           exits.
    
           If an attempt to exit bash is made while jobs are stopped (or,  if  the
           checkjobs  shell  option has been enabled using the shopt builtin, run-
           ning), the shell prints a warning message, and, if the checkjobs option
           is  enabled,  lists  the jobs and their statuses.  The jobs command may
           then be used to inspect their status.  If a second attempt to  exit  is
           made  without  an intervening command, the shell does not print another
           warning, and any stopped jobs are terminated.
    
    
    

    PROMPTING

           When executing interactively, bash displays the primary prompt PS1 when
           it  is  ready  to  read a command, and the secondary prompt PS2 when it
           needs more input to complete  a  command.   Bash  allows  these  prompt
           strings  to  be  customized  by inserting a number of backslash-escaped
           special characters that are decoded as follows:
                  \a     an ASCII bell character (07)
                  \d     the date in "Weekday Month Date" format (e.g.,  "Tue  May
                         26")
                  \D{format}
                         the  format  is  passed  to strftime(3) and the result is
                         inserted into the prompt string; an empty format  results
                         in a locale-specific time representation.  The braces are
                         required
                  \e     an ASCII escape character (033)
                  \h     the hostname up to the first '.'
                  \H     the hostname
                  \j     the number of jobs currently managed by the shell
                  \l     the basename of the shell's terminal device name
                  \n     newline
                  \r     carriage return
                  \!     the history number of this command
                  \#     the command number of this command
                  \$     if the effective UID is 0, a #, otherwise a $
                  \nnn   the character corresponding to the octal number nnn
                  \\     a backslash
                  \[     begin  a sequence of non-printing characters, which could
                         be used to embed a terminal  control  sequence  into  the
                         prompt
                  \]     end a sequence of non-printing characters
    
           The  command  number  and the history number are usually different: the
           history number of a command is its position in the history list,  which
           may  include  commands  restored  from  the  history  file (see HISTORY
           below), while the command number is the position  in  the  sequence  of
           commands  executed  during the current shell session.  After the string
           is decoded, it is expanded via parameter expansion,  command  substitu-
           tion,  arithmetic expansion, and quote removal, subject to the value of
           the promptvars shell option (see the description of the  shopt  command
           under SHELL BUILTIN COMMANDS below).
    
    
    

    READLINE

           This  is  the library that handles reading input when using an interac-
           tive shell, unless the --noediting option is given at shell invocation.
           Line editing is also used when using the -e option to the read builtin.
           By default, the line editing commands are similar to those of emacs.  A
           vi-style line editing interface is also available.  Line editing can be
           enabled at any time using the -o emacs or -o  vi  options  to  the  set
           builtin  (see  SHELL BUILTIN COMMANDS below).  To turn off line editing
           after the shell is running, use the +o emacs or +o vi  options  to  the
           set builtin.
    
       Readline Notation
           In this section, the emacs-style notation is used to denote keystrokes.
           Control keys are denoted by C-key, e.g., C-n  means  Control-N.   Simi-
           larly,  meta  keys are denoted by M-key, so M-x means Meta-X.  (On key-
           boards without a meta key, M-x means ESC x, i.e., press the Escape  key
           then the x key.  This makes ESC the meta prefix.  The combination M-C-x
           means ESC-Control-x, or press the Escape key then hold the Control  key
           while pressing the x key.)
    
           Readline commands may be given numeric arguments, which normally act as
           a repeat count.  Sometimes, however, it is the  sign  of  the  argument
           that  is  significant.   Passing  a negative argument to a command that
           acts in the forward direction (e.g., kill-line) causes that command  to
           act  in  a  backward direction.  Commands whose behavior with arguments
           deviates from this are noted below.
    
           When a command is described as killing text, the text deleted is  saved
           for possible future retrieval (yanking).  The killed text is saved in a
           kill ring.  Consecutive kills cause the text to be accumulated into one
           unit, which can be yanked all at once.  Commands which do not kill text
           separate the chunks of text on the kill ring.
    
           For example, placing
    
                  M-Control-u: universal-argument
           or
                  C-Meta-u: universal-argument
           into the inputrc would make M-C-u execute the readline command  univer-
           sal-argument.
    
           The  following  symbolic  character  names are recognized: RUBOUT, DEL,
           ESC, LFD, NEWLINE, RET, RETURN, SPC, SPACE, and TAB.
    
           In addition to command names, readline allows keys to  be  bound  to  a
           string that is inserted when the key is pressed (a macro).
    
       Readline Key Bindings
           The  syntax for controlling key bindings in the inputrc file is simple.
           All that is required is the name of the command or the text of a  macro
           and  a key sequence to which it should be bound. The name may be speci-
           fied in one of two ways: as a symbolic key name, possibly with Meta- or
           Control- prefixes, or as a key sequence.
    
           When using the form keyname:function-name or macro, keyname is the name
           of a key spelled out in English.  For example:
    
                  Control-u: universal-argument
                  Meta-Rubout: backward-kill-word
                  Control-o: "> output"
    
           In the above example, C-u is bound to the function  universal-argument,
           M-DEL  is bound to the function backward-kill-word, and C-o is bound to
           run the macro expressed on the right hand side (that is, to insert  the
           text ''> output'' into the line).
    
           In  the  second  form,  "keyseq":function-name or macro, keyseq differs
           from keyname above in that strings denoting an entire key sequence  may
           be  specified  by  placing the sequence within double quotes.  Some GNU
           Emacs style key escapes can be used, as in the following  example,  but
           the symbolic character names are not recognized.
    
                  "\C-u": universal-argument
                  "\C-x\C-r": re-read-init-file
                  "\e[11~": "Function Key 1"
    
           In this example, C-u is again bound to the function universal-argument.
           C-x C-r is bound to the function re-read-init-file, and ESC [ 1 1 ~  is
           bound to insert the text ''Function Key 1''.
    
           The full set of GNU Emacs style escape sequences is
                  \C-    control prefix
                  \M-    meta prefix
                  \e     an escape character
                  \nnn   the eight-bit character whose value is  the  octal  value
                         nnn (one to three digits)
                  \xHH   the  eight-bit  character  whose value is the hexadecimal
                         value HH (one or two hex digits)
    
           When entering the text of a macro, single or double quotes must be used
           to indicate a macro definition.  Unquoted text is assumed to be a func-
           tion name.  In the macro body, the backslash  escapes  described  above
           are  expanded.   Backslash  will quote any other character in the macro
           text, including " and '.
    
           Bash allows the current readline key bindings to be displayed or  modi-
           fied  with  the bind builtin command.  The editing mode may be switched
           during interactive use by using the -o option to the set  builtin  com-
           mand (see SHELL BUILTIN COMMANDS below).
    
       Readline Variables
           Readline has variables that can be used to further customize its behav-
           ior.  A variable may be set in the inputrc file with a statement of the
           form
    
                  set variable-name value
    
           Except  where  noted,  readline variables can take the values On or Off
           (without regard to case).  Unrecognized  variable  names  are  ignored.
           When  a variable value is read, empty or null values, "on" (case-insen-
           sitive), and "1" are equivalent to On.  All other values are equivalent
           to Off.  The variables and their default values are:
    
           bell-style (audible)
                  Controls  what  happens when readline wants to ring the terminal
                  bell.  If set to none, readline never rings the bell.  If set to
                  visible,  readline  uses a visible bell if one is available.  If
                  set to audible, readline attempts to ring the terminal's bell.
           bind-tty-special-chars (On)
                  If set to On, readline attempts to bind the  control  characters
                  treated specially by the kernel's terminal driver to their read-
                  line equivalents.
           comment-begin (''#'')
                  The string that is inserted  when  the  readline  insert-comment
                  command is executed.  This command is bound to M-# in emacs mode
                  and to # in vi command mode.
           completion-ignore-case (Off)
                  If set to On, readline performs filename matching and completion
                  in a case-insensitive fashion.
           completion-prefix-display-length (0)
                  The  length in characters of the common prefix of a list of pos-
                  sible completions that is displayed without modification.   When
                  set  to  a  value greater than zero, common prefixes longer than
                  this value are replaced with an ellipsis when displaying  possi-
                  ble completions.
           completion-query-items (100)
                  characters  will  be  inserted into the line as if they had been
                  mapped to self-insert.
           editing-mode (emacs)
                  Controls whether readline begins with a set of key bindings sim-
                  ilar to emacs or vi.  editing-mode can be set to either emacs or
                  vi.
           echo-control-characters (On)
                  When set to On, on operating systems that indicate they  support
                  it, readline echoes a character corresponding to a signal gener-
                  ated from the keyboard.
           enable-keypad (Off)
                  When set to On, readline will try to enable the application key-
                  pad  when  it  is  called.  Some systems need this to enable the
                  arrow keys.
           enable-meta-key (On)
                  When set to On, readline will try to enable  any  meta  modifier
                  key  the  terminal claims to support when it is called.  On many
                  terminals, the meta key is used to send eight-bit characters.
           expand-tilde (Off)
                  If set  to  on,  tilde  expansion  is  performed  when  readline
                  attempts word completion.
           history-preserve-point (Off)
                  If  set  to  on, the history code attempts to place point at the
                  same location on each history line retrieved with  previous-his-
                  tory or next-history.
           history-size (0)
                  Set  the  maximum number of history entries saved in the history
                  list.  If set to zero, the number of entries in the history list
                  is not limited.
           horizontal-scroll-mode (Off)
                  When  set  to  On, makes readline use a single line for display,
                  scrolling the input horizontally on a single screen line when it
                  becomes  longer  than the screen width rather than wrapping to a
                  new line.
           input-meta (Off)
                  If set to On, readline will enable eight-bit input (that is,  it
                  will  not  strip  the  high  bit  from the characters it reads),
                  regardless of what the terminal claims it can support.  The name
                  meta-flag is a synonym for this variable.
           isearch-terminators (''C-[C-J'')
                  The  string  of  characters that should terminate an incremental
                  search without subsequently executing the character  as  a  com-
                  mand.   If this variable has not been given a value, the charac-
                  ters ESC and C-J will terminate an incremental search.
           keymap (emacs)
                  Set the current readline keymap.  The set of valid keymap  names
                  is  emacs,  emacs-standard,  emacs-meta, emacs-ctlx, vi, vi-com-
                  mand, and vi-insert.  vi is equivalent to vi-command;  emacs  is
                  equivalent  to  emacs-standard.  The default value is emacs; the
                  value of editing-mode also affects the default keymap.
           mark-directories (On)
                  If set to On, completed directory names have a slash appended.
                  bit set directly rather than as a meta-prefixed escape sequence.
           page-completions (On)
                  If set to On, readline uses an internal more-like pager to  dis-
                  play a screenful of possible completions at a time.
           print-completions-horizontally (Off)
                  If  set  to  On,  readline will display completions with matches
                  sorted horizontally in alphabetical order, rather than down  the
                  screen.
           revert-all-at-newline (Off)
                  If  set  to  on, readline will undo all changes to history lines
                  before returning when accept-line is executed.  By default, his-
                  tory  lines  may  be  modified  and retain individual undo lists
                  across calls to readline.
           show-all-if-ambiguous (Off)
                  This alters the default behavior of  the  completion  functions.
                  If set to on, words which have more than one possible completion
                  cause the matches to be listed immediately  instead  of  ringing
                  the bell.
           show-all-if-unmodified (Off)
                  This  alters the default behavior of the completion functions in
                  a fashion similar to show-all-if-ambiguous.  If set to on, words
                  which  have more than one possible completion without any possi-
                  ble partial completion (the possible completions don't  share  a
                  common  prefix)  cause  the  matches  to  be  listed immediately
                  instead of ringing the bell.
           skip-completed-text (Off)
                  If set to On, this alters the default completion  behavior  when
                  inserting  a  single match into the line.  It's only active when
                  performing completion in the middle  of  a  word.   If  enabled,
                  readline  does  not  insert  characters from the completion that
                  match characters after point in the  word  being  completed,  so
                  portions of the word following the cursor are not duplicated.
           visible-stats (Off)
                  If  set to On, a character denoting a file's type as reported by
                  stat(2) is appended to the filename when listing  possible  com-
                  pletions.
    
       Readline Conditional Constructs
           Readline  implements  a  facility  similar in spirit to the conditional
           compilation features of the C preprocessor which  allows  key  bindings
           and  variable  settings  to be performed as the result of tests.  There
           are four parser directives used.
    
           $if    The $if construct allows bindings to be made based on the  edit-
                  ing  mode,  the  terminal  being  used, or the application using
                  readline.  The text of the test extends to the end of the  line;
                  no characters are required to isolate it.
    
                  mode   The  mode=  form  of  the  $if  directive is used to test
                         whether readline is in emacs or vi  mode.   This  may  be
                         used  in  conjunction  with  the  set keymap command, for
                         instance, to  set  bindings  in  the  emacs-standard  and
                         library sets the application name, and an  initialization
                         file can test for a particular value.  This could be used
                         to bind key sequences to functions useful for a  specific
                         program.   For instance, the following command adds a key
                         sequence that quotes the  current  or  previous  word  in
                         Bash:
    
                         $if Bash
                         # Quote the current or previous word
                         "\C-xq": "\eb\"\ef\""
                         $endif
    
           $endif This command, as seen in the previous example, terminates an $if
                  command.
    
           $else  Commands in this branch of the $if directive are executed if the
                  test fails.
    
           $include
                  This  directive takes a single filename as an argument and reads
                  commands  and  bindings  from  that  file.   For  example,   the
                  following directive would read /etc/inputrc:
    
                  $include  /etc/inputrc
    
       Searching
           Readline  provides  commands  for searching through the command history
           (see HISTORY below) for lines containing a specified string.  There are
           two search modes: incremental and non-incremental.
    
           Incremental  searches  begin  before  the  user has finished typing the
           search string.  As each character of the search string is typed,  read-
           line displays the next entry from the history matching the string typed
           so far.  An incremental search requires  only  as  many  characters  as
           needed  to  find  the desired history entry.  The characters present in
           the value of the isearch-terminators variable are used to terminate  an
           incremental search.  If that variable has not been assigned a value the
           Escape and Control-J characters will terminate an  incremental  search.
           Control-G  will  abort  an  incremental search and restore the original
           line.  When the search is terminated, the history entry containing  the
           search string becomes the current line.
    
           To  find  other matching entries in the history list, type Control-S or
           Control-R as appropriate.  This will search backward or forward in  the
           history  for  the  next  entry matching the search string typed so far.
           Any other key sequence bound to a readline command will  terminate  the
           search  and  execute that command.  For instance, a newline will termi-
           nate the search and accept the line, thereby executing the command from
           the history list.
    
           Readline remembers the last incremental search string.  If two Control-
           Rs are typed without any intervening characters defining a  new  search
    
       Commands for Moving
           beginning-of-line (C-a)
                  Move to the start of the current line.
           end-of-line (C-e)
                  Move to the end of the line.
           forward-char (C-f)
                  Move forward a character.
           backward-char (C-b)
                  Move back a character.
           forward-word (M-f)
                  Move forward to the end of the next word.  Words are composed of
                  alphanumeric characters (letters and digits).
           backward-word (M-b)
                  Move  back  to the start of the current or previous word.  Words
                  are composed of alphanumeric characters (letters and digits).
           shell-forward-word
                  Move forward to the end of the next word.  Words  are  delimited
                  by non-quoted shell metacharacters.
           shell-backward-word
                  Move  back  to the start of the current or previous word.  Words
                  are delimited by non-quoted shell metacharacters.
           clear-screen (C-l)
                  Clear the screen leaving the current line  at  the  top  of  the
                  screen.   With  an  argument,  refresh  the current line without
                  clearing the screen.
           redraw-current-line
                  Refresh the current line.
    
       Commands for Manipulating the History
           accept-line (Newline, Return)
                  Accept the line regardless of where the cursor is.  If this line
                  is  non-empty, add it to the history list according to the state
                  of the HISTCONTROL variable.  If the line is a modified  history
                  line, then restore the history line to its original state.
           previous-history (C-p)
                  Fetch the previous command from the history list, moving back in
                  the list.
           next-history (C-n)
                  Fetch the next command from the history list, moving forward  in
                  the list.
           beginning-of-history (M-<)
                  Move to the first line in the history.
           end-of-history (M->)
                  Move  to  the end of the input history, i.e., the line currently
                  being entered.
           reverse-search-history (C-r)
                  Search backward starting at the current  line  and  moving  'up'
                  through  the  history  as  necessary.   This  is  an incremental
                  search.
           forward-search-history (C-s)
                  Search forward starting at the current line  and  moving  'down'
                  through  the  history  as  necessary.   This  is  an incremental
                  between the start of the current line and the point.  This is  a
                  non-incremental search.
           yank-nth-arg (M-C-y)
                  Insert  the  first argument to the previous command (usually the
                  second word on the previous line) at point.  With an argument n,
                  insert  the nth word from the previous command (the words in the
                  previous command  begin  with  word  0).   A  negative  argument
                  inserts the nth word from the end of the previous command.  Once
                  the argument n is computed, the argument is extracted as if  the
                  "!n" history expansion had been specified.
           yank-last-arg (M-., M-_)
                  Insert  the last argument to the previous command (the last word
                  of the  previous  history  entry).   With  an  argument,  behave
                  exactly  like  yank-nth-arg.   Successive calls to yank-last-arg
                  move back through the history list, inserting the last  argument
                  of each line in turn.  The history expansion facilities are used
                  to extract the last argument, as if the "!$"  history  expansion
                  had been specified.
           shell-expand-line (M-C-e)
                  Expand the line as the shell does.  This performs alias and his-
                  tory expansion as well as all of the shell word expansions.  See
                  HISTORY  EXPANSION below for a description of history expansion.
           history-expand-line (M-^)
                  Perform history expansion on  the  current  line.   See  HISTORY
                  EXPANSION below for a description of history expansion.
           magic-space
                  Perform  history  expansion  on  the  current  line and insert a
                  space.  See HISTORY EXPANSION below for a description of history
                  expansion.
           alias-expand-line
                  Perform  alias expansion on the current line.  See ALIASES above
                  for a description of alias expansion.
           history-and-alias-expand-line
                  Perform history and alias expansion on the current line.
           insert-last-argument (M-., M-_)
                  A synonym for yank-last-arg.
           operate-and-get-next (C-o)
                  Accept the current line for execution and fetch  the  next  line
                  relative  to the current line from the history for editing.  Any
                  argument is ignored.
           edit-and-execute-command (C-xC-e)
                  Invoke an editor on the current command line,  and  execute  the
                  result  as  shell  commands.   Bash  attempts to invoke $VISUAL,
                  $EDITOR, and emacs as the editor, in that order.
    
       Commands for Changing Text
           delete-char (C-d)
                  Delete the character at point.  If point is at the beginning  of
                  the  line,  there  are  no  characters in the line, and the last
                  character typed was not bound to delete-char, then return EOF.
           backward-delete-char (Rubout)
                  Delete the character behind the cursor.  When  given  a  numeric
                  point,  moving point forward as well.  If point is at the end of
                  the line, then this transposes the two characters before  point.
                  Negative arguments have no effect.
           transpose-words (M-t)
                  Drag  the  word  before  point past the word after point, moving
                  point over that word as well.  If point is at  the  end  of  the
                  line, this transposes the last two words on the line.
           upcase-word (M-u)
                  Uppercase  the  current  (or  following)  word.  With a negative
                  argument, uppercase the previous word, but do not move point.
           downcase-word (M-l)
                  Lowercase the current (or  following)  word.   With  a  negative
                  argument, lowercase the previous word, but do not move point.
           capitalize-word (M-c)
                  Capitalize  the  current  (or  following) word.  With a negative
                  argument, capitalize the previous word, but do not move point.
           overwrite-mode
                  Toggle overwrite mode.  With an explicit positive numeric  argu-
                  ment, switches to overwrite mode.  With an explicit non-positive
                  numeric argument, switches to insert mode.  This command affects
                  only  emacs mode; vi mode does overwrite differently.  Each call
                  to readline() starts in insert mode.  In overwrite mode, charac-
                  ters  bound to self-insert replace the text at point rather than
                  pushing the text  to  the  right.   Characters  bound  to  back-
                  ward-delete-char  replace  the  character  before  point  with a
                  space.  By default, this command is unbound.
    
       Killing and Yanking
           kill-line (C-k)
                  Kill the text from point to the end of the line.
           backward-kill-line (C-x Rubout)
                  Kill backward to the beginning of the line.
           unix-line-discard (C-u)
                  Kill backward from point to the  beginning  of  the  line.   The
                  killed text is saved on the kill-ring.
           kill-whole-line
                  Kill  all  characters on the current line, no matter where point
                  is.
           kill-word (M-d)
                  Kill from point to the end of the current word,  or  if  between
                  words,  to  the  end  of the next word.  Word boundaries are the
                  same as those used by forward-word.
           backward-kill-word (M-Rubout)
                  Kill the word behind point.  Word boundaries  are  the  same  as
                  those used by backward-word.
           shell-kill-word (M-d)
                  Kill  from  point  to the end of the current word, or if between
                  words, to the end of the next word.   Word  boundaries  are  the
                  same as those used by shell-forward-word.
           shell-backward-kill-word (M-Rubout)
                  Kill  the  word  behind  point.  Word boundaries are the same as
                  those used by shell-backward-word.
                  Copy  the word before point to the kill buffer.  The word bound-
                  aries are the same as backward-word.
           copy-forward-word
                  Copy the word following point to  the  kill  buffer.   The  word
                  boundaries are the same as forward-word.
           yank (C-y)
                  Yank the top of the kill ring into the buffer at point.
           yank-pop (M-y)
                  Rotate  the kill ring, and yank the new top.  Only works follow-
                  ing yank or yank-pop.
    
       Numeric Arguments
           digit-argument (M-0, M-1, ..., M--)
                  Add this digit to the argument already accumulating, or start  a
                  new argument.  M-- starts a negative argument.
           universal-argument
                  This  is another way to specify an argument.  If this command is
                  followed by one or more digits, optionally with a leading  minus
                  sign,  those digits define the argument.  If the command is fol-
                  lowed by digits, executing  universal-argument  again  ends  the
                  numeric  argument, but is otherwise ignored.  As a special case,
                  if this command is immediately followed by a character  that  is
                  neither  a  digit or minus sign, the argument count for the next
                  command is multiplied by four.  The argument count is  initially
                  one,  so  executing this function the first time makes the argu-
                  ment count four, a second time makes the argument count sixteen,
                  and so on.
    
       Completing
           complete (TAB)
                  Attempt  to  perform  completion on the text before point.  Bash
                  attempts completion treating the text as a variable (if the text
                  begins  with  $), username (if the text begins with ~), hostname
                  (if the text begins with @), or command (including  aliases  and
                  functions) in turn.  If none of these produces a match, filename
                  completion is attempted.
           possible-completions (M-?)
                  List the possible completions of the text before point.
           insert-completions (M-*)
                  Insert all completions of the text before point that would  have
                  been generated by possible-completions.
           menu-complete
                  Similar  to complete, but replaces the word to be completed with
                  a single match from the list of possible completions.   Repeated
                  execution  of  menu-complete  steps through the list of possible
                  completions, inserting each match in turn.  At the  end  of  the
                  list of completions, the bell is rung (subject to the setting of
                  bell-style) and the original text is restored.  An argument of n
                  moves  n  positions  forward  in the list of matches; a negative
                  argument may be used to move backward through  the  list.   This
                  command  is  intended  to  be  bound  to  TAB, but is unbound by
                  defaultc
    
           complete-username (M-~)
                  Attempt completion on the text before point, treating  it  as  a
                  username.
           possible-username-completions (C-x ~)
                  List the possible completions of the text before point, treating
                  it as a username.
           complete-variable (M-$)
                  Attempt completion on the text before point, treating  it  as  a
                  shell variable.
           possible-variable-completions (C-x $)
                  List the possible completions of the text before point, treating
                  it as a shell variable.
           complete-hostname (M-@)
                  Attempt completion on the text before point, treating  it  as  a
                  hostname.
           possible-hostname-completions (C-x @)
                  List the possible completions of the text before point, treating
                  it as a hostname.
           complete-command (M-!)
                  Attempt completion on the text before point, treating  it  as  a
                  command  name.   Command  completion  attempts to match the text
                  against  aliases,  reserved  words,   shell   functions,   shell
                  builtins, and finally executable filenames, in that order.
           possible-command-completions (C-x !)
                  List the possible completions of the text before point, treating
                  it as a command name.
           dynamic-complete-history (M-TAB)
                  Attempt completion on the text before point, comparing the  text
                  against  lines  from  the  history  list for possible completion
                  matches.
           dabbrev-expand
                  Attempt menu completion on the text before point, comparing  the
                  text against lines from the history list for possible completion
                  matches.
           complete-into-braces (M-{)
                  Perform filename completion and insert the list of possible com-
                  pletions  enclosed within braces so the list is available to the
                  shell (see Brace Expansion above).
    
       Keyboard Macros
           start-kbd-macro (C-x ()
                  Begin saving the characters  typed  into  the  current  keyboard
                  macro.
           end-kbd-macro (C-x ))
                  Stop saving the characters typed into the current keyboard macro
                  and store the definition.
           call-last-kbd-macro (C-x e)
                  Re-execute the last keyboard macro defined, by making the  char-
                  acters in the macro appear as if typed at the keyboard.
    
       Miscellaneous
           re-read-init-file (C-x C-r)
                  undo command enough times to return  the  line  to  its  initial
                  state.
           tilde-expand (M-&)
                  Perform tilde expansion on the current word.
           set-mark (C-@, M-<space>)
                  Set  the  mark to the point.  If a numeric argument is supplied,
                  the mark is set to that position.
           exchange-point-and-mark (C-x C-x)
                  Swap the point with the mark.  The current  cursor  position  is
                  set  to the saved position, and the old cursor position is saved
                  as the mark.
           character-search (C-])
                  A character is read and point is moved to the next occurrence of
                  that  character.   A negative count searches for previous occur-
                  rences.
           character-search-backward (M-C-])
                  A character is read and point is moved to  the  previous  occur-
                  rence  of  that character.  A negative count searches for subse-
                  quent occurrences.
           skip-csi-sequence ()
                  Read enough characters to consume a multi-key sequence  such  as
                  those  defined for keys like Home and End.  Such sequences begin
                  with a Control Sequence Indicator (CSI), usually ESC-[.  If this
                  sequence  is  bound  to "\[", keys producing such sequences will
                  have no effect unless explicitly bound to  a  readline  command,
                  instead  of  inserting stray characters into the editing buffer.
                  This is unbound by default, but usually bound to ESC-[.
           insert-comment (M-#)
                  Without a numeric argument,  the  value  of  the  readline  com-
                  ment-begin  variable is inserted at the beginning of the current
                  line.  If a numeric argument is supplied, this command acts as a
                  toggle:   if  the characters at the beginning of the line do not
                  match the value of comment-begin, the value is inserted,  other-
                  wise the characters in comment-begin are deleted from the begin-
                  ning of the line.  In either case, the line is accepted as if  a
                  newline  had  been  typed.   The  default value of comment-begin
                  causes this command to make the current line  a  shell  comment.
                  If  a  numeric  argument  causes  the  comment  character  to be
                  removed, the line will be executed by the shell.
           glob-complete-word (M-g)
                  The word before point is  treated  as  a  pattern  for  pathname
                  expansion,  with  an asterisk implicitly appended.  This pattern
                  is used to generate a list of matching file names  for  possible
                  completions.
           glob-expand-word (C-x *)
                  The  word  before  point  is  treated  as a pattern for pathname
                  expansion, and the list of  matching  file  names  is  inserted,
                  replacing  the  word.   If  a  numeric  argument is supplied, an
                  asterisk is appended before pathname expansion.
           glob-list-expansions (C-x g)
                  The list  of  expansions  that  would  have  been  generated  by
                  glob-expand-word  is  displayed,  and the line is redrawn.  If a
                  strings they output.  If a numeric  argument  is  supplied,  the
                  output is formatted in such a way that it can be made part of an
                  inputrc file.
           display-shell-version (C-x C-v)
                  Display version information about the current instance of  bash.
    
       Programmable Completion
           When  word  completion  is  attempted  for an argument to a command for
           which a completion specification (a compspec) has  been  defined  using
           the  complete  builtin  (see  SHELL  BUILTIN  COMMANDS below), the pro-
           grammable completion facilities are invoked.
    
           First, the command name is identified.  If  the  command  word  is  the
           empty  string (completion attempted at the beginning of an empty line),
           any compspec defined with the -E option to  complete  is  used.   If  a
           compspec  has  been  defined  for that command, the compspec is used to
           generate the list of possible completions for the word.  If the command
           word  is  a full pathname, a compspec for the full pathname is searched
           for first.  If no compspec is found for the full pathname,  an  attempt
           is  made  to find a compspec for the portion following the final slash.
           If those searches to not result in a  compspec,  any  compspec  defined
           with the -D option to complete is used as the default.
    
           Once  a  compspec  has  been  found, it is used to generate the list of
           matching words.  If a compspec is not found, the default  bash  comple-
           tion as described above under Completing is performed.
    
           First,  the  actions  specified by the compspec are used.  Only matches
           which are prefixed by the word being completed are returned.  When  the
           -f  or -d option is used for filename or directory name completion, the
           shell variable FIGNORE is used to filter the matches.
    
           Any completions specified by a pathname expansion  pattern  to  the  -G
           option are generated next.  The words generated by the pattern need not
           match the word being completed.  The GLOBIGNORE shell variable  is  not
           used to filter the matches, but the FIGNORE variable is used.
    
           Next,  the string specified as the argument to the -W option is consid-
           ered.  The string is first split using the characters in the  IFS  spe-
           cial  variable  as delimiters.  Shell quoting is honored.  Each word is
           then expanded using brace expansion,  tilde  expansion,  parameter  and
           variable  expansion, command substitution, and arithmetic expansion, as
           described above under EXPANSION.  The results are split using the rules
           described above under Word Splitting.  The results of the expansion are
           prefix-matched against the word being completed, and the matching words
           become the possible completions.
    
           After  these matches have been generated, any shell function or command
           specified with the -F and -C options is invoked.  When the  command  or
           function is invoked, the COMP_LINE, COMP_POINT, COMP_KEY, and COMP_TYPE
           variables are assigned values as described above under Shell Variables.
           If  a  shell  function  is being invoked, the COMP_WORDS and COMP_CWORD
           ronment equivalent to command substitution.  It should print a list  of
           completions,  one  per  line, to the standard output.  Backslash may be
           used to escape a newline, if necessary.
    
           After all of the possible completions are generated, any filter  speci-
           fied  with  the -X option is applied to the list.  The filter is a pat-
           tern as used for pathname expansion; a & in  the  pattern  is  replaced
           with  the text of the word being completed.  A literal & may be escaped
           with a backslash; the backslash is removed before attempting  a  match.
           Any  completion that matches the pattern will be removed from the list.
           A leading ! negates the pattern; in this case any completion not match-
           ing the pattern will be removed.
    
           Finally, any prefix and suffix specified with the -P and -S options are
           added to each member of the completion list, and the result is returned
           to the readline completion code as the list of possible completions.
    
           If  the previously-applied actions do not generate any matches, and the
           -o dirnames option was supplied  to  complete  when  the  compspec  was
           defined, directory name completion is attempted.
    
           If  the  -o  plusdirs option was supplied to complete when the compspec
           was defined, directory name completion is attempted and any matches are
           added to the results of the other actions.
    
           By  default,  if a compspec is found, whatever it generates is returned
           to the completion code as the full set of  possible  completions.   The
           default bash completions are not attempted, and the readline default of
           filename completion is disabled.  If the -o bashdefault option was sup-
           plied  to complete when the compspec was defined, the bash default com-
           pletions are attempted if the compspec generates no matches.  If the -o
           default  option was supplied to complete when the compspec was defined,
           readline's default completion will be performed if the  compspec  (and,
           if attempted, the default bash completions) generate no matches.
    
           When  a  compspec  indicates that directory name completion is desired,
           the programmable completion functions force readline to append a  slash
           to  completed names which are symbolic links to directories, subject to
           the value of the mark-directories readline variable, regardless of  the
           setting of the mark-symlinked-directories readline variable.
    
           There  is  some support for dynamically modifying completions.  This is
           most useful when used in combination with a default  completion  speci-
           fied  with  complete -D.  It's possible for shell functions executed as
           completion handlers to indicate that completion should  be  retried  by
           returning  an exit status of 124.  If a shell function returns 124, and
           changes the compspec associated with the command on which completion is
           being  attempted  (supplied  as the first argument when the function is
           executed), programmable completion restarts from the beginning, with an
           attempt to find a compspec for that command.  This allows a set of com-
           pletions to be built dynamically as  completion  is  attempted,  rather
           than being loaded all at once.
           provides access to the command history, the list of commands previously
           typed.   The  value  of  the HISTSIZE variable is used as the number of
           commands to save in a history list.  The text of the last HISTSIZE com-
           mands  (default  500)  is  saved.  The shell stores each command in the
           history list prior to parameter and variable expansion  (see  EXPANSION
           above)  but after history expansion is performed, subject to the values
           of the shell variables HISTIGNORE and HISTCONTROL.
    
           On startup, the history is initialized from the file named by the vari-
           able  HISTFILE  (default ~/.bash_history).  The file named by the value
           of HISTFILE is truncated, if necessary, to contain  no  more  than  the
           number  of lines specified by the value of HISTFILESIZE.  When the his-
           tory file is read, lines beginning with the history  comment  character
           followed  immediately  by a digit are interpreted as timestamps for the
           preceding history line.   These  timestamps  are  optionally  displayed
           depending  on the value of the HISTTIMEFORMAT variable.  When an inter-
           active shell exits, the last $HISTSIZE lines are copied from  the  his-
           tory list to $HISTFILE.  If the histappend shell option is enabled (see
           the description of shopt under SHELL BUILTIN COMMANDS below), the lines
           are  appended  to the history file, otherwise the history file is over-
           written.  If HISTFILE is unset, or if the history file  is  unwritable,
           the  history is not saved.  If the HISTTIMEFORMAT variable is set, time
           stamps are written to the history file, marked with the history comment
           character,  so  they may be preserved across shell sessions.  This uses
           the history comment character to distinguish timestamps from other his-
           tory lines.  After saving the history, the history file is truncated to
           contain no more than HISTFILESIZE lines.  If HISTFILESIZE is  not  set,
           no truncation is performed.
    
           The  builtin  command fc (see SHELL BUILTIN COMMANDS below) may be used
           to list or edit and re-execute a portion of the history list.  The his-
           tory  builtin  may  be  used  to display or modify the history list and
           manipulate the history file.  When using command-line  editing,  search
           commands  are available in each editing mode that provide access to the
           history list.
    
           The shell allows control over which commands are saved on  the  history
           list.  The HISTCONTROL and HISTIGNORE variables may be set to cause the
           shell to save only a subset of the commands entered.  The cmdhist shell
           option,  if enabled, causes the shell to attempt to save each line of a
           multi-line command in the same history entry, adding  semicolons  where
           necessary  to preserve syntactic correctness.  The lithist shell option
           causes the shell to save the command with embedded newlines instead  of
           semicolons.  See the description of the shopt builtin below under SHELL
           BUILTIN  COMMANDS  for  information  on  setting  and  unsetting  shell
           options.
    
    
    

    HISTORY EXPANSION

           The  shell  supports a history expansion feature that is similar to the
           history expansion in csh.  This section describes what syntax  features
           are  available.   This  feature  is  enabled by default for interactive
           shells, and can be disabled using the +H option to the set builtin com-
           words.   Various  modifiers  are  available  to manipulate the selected
           words.  The line is broken into words in the same fashion as when read-
           ing  input, so that several metacharacter-separated words surrounded by
           quotes are considered one word.  History expansions are  introduced  by
           the  appearance  of  the  history  expansion  character,  which is ! by
           default.  Only backslash (\) and single quotes can  quote  the  history
           expansion character.
    
           Several  characters inhibit history expansion if found immediately fol-
           lowing the history expansion character, even if it is unquoted:  space,
           tab,  newline,  carriage return, and =.  If the extglob shell option is
           enabled, ( will also inhibit expansion.
    
           Several shell options settable with the shopt builtin may  be  used  to
           tailor  the  behavior  of  history  expansion.  If the histverify shell
           option is enabled (see the description of the shopt builtin below), and
           readline  is  being  used,  history  substitutions  are not immediately
           passed to the shell parser.  Instead, the  expanded  line  is  reloaded
           into the readline editing buffer for further modification.  If readline
           is being used, and the histreedit shell option  is  enabled,  a  failed
           history  substitution will be reloaded into the readline editing buffer
           for correction.  The -p option to the history builtin  command  may  be
           used  to  see what a history expansion will do before using it.  The -s
           option to the history builtin may be used to add commands to the end of
           the  history  list  without  actually  executing them, so that they are
           available for subsequent recall.
    
           The shell allows control of the various characters used by the  history
           expansion mechanism (see the description of histchars above under Shell
           Variables).  The shell uses the history comment character to mark  his-
           tory timestamps when writing the history file.
    
       Event Designators
           An  event designator is a reference to a command line entry in the his-
           tory list.
    
           !      Start a history substitution, except when followed by  a  blank,
                  newline,  carriage return, = or ( (when the extglob shell option
                  is enabled using the shopt builtin).
           !n     Refer to command line n.
           !-n    Refer to the current command line minus n.
           !!     Refer to the previous command.  This is a synonym for '!-1'.
           !string
                  Refer to the most recent command starting with string.
           !?string[?]
                  Refer to the most recent command containing string.  The  trail-
                  ing ? may be omitted if string is followed immediately by a new-
                  line.
           ^string1^string2^
                  Quick substitution.  Repeat the last command, replacing  string1
                  with string2.  Equivalent to ''!!:s/string1/string2/'' (see Mod-
                  ifiers below).
    
           $      The last argument.
           %      The word matched by the most recent '?string?' search.
           x-y    A range of words; '-y' abbreviates '0-y'.
           *      All  of  the words but the zeroth.  This is a synonym for '1-$'.
                  It is not an error to use * if there is just  one  word  in  the
                  event; the empty string is returned in that case.
           x*     Abbreviates x-$.
           x-     Abbreviates x-$ like x*, but omits the last word.
    
           If  a  word  designator is supplied without an event specification, the
           previous command is used as the event.
    
       Modifiers
           After the optional word designator, there may appear a sequence of  one
           or more of the following modifiers, each preceded by a ':'.
    
           h      Remove a trailing file name component, leaving only the head.
           t      Remove all leading file name components, leaving the tail.
           r      Remove a trailing suffix of the form .xxx, leaving the basename.
           e      Remove all but the trailing suffix.
           p      Print the new command but do not execute it.
           q      Quote the substituted words, escaping further substitutions.
           x      Quote the substituted words as with q, but break into  words  at
                  blanks and newlines.
           s/old/new/
                  Substitute  new  for  the  first  occurrence of old in the event
                  line.  Any delimiter can be used  in  place  of  /.   The  final
                  delimiter  is  optional if it is the last character of the event
                  line.  The delimiter may be quoted in old and new with a  single
                  backslash.   If & appears in new, it is replaced by old.  A sin-
                  gle backslash will quote the &.  If old is null, it  is  set  to
                  the  last  old substituted, or, if no previous history substitu-
                  tions took place, the last string in a !?string[?]  search.
           &      Repeat the previous substitution.
           g      Cause changes to be applied over the entire event line.  This is
                  used  in  conjunction  with ':s' (e.g., ':gs/old/new/') or ':&'.
                  If used with ':s', any delimiter can be used in place of /,  and
                  the  final  delimiter is optional if it is the last character of
                  the event line.  An a may be used as a synonym for g.
           G      Apply the following 's' modifier once to each word in the  event
                  line.
    
    
    

    SHELL BUILTIN COMMANDS

           Unless otherwise noted, each builtin command documented in this section
           as accepting options preceded by - accepts -- to signify the end of the
           options.   The  :, true, false, and test builtins do not accept options
           and do not treat -- specially.  The exit, logout, break, continue, let,
           and  shift builtins accept and process arguments beginning with - with-
           out requiring --.  Other builtins that accept  arguments  but  are  not
           specified  as accepting options interpret arguments beginning with - as
           invalid options and require -- to prevent this interpretation.
           : [arguments]
                  searched.  If any arguments are supplied, they become the  posi-
                  tional  parameters  when  filename  is  executed.  Otherwise the
                  positional parameters are unchanged.  The return status  is  the
                  status  of  the  last  command exited within the script (0 if no
                  commands are executed), and false if filename is  not  found  or
                  cannot be read.
    
           alias [-p] [name[=value] ...]
                  Alias with no arguments or with the -p option prints the list of
                  aliases in the form alias name=value on standard  output.   When
                  arguments  are supplied, an alias is defined for each name whose
                  value is given.  A trailing space in  value causes the next word
                  to be checked for alias substitution when the alias is expanded.
                  For each name in the argument list for which no  value  is  sup-
                  plied,  the  name  and  value  of  the  alias is printed.  Alias
                  returns true unless a name is given for which no alias has  been
                  defined.
    
           bg [jobspec ...]
                  Resume  each  suspended  job jobspec in the background, as if it
                  had been started with &.  If jobspec is not present, the shell's
                  notion  of the current job is used.  bg jobspec returns 0 unless
                  run when job control is disabled or, when run with  job  control
                  enabled,  any  specified  jobspec  was  not found or was started
                  without job control.
    
           bind [-m keymap] [-lpsvPSV]
           bind [-m keymap] [-q function] [-u function] [-r keyseq]
           bind [-m keymap] -f filename
           bind [-m keymap] -x keyseq:shell-command
           bind [-m keymap] keyseq:function-name
           bind readline-command
                  Display current readline key and function bindings, bind  a  key
                  sequence  to  a  readline  function  or macro, or set a readline
                  variable.  Each non-option argument is a  command  as  it  would
                  appear  in  .inputrc, but each binding or command must be passed
                  as a separate argument; e.g.,  '"\C-x\C-r":  re-read-init-file'.
                  Options, if supplied, have the following meanings:
                  -m keymap
                         Use keymap as the keymap to be affected by the subsequent
                         bindings.  Acceptable keymap names are emacs, emacs-stan-
                         dard,  emacs-meta,  emacs-ctlx,  vi, vi-move, vi-command,
                         and vi-insert.  vi is equivalent to vi-command; emacs  is
                         equivalent to emacs-standard.
                  -l     List the names of all readline functions.
                  -p     Display  readline  function  names and bindings in such a
                         way that they can be re-read.
                  -P     List current readline function names and bindings.
                  -s     Display readline key sequences bound to  macros  and  the
                         strings  they  output  in such a way that they can be re-
                         read.
                  -S     Display readline key sequences bound to  macros  and  the
                         entered.   When shell-command is executed, the shell sets
                         the READLINE_LINE variable to the contents of  the  read-
                         line  line  buffer and the READLINE_POINT variable to the
                         current location of the insertion point.  If the executed
                         command  changes  the  value  of  READLINE_LINE  or READ-
                         LINE_POINT, those new values will  be  reflected  in  the
                         editing state.
    
                  The  return value is 0 unless an unrecognized option is given or
                  an error occurred.
    
           break [n]
                  Exit from within a for, while, until, or select loop.  If  n  is
                  specified, break n levels.  n must be >= 1.  If n is greater than
                  the number of enclosing loops, all enclosing loops  are  exited.
                  The  return  value  is  non-zero when n is <= 0; Otherwise, break
                  returns 0 value.
    
           builtin shell-builtin [arguments]
                  Execute the specified shell builtin, passing it  arguments,  and
                  return its exit status.  This is useful when defining a function
                  whose name is the same as a shell builtin, retaining  the  func-
                  tionality of the builtin within the function.  The cd builtin is
                  commonly redefined this way.  The  return  status  is  false  if
                  shell-builtin is not a shell builtin command.
    
           caller [expr]
                  Returns the context of any active subroutine call (a shell func-
                  tion or a script executed with the . or source builtins.   With-
                  out expr, caller displays the line number and source filename of
                  the current subroutine call.  If a non-negative integer is  sup-
                  plied as expr, caller displays the line number, subroutine name,
                  and source file corresponding to that position  in  the  current
                  execution  call  stack.  This extra information may be used, for
                  example, to print a stack trace.  The current frame is frame  0.
                  The  return  value is 0 unless the shell is not executing a sub-
                  routine call or expr does not correspond to a valid position  in
                  the call stack.
    
           cd [-L|-P] [dir]
                  Change  the  current directory to dir.  The variable HOME is the
                  default dir.  The variable CDPATH defines the  search  path  for
                  the  directory  containing  dir.  Alternative directory names in
                  CDPATH are separated by a colon (:).  A null directory  name  in
                  CDPATH  is  the  same as the current directory, i.e., ''.''.  If
                  dir begins with a slash (/), then CDPATH is  not  used.  The  -P
                  option  says  to use the physical directory structure instead of
                  following symbolic links (see also the  -P  option  to  the  set
                  builtin command); the -L option forces symbolic links to be fol-
                  lowed.  An argument of - is equivalent to $OLDPWD.   If  a  non-
                  empty  directory  name from CDPATH is used, or if - is the first
                  argument, and the directory change is successful,  the  absolute
                  the exit status is 0 if command was found, and  1  if  not.   If
                  neither option is supplied and an error occurred or command can-
                  not be found, the exit status is 127.  Otherwise, the exit  sta-
                  tus of the command builtin is the exit status of command.
    
           compgen [option] [word]
                  Generate  possible  completion matches for word according to the
                  options, which may  be  any  option  accepted  by  the  complete
                  builtin  with  the exception of -p and -r, and write the matches
                  to the standard output.  When using the -F or  -C  options,  the
                  various  shell  variables  set  by  the  programmable completion
                  facilities, while available, will not have useful values.
    
                  The matches will be generated in the same way  as  if  the  pro-
                  grammable  completion  code  had  generated them directly from a
                  completion specification with the same flags.  If word is speci-
                  fied, only those completions matching word will be displayed.
    
                  The  return  value is true unless an invalid option is supplied,
                  or no matches were generated.
    
           complete [-abcdefgjksuv] [-o comp-option] [-DE] [-A action]  [-G  glob-
           pat] [-W wordlist] [-F function] [-C command]
                  [-X filterpat] [-P prefix] [-S suffix] name [name ...]
           complete -pr [-DE] [name ...]
                  Specify how arguments to each name should be completed.  If  the
                  -p  option  is supplied, or if no options are supplied, existing
                  completion specifications are printed in a way that allows  them
                  to be reused as input.  The -r option removes a completion spec-
                  ification for each name, or, if no names are supplied, all  com-
                  pletion  specifications.   The  -D  option  indicates  that  the
                  remaining options and actions should apply  to  the  ''default''
                  command  completion;  that is, completion attempted on a command
                  for which no completion has previously  been  defined.   The  -E
                  option  indicates  that the remaining options and actions should
                  apply to  ''empty''  command  completion;  that  is,  completion
                  attempted on a blank line.
    
                  The  process  of  applying  these completion specifications when
                  word completion is  attempted  is  described  above  under  Pro-
                  grammable Completion.
    
                  Other  options,  if specified, have the following meanings.  The
                  arguments to the -G, -W, and -X options (and, if necessary,  the
                  -P  and -S options) should be quoted to protect them from expan-
                  sion before the complete builtin is invoked.
                  -o comp-option
                          The comp-option controls several aspects  of  the  comp-
                          spec's  behavior beyond the simple generation of comple-
                          tions.  comp-option may be one of:
                          bashdefault
                                  Perform the rest of the default bash completions
                                  default)  to  words  completed at the end of the
                                  line.
                          plusdirs
                                  After any matches defined by  the  compspec  are
                                  generated,    directory   name   completion   is
                                  attempted and  any  matches  are  added  to  the
                                  results of the other actions.
                  -A action
                          The  action  may  be  one of the following to generate a
                          list of possible completions:
                          alias   Alias names.  May also be specified as -a.
                          arrayvar
                                  Array variable names.
                          binding Readline key binding names.
                          builtin Names of shell builtin commands.   May  also  be
                                  specified as -b.
                          command Command names.  May also be specified as -c.
                          directory
                                  Directory names.  May also be specified as -d.
                          disabled
                                  Names of disabled shell builtins.
                          enabled Names of enabled shell builtins.
                          export  Names  of exported shell variables.  May also be
                                  specified as -e.
                          file    File names.  May also be specified as -f.
                          function
                                  Names of shell functions.
                          group   Group names.  May also be specified as -g.
                          helptopic
                                  Help topics as accepted by the help builtin.
                          hostname
                                  Hostnames, as taken from the file  specified  by
                                  the HOSTFILE shell variable.
                          job     Job  names,  if job control is active.  May also
                                  be specified as -j.
                          keyword Shell reserved words.  May also be specified  as
                                  -k.
                          running Names of running jobs, if job control is active.
                          service Service names.  May also be specified as -s.
                          setopt  Valid arguments for the -o  option  to  the  set
                                  builtin.
                          shopt   Shell  option  names  as  accepted  by the shopt
                                  builtin.
                          signal  Signal names.
                          stopped Names of stopped jobs, if job control is active.
                          user    User names.  May also be specified as -u.
                          variable
                                  Names of all shell variables.  May also be spec-
                                  ified as -v.
                  -G globpat
                          The pathname expansion pattern globpat  is  expanded  to
                          generate the possible completions.
    
                  -X filterpat
                          filterpat  is  a pattern as used for pathname expansion.
                          It is applied to the list of possible completions gener-
                          ated  by  the  preceding options and arguments, and each
                          completion matching filterpat is removed from the  list.
                          A  leading  !  in filterpat negates the pattern; in this
                          case, any completion not matching filterpat is  removed.
                  -P prefix
                          prefix  is  added at the beginning of each possible com-
                          pletion after all other options have been applied.
                  -S suffix
                          suffix is appended to each possible completion after all
                          other options have been applied.
    
                  The  return  value is true unless an invalid option is supplied,
                  an option other than -p or -r is supplied without a  name  argu-
                  ment,  an  attempt  is made to remove a completion specification
                  for a name for which no specification exists, or an error occurs
                  adding a completion specification.
    
           compopt [-o option] [-DE] [+o option] [name]
                  Modify  completion  options  for  each  name  according  to  the
                  options, or for the currently-execution completion if  no  names
                  are  supplied.   If no options are given, display the completion
                  options for each name or the current completion.   The  possible
                  values  of  option  are  those  valid  for  the complete builtin
                  described above.  The -D option  indicates  that  the  remaining
                  options should apply to the ''default'' command completion; that
                  is, completion attempted on a command for  which  no  completion
                  has  previously  been defined.  The -E option indicates that the
                  remaining options should apply to ''empty'' command  completion;
                  that is, completion attempted on a blank line.
    
           The  return  value  is  true  unless  an invalid option is supplied, an
           attempt is made to modify the options for a name for which  no  comple-
           tion specification exists, or an output error occurs.
    
           continue [n]
                  Resume the next iteration of the enclosing for, while, until, or
                  select loop.  If n is specified, resume  at  the  nth  enclosing
                  loop.   n  must  be  >=  1.   If  n is greater than the number of
                  enclosing loops, the  last  enclosing  loop  (the  ''top-level''
                  loop) is resumed.  When continue is executed inside of loop, the
                  return value is non-zero when n  is  <=  0;  Otherwise,  continue
                  returns  0 value. When continue is executed outside of loop, the
                  return value is 0.
    
           declare [-aAfFilrtux] [-p] [name[=value] ...]
           typeset [-aAfFilrtux] [-p] [name[=value] ...]
                  Declare variables and/or give them attributes.  If no names  are
                  given  then display the values of variables.  The -p option will
                  display the attributes and values of each name.  When -p is used
                         above).
                  -A     Each name is an associative array  variable  (see  Arrays
                         above).
                  -f     Use function names only.
                  -i     The variable is treated as an integer; arithmetic evalua-
                         tion (see ARITHMETIC EVALUATION above) is performed  when
                         the variable is assigned a value.
                  -l     When  the  variable  is  assigned a value, all upper-case
                         characters are converted to lower-case.   The  upper-case
                         attribute is disabled.
                  -r     Make names readonly.  These names cannot then be assigned
                         values by subsequent assignment statements or unset.
                  -t     Give each name the  trace  attribute.   Traced  functions
                         inherit  the  DEBUG  and  RETURN  traps  from the calling
                         shell.  The trace attribute has no  special  meaning  for
                         variables.
                  -u     When  the  variable  is  assigned a value, all lower-case
                         characters are converted to upper-case.   The  lower-case
                         attribute is disabled.
                  -x     Mark  names  for  export  to  subsequent commands via the
                         environment.
    
                  Using '+' instead of '-' turns off the attribute  instead,  with
                  the exceptions that +a may not be used to destroy an array vari-
                  able and +r will not remove the readonly attribute.   When  used
                  in a function, makes each name local, as with the local command.
                  If a variable name is followed by =value, the value of the vari-
                  able  is  set to value.  The return value is 0 unless an invalid
                  option is encountered, an attempt is made to define  a  function
                  using  ''-f foo=bar'', an attempt is made to assign a value to a
                  readonly variable, an attempt is made to assign a  value  to  an
                  array variable without using the compound assignment syntax (see
                  Arrays above), one of the names is not a  valid  shell  variable
                  name, an attempt is made to turn off readonly status for a read-
                  only variable, an attempt is made to turn off array  status  for
                  an  array variable, or an attempt is made to display a non-exis-
                  tent function with -f.
    
           dirs [+n] [-n] [-cplv]
                  Without options,  displays  the  list  of  currently  remembered
                  directories.   The  default  display  is  on  a single line with
                  directory names separated by spaces.  Directories are  added  to
                  the  list  with  the  pushd  command;  the  popd command removes
                  entries from the list.
                  +n     Displays the nth entry counting from the left of the list
                         shown by dirs when invoked without options, starting with
                         zero.
                  -n     Displays the nth entry counting from  the  right  of  the
                         list shown by dirs when invoked without options, starting
                         with zero.
                  -c     Clears  the  directory  stack  by  deleting  all  of  the
                         entries.
    
                  ble, but is marked so that SIGHUP is not sent to the job if  the
                  shell  receives a SIGHUP.  If no jobspec is present, and neither
                  the -a nor the -r option is supplied, the current job  is  used.
                  If no jobspec is supplied, the -a option means to remove or mark
                  all jobs; the -r option without  a  jobspec  argument  restricts
                  operation  to running jobs.  The return value is 0 unless a job-
                  spec does not specify a valid job.
    
           echo [-neE] [arg ...]
                  Output the args, separated by spaces,  followed  by  a  newline.
                  The return status is always 0.  If -n is specified, the trailing
                  newline is suppressed.  If the -e option is  given,  interpreta-
                  tion  of  the following backslash-escaped characters is enabled.
                  The -E option disables the interpretation of these escape  char-
                  acters,  even  on systems where they are interpreted by default.
                  The xpg_echo shell option may be used to  dynamically  determine
                  whether  or not echo expands these escape characters by default.
                  echo does not interpret -- to mean the  end  of  options.   echo
                  interprets the following escape sequences:
                  \a     alert (bell)
                  \b     backspace
                  \c     suppress further output
                  \e     an escape character
                  \f     form feed
                  \n     new line
                  \r     carriage return
                  \t     horizontal tab
                  \v     vertical tab
                  \\     backslash
                  \0nnn  the  eight-bit  character  whose value is the octal value
                         nnn (zero to three octal digits)
                  \xHH   the eight-bit character whose value  is  the  hexadecimal
                         value HH (one or two hex digits)
    
           enable [-a] [-dnps] [-f filename] [name ...]
                  Enable  and disable builtin shell commands.  Disabling a builtin
                  allows a disk command which has the same name as a shell builtin
                  to  be  executed without specifying a full pathname, even though
                  the shell normally searches for builtins before  disk  commands.
                  If  -n  is  used,  each  name  is disabled; otherwise, names are
                  enabled.  For example, to use the test binary found via the PATH
                  instead  of  the  shell builtin version, run ''enable -n test''.
                  The -f option means to load the new builtin  command  name  from
                  shared object filename, on systems that support dynamic loading.
                  The -d option will delete a builtin previously loaded  with  -f.
                  If no name arguments are given, or if the -p option is supplied,
                  a list of shell builtins is printed.  With no other option argu-
                  ments,  the  list consists of all enabled shell builtins.  If -n
                  is supplied, only disabled builtins are printed.  If -a is  sup-
                  plied,  the  list printed includes all builtins, with an indica-
                  tion of whether or not each is enabled.  If -s is supplied,  the
                  output  is restricted to the POSIX special builtins.  The return
                  login(1) does.  The -c option causes command to be executed with
                  an  empty environment.  If -a is supplied, the shell passes name
                  as the zeroth argument to the executed command.  If command can-
                  not  be executed for some reason, a non-interactive shell exits,
                  unless the shell option execfail is enabled, in  which  case  it
                  returns  failure.   An  interactive shell returns failure if the
                  file cannot be executed.  If command is not specified, any redi-
                  rections take effect in the current shell, and the return status
                  is 0.  If there is a redirection error, the return status is  1.
    
           exit [n]
                  Cause  the  shell  to exit with a status of n.  If n is omitted,
                  the exit status is that of the last command executed.  A trap on
                  EXIT is executed before the shell terminates.
    
           export [-fn] [name[=word]] ...
           export -p
                  The  supplied names are marked for automatic export to the envi-
                  ronment of subsequently executed commands.  If the -f option  is
                  given,  the names refer to functions.  If no names are given, or
                  if the -p option is supplied, a  list  of  all  names  that  are
                  exported  in  this  shell  is printed.  The -n option causes the
                  export property to be removed from each  name.   If  a  variable
                  name  is  followed by =word, the value of the variable is set to
                  word.  export returns an exit status  of  0  unless  an  invalid
                  option  is  encountered,  one  of the names is not a valid shell
                  variable name, or -f is supplied with a name that is not a func-
                  tion.
    
           fc [-e ename] [-lnr] [first] [last]
           fc -s [pat=rep] [cmd]
                  Fix  Command.  In the first form, a range of commands from first
                  to last is selected from the history list.  First and  last  may
                  be  specified  as a string (to locate the last command beginning
                  with that string) or as a number  (an  index  into  the  history
                  list, where a negative number is used as an offset from the cur-
                  rent command number).  If last is not specified it is set to the
                  current  command  for  listing (so that ''fc -l -10'' prints the
                  last 10 commands) and to first otherwise.  If first is not spec-
                  ified  it is set to the previous command for editing and -16 for
                  listing.
    
                  The -n option suppresses the command numbers when listing.   The
                  -r  option reverses the order of the commands.  If the -l option
                  is given, the commands are listed on  standard  output.   Other-
                  wise,  the editor given by ename is invoked on a file containing
                  those commands.  If ename is not given, the value of the  FCEDIT
                  variable  is used, and the value of EDITOR if FCEDIT is not set.
                  If neither variable is set, vi is used.  When  editing  is  com-
                  plete, the edited commands are echoed and executed.
    
                  In  the  second form, command is re-executed after each instance
    
           fg [jobspec]
                  Resume jobspec in the foreground, and make it the  current  job.
                  If jobspec is not present, the shell's notion of the current job
                  is used.  The return value is that of the  command  placed  into
                  the  foreground,  or failure if run when job control is disabled
                  or, when run with job control enabled, if jobspec does not spec-
                  ify  a  valid  job  or  jobspec specifies a job that was started
                  without job control.
    
           getopts optstring name [args]
                  getopts is used by shell procedures to parse positional  parame-
                  ters.   optstring  contains  the  option characters to be recog-
                  nized; if a character is followed by  a  colon,  the  option  is
                  expected  to have an argument, which should be separated from it
                  by white space.  The colon and question mark characters may  not
                  be  used as option characters.  Each time it is invoked, getopts
                  places the next option in the shell variable name,  initializing
                  name if it does not exist, and the index of the next argument to
                  be processed into the variable OPTIND.  OPTIND is initialized to
                  1  each  time  the  shell or a shell script is invoked.  When an
                  option requires an argument, getopts places that  argument  into
                  the  variable OPTARG.  The shell does not reset OPTIND automati-
                  cally; it must be  manually  reset  between  multiple  calls  to
                  getopts within the same shell invocation if a new set of parame-
                  ters is to be used.
    
                  When the end of options is encountered,  getopts  exits  with  a
                  return  value  greater than zero.  OPTIND is set to the index of
                  the first non-option argument, and name is set to ?.
    
                  getopts normally parses the positional parameters, but  if  more
                  arguments are given in args, getopts parses those instead.
    
                  getopts  can  report errors in two ways.  If the first character
                  of optstring is a colon, silent error  reporting  is  used.   In
                  normal  operation  diagnostic  messages are printed when invalid
                  options or missing option arguments  are  encountered.   If  the
                  variable  OPTERR  is  set  to  0, no error messages will be dis-
                  played, even if the first character of optstring is not a colon.
    
                  If an invalid option is seen, getopts places ? into name and, if
                  not silent, prints an  error  message  and  unsets  OPTARG.   If
                  getopts  is  silent,  the  option  character  found is placed in
                  OPTARG and no diagnostic message is printed.
    
                  If a required argument is not found, and getopts is not  silent,
                  a  question  mark  (?) is placed in name, OPTARG is unset, and a
                  diagnostic message is printed.  If getopts  is  silent,  then  a
                  colon  (:)  is  placed  in  name and OPTARG is set to the option
                  character found.
    
                  getopts returns true if an option, specified or unspecified,  is
                  mat that may be reused as input.  If no arguments are given,  or
                  if only -l is supplied, information about remembered commands is
                  printed.  The return status is true unless a name is  not  found
                  or an invalid option is supplied.
    
           help [-dms] [pattern]
                  Display  helpful information about builtin commands.  If pattern
                  is specified, help gives detailed help on all commands  matching
                  pattern;  otherwise  help for all the builtins and shell control
                  structures is printed.
                  -d     Display a short description of each pattern
                  -m     Display the description of each pattern in a manpage-like
                         format
                  -s     Display only a short usage synopsis for each pattern
           The return status is 0 unless no command matches pattern.
    
           history [n]
           history -c
           history -d offset
           history -anrw [filename]
           history -p arg [arg ...]
           history -s arg [arg ...]
                  With no options, display the command history list with line num-
                  bers.  Lines listed with a * have been modified.  An argument of
                  n  lists only the last n lines.  If the shell variable HISTTIME-
                  FORMAT is set and not null, it is used as a  format  string  for
                  strftime(3)  to display the time stamp associated with each dis-
                  played history entry.  No intervening blank is  printed  between
                  the  formatted  time stamp and the history line.  If filename is
                  supplied, it is used as the name of the history  file;  if  not,
                  the  value  of HISTFILE is used.  Options, if supplied, have the
                  following meanings:
                  -c     Clear the history list by deleting all the entries.
                  -d offset
                         Delete the history entry at position offset.
                  -a     Append the ''new'' history lines (history  lines  entered
                         since  the  beginning of the current bash session) to the
                         history file.
                  -n     Read the history lines not already read from the  history
                         file  into  the  current  history  list.  These are lines
                         appended to the history file since the beginning  of  the
                         current bash session.
                  -r     Read the contents of the history file and use them as the
                         current history.
                  -w     Write the current history to the history file,  overwrit-
                         ing the history file's contents.
                  -p     Perform  history  substitution  on the following args and
                         display the result on  the  standard  output.   Does  not
                         store  the results in the history list.  Each arg must be
                         quoted to disable normal history expansion.
                  -s     Store the args in the history list  as  a  single  entry.
                         The  last  command  in the history list is removed before
    
           jobs -x command [ args ... ]
                  The first form lists the active jobs.  The options have the fol-
                  lowing meanings:
                  -l     List process IDs in addition to the normal information.
                  -p     List only the process  ID  of  the  job's  process  group
                         leader.
                  -n     Display  information  only  about  jobs that have changed
                         status since the user was last notified of their  status.
                  -r     Restrict output to running jobs.
                  -s     Restrict output to stopped jobs.
    
                  If  jobspec  is given, output is restricted to information about
                  that job.  The return status is 0 unless an  invalid  option  is
                  encountered or an invalid jobspec is supplied.
    
                  If the -x option is supplied, jobs replaces any jobspec found in
                  command or args with the corresponding  process  group  ID,  and
                  executes command passing it args, returning its exit status.
    
           kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
           kill -l [sigspec | exit_status]
                  Send  the  signal  named  by  sigspec or signum to the processes
                  named by pid or jobspec.  sigspec is either  a  case-insensitive
                  signal  name such as SIGKILL (with or without the SIG prefix) or
                  a signal number; signum is a signal number.  If sigspec  is  not
                  present,  then  SIGTERM is assumed.  An argument of -l lists the
                  signal names.  If any arguments are supplied when -l  is  given,
                  the  names  of  the  signals  corresponding to the arguments are
                  listed, and the return status is 0.  The exit_status argument to
                  -l  is  a  number  specifying either a signal number or the exit
                  status of a process terminated by a signal.  kill  returns  true
                  if  at  least  one  signal was successfully sent, or false if an
                  error occurs or an invalid option is encountered.
    
           let arg [arg ...]
                  Each arg is an arithmetic expression to be evaluated (see ARITH-
                  METIC  EVALUATION  above).   If the last arg evaluates to 0, let
                  returns 1; 0 is returned otherwise.
    
           local [option] [name[=value] ...]
                  For each argument, a local variable named name is  created,  and
                  assigned  value.   The option can be any of the options accepted
                  by declare.  When local is used within a function, it causes the
                  variable  name  to have a visible scope restricted to that func-
                  tion and its children.  With no operands, local writes a list of
                  local  variables  to the standard output.  It is an error to use
                  local when not within a function.  The return status is 0 unless
                  local  is  used outside a function, an invalid name is supplied,
                  or name is a readonly variable.
    
           logout Exit a login shell.
    
                  -u     Read  lines  from file descriptor fd instead of the stan-
                         dard input.
                  -C     Evaluate callback each time quantum lines are read.   The
                         -c option specifies quantum.
                  -c     Specify  the  number  of  lines read between each call to
                         callback.
    
                  If -C is specified without -c,  the  default  quantum  is  5000.
                  When callback is evaluated, it is supplied the index of the next
                  array element to be assigned as an additional  argument.   call-
                  back  is  evaluated  after the line is read but before the array
                  element is assigned.
    
                  If not supplied with an  explicit  origin,  mapfile  will  clear
                  array before assigning to it.
    
                  mapfile  returns successfully unless an invalid option or option
                  argument is supplied, array is invalid or  unassignable,  or  if
                  array is not an indexed array.
    
           popd [-n] [+n] [-n]
                  Removes  entries  from  the directory stack.  With no arguments,
                  removes the top directory from the stack, and performs a  cd  to
                  the new top directory.  Arguments, if supplied, have the follow-
                  ing meanings:
                  -n     Suppresses the normal change of directory  when  removing
                         directories  from  the  stack,  so that only the stack is
                         manipulated.
                  +n     Removes the nth entry counting from the left of the  list
                         shown  by  dirs, starting with zero.  For example: ''popd
                         +0'' removes the first directory, ''popd +1'' the second.
                  -n     Removes the nth entry counting from the right of the list
                         shown by dirs, starting with zero.  For  example:  ''popd
                         -0''  removes the last directory, ''popd -1'' the next to
                         last.
    
                  If the popd command is successful, a dirs is performed as  well,
                  and  the  return  status is 0.  popd returns false if an invalid
                  option is encountered, the directory stack is empty, a non-exis-
                  tent directory stack entry is specified, or the directory change
                  fails.
    
           printf [-v var] format [arguments]
                  Write the formatted arguments to the standard output  under  the
                  control  of  the format.  The format is a character string which
                  contains three types of objects:  plain  characters,  which  are
                  simply  copied  to  standard output, character escape sequences,
                  which are converted and copied to the standard output, and  for-
                  mat  specifications,  each  of which causes printing of the next
                  successive argument.  In addition to the standard printf(1) for-
                  mats,  %b  causes printf to expand backslash escape sequences in
                  the corresponding argument (except that  \c  terminates  output,
    
           pushd [-n] [+n] [-n]
           pushd [-n] [dir]
                  Adds  a  directory to the top of the directory stack, or rotates
                  the stack, making the new top of the stack the  current  working
                  directory.  With no arguments, exchanges the top two directories
                  and returns 0, unless the directory stack is empty.   Arguments,
                  if supplied, have the following meanings:
                  -n     Suppresses  the  normal  change  of directory when adding
                         directories to the stack,  so  that  only  the  stack  is
                         manipulated.
                  +n     Rotates  the  stack  so  that the nth directory (counting
                         from the left of the list shown by  dirs,  starting  with
                         zero) is at the top.
                  -n     Rotates  the  stack  so  that the nth directory (counting
                         from the right of the list shown by dirs,  starting  with
                         zero) is at the top.
                  dir    Adds dir to the directory stack at the top, making it the
                         new current working directory.
    
                  If the pushd command is successful, a dirs is performed as well.
                  If  the first form is used, pushd returns 0 unless the cd to dir
                  fails.  With the second form, pushd returns 0 unless the  direc-
                  tory  stack  is empty, a non-existent directory stack element is
                  specified, or the directory change to the specified new  current
                  directory fails.
    
           pwd [-LP]
                  Print  the  absolute  pathname of the current working directory.
                  The pathname printed contains no symbolic links if the -P option
                  is supplied or the -o physical option to the set builtin command
                  is enabled.  If the -L option is used, the pathname printed  may
                  contain  symbolic links.  The return status is 0 unless an error
                  occurs while reading the name of the  current  directory  or  an
                  invalid option is supplied.
    
           read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p
           prompt] [-t timeout] [-u fd] [name ...]
                  One  line  is  read  from  the  standard input, or from the file
                  descriptor fd supplied as an argument to the -u option, and  the
                  first word is assigned to the first name, the second word to the
                  second name, and so on, with leftover words and their  interven-
                  ing  separators  assigned  to the last name.  If there are fewer
                  words read from the input stream than names, the remaining names
                  are  assigned  empty  values.  The characters in IFS are used to
                  split the line into words.  The backslash character (\)  may  be
                  used  to  remove any special meaning for the next character read
                  and for line continuation.  Options, if supplied, have the  fol-
                  lowing meanings:
                  -a aname
                         The words are assigned to sequential indices of the array
                         variable aname, starting at 0.  aname is unset before any
                         new  values  are  assigned.   Other  name  arguments  are
                         iter  if fewer than nchars characters are read before the
                         delimiter.
                  -N nchars
                         read returns  after  reading  exactly  nchars  characters
                         rather  than waiting for a complete line of input, unless
                         EOF is encountered or read times out.  Delimiter  charac-
                         ters  encountered  in the input are not treated specially
                         and do not cause read to return until  nchars  characters
                         are read.
                  -p prompt
                         Display prompt on standard error, without a trailing new-
                         line, before attempting to read any input.  The prompt is
                         displayed only if input is coming from a terminal.
                  -r     Backslash does not act as an escape character.  The back-
                         slash is considered to be part of the line.  In  particu-
                         lar,  a  backslash-newline pair may not be used as a line
                         continuation.
                  -s     Silent mode.  If input is coming from a terminal, charac-
                         ters are not echoed.
                  -t timeout
                         Cause  read  to time out and return failure if a complete
                         line of input is not read within timeout seconds.   time-
                         out  may  be  a  decimal number with a fractional portion
                         following the decimal point.  This option is only  effec-
                         tive  if  read is reading input from a terminal, pipe, or
                         other special file; it has no effect  when  reading  from
                         regular  files.  If timeout is 0, read returns success if
                         input is available  on  the  specified  file  descriptor,
                         failure  otherwise.   The exit status is greater than 128
                         if the timeout is exceeded.
                  -u fd  Read input from file descriptor fd.
    
                  If no names are supplied, the line read is assigned to the vari-
                  able  REPLY.   The  return  code  is zero, unless end-of-file is
                  encountered, read times out (in which case the  return  code  is
                  greater  than 128), or an invalid file descriptor is supplied as
                  the argument to -u.
    
           readonly [-aApf] [name[=word] ...]
                  The given names are marked readonly; the values of  these  names
                  may  not  be changed by subsequent assignment.  If the -f option
                  is supplied, the functions corresponding to  the  names  are  so
                  marked.   The  -a  option  restricts  the  variables  to indexed
                  arrays; the -A option restricts  the  variables  to  associative
                  arrays.   If no name arguments are given, or if the -p option is
                  supplied, a list of all  readonly  names  is  printed.   The  -p
                  option  causes  output  to  be displayed in a format that may be
                  reused as input.  If a variable name is followed by  =word,  the
                  value  of  the  variable is set to word.  The return status is 0
                  unless an invalid option is encountered, one of the names is not
                  a  valid shell variable name, or -f is supplied with a name that
                  is not a function.
    
           set [+abefhkmnptuvxBCEHPT] [+o option] [arg ...]
                  Without options, the name and value of each shell  variable  are
                  displayed in a format that can be reused as input for setting or
                  resetting the currently-set variables.  Read-only variables can-
                  not  be  reset.  In posix mode, only shell variables are listed.
                  The output is sorted according  to  the  current  locale.   When
                  options  are specified, they set or unset shell attributes.  Any
                  arguments remaining after option processing are treated as  val-
                  ues for the positional parameters and are assigned, in order, to
                  $1, $2, ...  $n.  Options,  if  specified,  have  the  following
                  meanings:
                  -a      Automatically  mark  variables  and  functions which are
                          modified or created for export  to  the  environment  of
                          subsequent commands.
                  -b      Report  the status of terminated background jobs immedi-
                          ately, rather than before the next primary prompt.  This
                          is effective only when job control is enabled.
                  -e      Exit  immediately  if a pipeline (which may consist of a
                          single simple command),  a subshell command enclosed  in
                          parentheses,  or one of the commands executed as part of
                          a command list enclosed by  braces  (see  SHELL  GRAMMAR
                          above) exits with a non-zero status.  The shell does not
                          exit if the command that fails is part  of  the  command
                          list  immediately  following  a  while or until keyword,
                          part of the test  following  the  if  or  elif  reserved
                          words,  part  of any command executed in a && or || list
                          except the command following the final  &&  or  ||,  any
                          command  in a pipeline but the last, or if the command's
                          return value is being inverted with !.  A trap  on  ERR,
                          if set, is executed before the shell exits.  This option
                          applies to the shell environment and each subshell envi-
                          ronment  separately  (see  COMMAND EXECUTION ENVIRONMENT
                          above), and may cause subshells to exit before executing
                          all the commands in the subshell.
                  -f      Disable pathname expansion.
                  -h      Remember  the location of commands as they are looked up
                          for execution.  This is enabled by default.
                  -k      All arguments in the form of assignment  statements  are
                          placed  in the environment for a command, not just those
                          that precede the command name.
                  -m      Monitor mode.  Job control is enabled.  This  option  is
                          on  by  default  for  interactive shells on systems that
                          support it (see JOB  CONTROL  above).   Background  pro-
                          cesses  run  in a separate process group and a line con-
                          taining their exit status is printed upon their  comple-
                          tion.
                  -n      Read commands but do not execute them.  This may be used
                          to check a shell script  for  syntax  errors.   This  is
                          ignored by interactive shells.
                  -o option-name
                          The option-name can be one of the following:
                          allexport
                          histexpand
                                  Same as -H.
                          history Enable command history, as described above under
                                  HISTORY.  This option is on by default in inter-
                                  active shells.
                          ignoreeof
                                  The   effect   is   as   if  the  shell  command
                                  ''IGNOREEOF=10'' had been  executed  (see  Shell
                                  Variables above).
                          keyword Same as -k.
                          monitor Same as -m.
                          noclobber
                                  Same as -C.
                          noexec  Same as -n.
                          noglob  Same as -f.
                          nolog   Currently ignored.
                          notify  Same as -b.
                          nounset Same as -u.
                          onecmd  Same as -t.
                          physical
                                  Same as -P.
                          pipefail
                                  If  set,  the  return value of a pipeline is the
                                  value of the last (rightmost)  command  to  exit
                                  with  a non-zero status, or zero if all commands
                                  in the pipeline exit successfully.  This  option
                                  is disabled by default.
                          posix   Change  the  behavior  of bash where the default
                                  operation differs from  the  POSIX  standard  to
                                  match the standard (posix mode).
                          privileged
                                  Same as -p.
                          verbose Same as -v.
                          vi      Use  a  vi-style command line editing interface.
                                  This also affects the editing interface used for
                                  read -e.
                          xtrace  Same as -x.
                          If -o is supplied with no option-name, the values of the
                          current options are printed.  If +o is supplied with  no
                          option-name,  a  series  of set commands to recreate the
                          current option settings is  displayed  on  the  standard
                          output.
                  -p      Turn  on  privileged  mode.   In this mode, the $ENV and
                          $BASH_ENV files are not processed, shell  functions  are
                          not  inherited  from the environment, and the SHELLOPTS,
                          BASHOPTS, CDPATH,  and  GLOBIGNORE  variables,  if  they
                          appear in the environment, are ignored.  If the shell is
                          started with the effective user (group) id not equal  to
                          the  real user (group) id, and the -p option is not sup-
                          plied, these actions are taken and the effective user id
                          is  set  to  the real user id.  If the -p option is sup-
                          plied at startup, the effective user id  is  not  reset.
    
                  -B      The shell performs brace expansion (see Brace  Expansion
                          above).  This is on by default.
                  -C      If  set,  bash  does not overwrite an existing file with
                          the >, >&, and <> redirection operators.   This  may  be
                          overridden when creating output files by using the redi-
                          rection operator >| instead of >.
                  -E      If set, any trap on ERR is inherited by shell functions,
                          command  substitutions,  and commands executed in a sub-
                          shell environment.  The ERR trap is normally not  inher-
                          ited in such cases.
                  -H      Enable !  style history substitution.  This option is on
                          by default when the shell is interactive.
                  -P      If set, the shell does not follow  symbolic  links  when
                          executing  commands  such  as cd that change the current
                          working  directory.   It  uses  the  physical  directory
                          structure instead.  By default, bash follows the logical
                          chain of  directories  when  performing  commands  which
                          change the current directory.
                  -T      If  set,  any traps on DEBUG and RETURN are inherited by
                          shell functions,  command  substitutions,  and  commands
                          executed  in  a  subshell  environment.   The  DEBUG and
                          RETURN traps are normally not inherited in such cases.
                  --      If no arguments follow this option, then the  positional
                          parameters are unset.  Otherwise, the positional parame-
                          ters are set to the args, even if  some  of  them  begin
                          with a -.
                  -       Signal  the  end of options, cause all remaining args to
                          be assigned to the positional parameters.  The -x and -v
                          options are turned off.  If there are no args, the posi-
                          tional parameters remain unchanged.
    
                  The options are off by default unless otherwise noted.  Using  +
                  rather  than  -  causes  these  options  to  be turned off.  The
                  options can also be specified as arguments to an  invocation  of
                  the  shell.  The current set of options may be found in $-.  The
                  return status is always true unless an invalid option is encoun-
                  tered.
    
           shift [n]
                  The  positional  parameters  from n+1 ... are renamed to $1 ....
                  Parameters represented by the numbers  $#  down  to  $#-n+1  are
                  unset.   n  must  be a non-negative number less than or equal to
                  $#.  If n is 0, no parameters are changed.  If n is  not  given,
                  it  is assumed to be 1.  If n is greater than $#, the positional
                  parameters are not changed.  The return status is  greater  than
                  zero if n is greater than $# or less than zero; otherwise 0.
    
           shopt [-pqsu] [-o] [optname ...]
                  Toggle the values of variables controlling optional shell behav-
                  ior.  With no options, or with the -p option, a list of all set-
                  table options is displayed, with an indication of whether or not
                  each is set.  The -p option causes output to be displayed  in  a
                  tively.   Unless otherwise noted, the shopt options are disabled
                  (unset) by default.
    
                  The return status when listing options is zero if  all  optnames
                  are  enabled,  non-zero  otherwise.   When  setting or unsetting
                  options, the return status is zero unless an optname  is  not  a
                  valid shell option.
    
                  The list of shopt options is:
    
                  autocd  If  set,  a command name that is the name of a directory
                          is executed as if it were the argument to  the  cd  com-
                          mand.  This option is only used by interactive shells.
                  cdable_vars
                          If  set,  an  argument to the cd builtin command that is
                          not a directory is assumed to be the name of a  variable
                          whose value is the directory to change to.
                  cdspell If set, minor errors in the spelling of a directory com-
                          ponent in a cd command will be  corrected.   The  errors
                          checked for are transposed characters, a missing charac-
                          ter, and one character too many.   If  a  correction  is
                          found,  the corrected file name is printed, and the com-
                          mand proceeds.  This option is only used by  interactive
                          shells.
                  checkhash
                          If set, bash checks that a command found in the hash ta-
                          ble exists before trying to execute  it.   If  a  hashed
                          command  no  longer exists, a normal path search is per-
                          formed.
                  checkjobs
                          If set, bash lists the status of any stopped and running
                          jobs  before  exiting an interactive shell.  If any jobs
                          are running, this causes the exit to be deferred until a
                          second  exit is attempted without an intervening command
                          (see JOB CONTROL above).   The  shell  always  postpones
                          exiting if any jobs are stopped.
                  checkwinsize
                          If  set,  bash checks the window size after each command
                          and, if necessary,  updates  the  values  of  LINES  and
                          COLUMNS.
                  cmdhist If  set,  bash attempts to save all lines of a multiple-
                          line command in the same  history  entry.   This  allows
                          easy re-editing of multi-line commands.
                  compat31
                          If set, bash changes its behavior to that of version 3.1
                          with respect to  quoted  arguments  to  the  conditional
                          command's =~ operator.
                  compat32
                          If set, bash changes its behavior to that of version 3.2
                          with respect to locale-specific string  comparison  when
                          using the conditional command's < and > operators.
                  compat40
                          exit if exec fails.
                  expand_aliases
                          If set, aliases are expanded as  described  above  under
                          ALIASES.  This option is enabled by default for interac-
                          tive shells.
                  extdebug
                          If set,  behavior  intended  for  use  by  debuggers  is
                          enabled:
                          1.     The -F option to the declare builtin displays the
                                 source file name and line number corresponding to
                                 each function name supplied as an argument.
                          2.     If  the  command  run by the DEBUG trap returns a
                                 non-zero value, the next command is  skipped  and
                                 not executed.
                          3.     If  the  command  run by the DEBUG trap returns a
                                 value of 2, and the shell is executing in a  sub-
                                 routine  (a shell function or a shell script exe-
                                 cuted by the . or source  builtins),  a  call  to
                                 return is simulated.
                          4.     BASH_ARGC  and BASH_ARGV are updated as described
                                 in their descriptions above.
                          5.     Function tracing is enabled:   command  substitu-
                                 tion, shell functions, and subshells invoked with
                                 ( command ) inherit the DEBUG and RETURN traps.
                          6.     Error tracing is enabled:  command  substitution,
                                 shell  functions,  and  subshells  invoked with (
                                 command ) inherit the ERROR trap.
                  extglob If set, the extended pattern matching features described
                          above under Pathname Expansion are enabled.
                  extquote
                          If  set,  $'string'  and  $"string" quoting is performed
                          within  ${parameter}  expansions  enclosed   in   double
                          quotes.  This option is enabled by default.
                  failglob
                          If  set,  patterns  which fail to match filenames during
                          pathname expansion result in an expansion error.
                  force_fignore
                          If set, the suffixes  specified  by  the  FIGNORE  shell
                          variable  cause words to be ignored when performing word
                          completion even if the ignored words are the only possi-
                          ble  completions.   See  SHELL  VARIABLES  above  for  a
                          description of  FIGNORE.   This  option  is  enabled  by
                          default.
                  globstar
                          If set, the pattern ** used in a pathname expansion con-
                          text will match a files and zero or more directories and
                          subdirectories.  If the pattern is followed by a /, only
                          directories and subdirectories match.
                  gnu_errfmt
                          If set, shell error messages are written in the standard
                          GNU error message format.
                  histappend
                          perform  hostname  completion when a word containing a @
                          is  being  completed  (see  Completing  under   READLINE
                          above).  This is enabled by default.
                  huponexit
                          If set, bash will send SIGHUP to all jobs when an inter-
                          active login shell exits.
                  interactive_comments
                          If set, allow a word beginning with # to cause that word
                          and  all remaining characters on that line to be ignored
                          in an interactive  shell  (see  COMMENTS  above).   This
                          option is enabled by default.
                  lithist If  set,  and  the cmdhist option is enabled, multi-line
                          commands are saved to the history with embedded newlines
                          rather than using semicolon separators where possible.
                  login_shell
                          The  shell  sets this option if it is started as a login
                          shell (see INVOCATION above).   The  value  may  not  be
                          changed.
                  mailwarn
                          If  set,  and  a file that bash is checking for mail has
                          been accessed since the last time it  was  checked,  the
                          message  ''The  mail in mailfile has been read'' is dis-
                          played.
                  no_empty_cmd_completion
                          If set, and  readline  is  being  used,  bash  will  not
                          attempt to search the PATH for possible completions when
                          completion is attempted on an empty line.
                  nocaseglob
                          If set, bash matches  filenames  in  a  case-insensitive
                          fashion when performing pathname expansion (see Pathname
                          Expansion above).
                  nocasematch
                          If set, bash  matches  patterns  in  a  case-insensitive
                          fashion when performing matching while executing case or
                          [[ conditional commands.
                  nullglob
                          If set, bash allows patterns which match no  files  (see
                          Pathname  Expansion  above)  to expand to a null string,
                          rather than themselves.
                  progcomp
                          If set, the programmable completion facilities (see Pro-
                          grammable Completion above) are enabled.  This option is
                          enabled by default.
                  promptvars
                          If set, prompt strings undergo parameter expansion, com-
                          mand   substitution,  arithmetic  expansion,  and  quote
                          removal after being expanded as described  in  PROMPTING
                          above.  This option is enabled by default.
                  restricted_shell
                          The   shell  sets  this  option  if  it  is  started  in
                          restricted mode (see RESTRICTED SHELL below).  The value
                          may  not be changed.  This is not reset when the startup
    
                  Suspend the execution of this shell until it receives a  SIGCONT
                  signal. When the suspended shell is a background process, it can
                  be restarted by the fg command. For more information,  read  the
                  JOB  CONTROL  section.  The  suspend command can not suspend the
                  login shell. However, when -f option is specified, suspend  com-
                  mand  can  suspend  even  login  shell.   The return status is 0
                  unless the shell is a login shell and -f is not supplied, or  if
                  job control is not enabled.
           test expr
           [ expr ]
                  Return  a  status  of  0 or 1 depending on the evaluation of the
                  conditional expression expr.  Each operator and operand must  be
                  a  separate argument.  Expressions are composed of the primaries
                  described above under CONDITIONAL EXPRESSIONS.   test  does  not
                  accept any options, nor does it accept and ignore an argument of
                  -- as signifying the end of options.
    
                  Expressions may  be  combined  using  the  following  operators,
                  listed  in  decreasing  order  of  precedence.   The  evaluation
                  depends on the number of arguments; see below.
                  ! expr True if expr is false.
                  ( expr )
                         Returns the value of expr.  This may be used to  override
                         the normal precedence of operators.
                  expr1 -a expr2
                         True if both expr1 and expr2 are true.
                  expr1 -o expr2
                         True if either expr1 or expr2 is true.
    
                  test and [ evaluate conditional expressions using a set of rules
                  based on the number of arguments.
    
                  0 arguments
                         The expression is false.
                  1 argument
                         The expression is true if and only if the argument is not
                         null.
                  2 arguments
                         If the first argument is !, the expression is true if and
                         only if the second argument is null.  If the first  argu-
                         ment  is  one  of  the unary conditional operators listed
                         above under CONDITIONAL EXPRESSIONS,  the  expression  is
                         true if the unary test is true.  If the first argument is
                         not a valid unary conditional operator, the expression is
                         false.
                  3 arguments
                         If  the  second argument is one of the binary conditional
                         operators listed above under CONDITIONAL EXPRESSIONS, the
                         result of the expression is the result of the binary test
                         using the first and third arguments as operands.  The  -a
                         and  -o  operators  are  considered binary operators when
                         there are three arguments.  If the first argument  is  !,
    
           times  Print the accumulated user and system times for  the  shell  and
                  for processes run from the shell.  The return status is 0.
    
           trap [-lp] [[arg] sigspec ...]
                  The  command  arg  is  to  be  read  and executed when the shell
                  receives signal(s) sigspec.  If arg is absent (and  there  is  a
                  single  sigspec)  or  -,  each  specified signal is reset to its
                  original disposition (the value it  had  upon  entrance  to  the
                  shell).   If arg is the null string the signal specified by each
                  sigspec is ignored by the shell and by the commands it  invokes.
                  If  arg  is  not present and -p has been supplied, then the trap
                  commands associated with each  sigspec  are  displayed.   If  no
                  arguments  are  supplied or if only -p is given, trap prints the
                  list of commands associated with each  signal.   The  -l  option
                  causes  the shell to print a list of signal names and their cor-
                  responding numbers.   Each  sigspec  is  either  a  signal  name
                  defined  in  <signal.h>,  or  a signal number.  Signal names are
                  case insensitive and the SIG prefix is optional.
    
                  If a sigspec is EXIT (0) the command arg  is  executed  on  exit
                  from  the shell.  If a sigspec is DEBUG, the command arg is exe-
                  cuted before every simple command, for  command,  case  command,
                  select  command,  every  arithmetic  for command, and before the
                  first command executes in a shell function  (see  SHELL  GRAMMAR
                  above).   Refer to the description of the extdebug option to the
                  shopt builtin for details of its effect on the DEBUG trap.  If a
                  sigspec is RETURN, the command arg is executed each time a shell
                  function or a script executed with the . or source builtins fin-
                  ishes executing.
    
                  If a sigspec is ERR, the command arg is executed whenever a sim-
                  ple command has a non-zero exit status, subject to the following
                  conditions.   The ERR trap is not executed if the failed command
                  is part of the command list immediately  following  a  while  or
                  until  keyword,  part  of the test in an if statement, part of a
                  command executed in a && or || list, or if the command's  return
                  value  is  being  inverted via !.  These are the same conditions
                  obeyed by the errexit option.
    
                  Signals ignored upon entry to the shell cannot be trapped, reset
                  or listed.  Trapped signals that are not being ignored are reset
                  to their original values in a subshell or  subshell  environment
                  when  one is created.  The return status is false if any sigspec
                  is invalid; otherwise trap returns true.
    
           type [-aftpP] name [name ...]
                  With no options, indicate how each name would be interpreted  if
                  used as a command name.  If the -t option is used, type prints a
                  string which is one of alias,  keyword,  function,  builtin,  or
                  file  if  name  is  an  alias,  shell  reserved  word, function,
                  builtin, or disk file, respectively.  If the name is not  found,
    
           ulimit [-HSTabcdefilmnpqrstuvx [limit]]
                  Provides control over the resources available to the  shell  and
                  to  processes started by it, on systems that allow such control.
                  The -H and -S options specify that the hard or soft limit is set
                  for  the  given resource.  A hard limit cannot be increased by a
                  non-root user once it is set; a soft limit may be  increased  up
                  to  the value of the hard limit.  If neither -H nor -S is speci-
                  fied, both the soft and hard limits are set.  The value of limit
                  can be a number in the unit specified for the resource or one of
                  the special values hard, soft, or unlimited, which stand for the
                  current  hard  limit,  the  current  soft  limit,  and no limit,
                  respectively.  If limit is omitted, the  current  value  of  the
                  soft  limit  of the resource is printed, unless the -H option is
                  given.  When more than one resource is specified, the limit name
                  and unit are printed before the value.  Other options are inter-
                  preted as follows:
                  -a     All current limits are reported
                  -b     The maximum socket buffer size
                  -c     The maximum size of core files created
                  -d     The maximum size of a process's data segment
                  -e     The maximum scheduling priority ("nice")
                  -f     The maximum size of files written by the  shell  and  its
                         children
                  -i     The maximum number of pending signals
                  -l     The maximum size that may be locked into memory
                  -m     The  maximum resident set size (many systems do not honor
                         this limit)
                  -n     The maximum number of open file descriptors (most systems
                         do not allow this value to be set)
                  -p     The pipe size in 512-byte blocks (this may not be set)
                  -q     The maximum number of bytes in POSIX message queues
                  -r     The maximum real-time scheduling priority
                  -s     The maximum stack size
                  -t     The maximum amount of cpu time in seconds
                  -u     The  maximum  number  of  processes available to a single
                         user
                  -v     The maximum amount of virtual  memory  available  to  the
                         shell
                  -x     The maximum number of file locks
                  -T     The maximum number of threads
    
                  If limit is given, it is the new value of the specified resource
                  (the -a option is display only).  If no option is given, then -f
                  is  assumed.  Values are in 1024-byte increments, except for -t,
                  which is in seconds, -p, which is in units of  512-byte  blocks,
                  and  -T,  -b, -n, and -u, which are unscaled values.  The return
                  status is 0 unless an invalid option or argument is supplied, or
                  an  error  occurs  while  setting  a  new  limit.  In POSIX Mode
                  512-byte blocks are used for the '-c' and '-f' options.
    
           umask [-p] [-S] [mode]
                  is true unless a supplied name is not a defined alias.
    
           unset [-fv] [name ...]
                  For  each  name,  remove the corresponding variable or function.
                  If no options are supplied, or the -v option is given, each name
                  refers  to  a  shell  variable.   Read-only variables may not be
                  unset.  If -f is specified, each name refers to  a  shell  func-
                  tion,  and the function definition is removed.  Each unset vari-
                  able or function is removed from the environment passed to  sub-
                  sequent  commands.   If any of COMP_WORDBREAKS, RANDOM, SECONDS,
                  LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are  unset,  they
                  lose  their  special  properties,  even if they are subsequently
                  reset.  The exit status is true unless a name is readonly.
    
           wait [n ...]
                  Wait for each specified process and return its termination  sta-
                  tus.   Each  n  may be a process ID or a job specification; if a
                  job spec is given, all processes  in  that  job's  pipeline  are
                  waited  for.  If n is not given, all currently active child pro-
                  cesses are waited for, and the return  status  is  zero.   If  n
                  specifies  a  non-existent  process or job, the return status is
                  127.  Otherwise, the return status is the  exit  status  of  the
                  last process or job waited for.
    
    
    

    RESTRICTED SHELL

           If bash is started with the name rbash, or the -r option is supplied at
           invocation, the shell becomes restricted.  A restricted shell  is  used
           to  set  up an environment more controlled than the standard shell.  It
           behaves identically to bash with the exception that the  following  are
           disallowed or not performed:
    
           ?      changing directories with cd
    
           ?      setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV
    
           ?      specifying command names containing /
    
           ?      specifying a file name containing a / as an argument  to  the  .
                  builtin command
    
           ?      Specifying  a  filename containing a slash as an argument to the
                  -p option to the hash builtin command
    
           ?      importing function definitions from  the  shell  environment  at
                  startup
    
           ?      parsing  the  value  of  SHELLOPTS from the shell environment at
                  startup
    
           ?      redirecting output using the >, >|, <>, >&, &>, and >>  redirec-
                  tion operators
    
    
           When a command that is found to be a shell script is executed (see COM-
           MAND  EXECUTION  above),  rbash turns off any restrictions in the shell
           spawned to execute the script.
    
    
    

    SEE ALSO

           Bash Reference Manual, Brian Fox and Chet Ramey
           The Gnu Readline Library, Brian Fox and Chet Ramey
           The Gnu History Library, Brian Fox and Chet Ramey
           Portable Operating System Interface (POSIX) Part 2:  Shell  and  Utili-
           ties, IEEE
           sh(1), ksh(1), csh(1)
           emacs(1), vi(1)
           readline(3)
    
    
    

    FILES

           /bin/bash
                  The bash executable
           /etc/profile
                  The systemwide initialization file, executed for login shells
           /etc/bash.bash_logout
                  The systemwide login shell cleanup file, executed when  a  login
                  shell exits
           ~/.bash_profile
                  The personal initialization file, executed for login shells
           ~/.bashrc
                  The individual per-interactive-shell startup file
           ~/.bash_logout
                  The  individual  login shell cleanup file, executed when a login
                  shell exits
           ~/.inputrc
                  Individual readline initialization file
    
    
    

    AUTHORS

           Brian Fox, Free Software Foundation
           bfox@gnu.org
    
           Chet Ramey, Case Western Reserve University
           chet.ramey@case.edu
    
    
    

    BUG REPORTS

           If you find a bug in bash, you should report it.  But first, you should
           make  sure  that  it really is a bug, and that it appears in the latest
           version  of  bash.   The  latest  version  is  always  available   from
           ftp://ftp.gnu.org/pub/bash/.
    
           Once  you  have  determined that a bug actually exists, use the bashbug
           command (from the source package) to submit a bug report.  If you  have
           a  fix,  you  are  encouraged  to  mail  that as well!  Suggestions and
           'philosophical' bug reports may be mailed to bug-bash@gnu.org or posted
           to the Usenet newsgroup gnu.bash.bug.
    
           There are some subtle differences between bash and traditional versions
           of sh, mostly because of the POSIX specification.
    
           Aliases are confusing in some uses.
    
           Shell builtin commands and functions are not stoppable/restartable.
    
           Compound commands and command sequences of the form 'a ; b ; c' are not
           handled gracefully when process suspension is attempted.  When  a  pro-
           cess is stopped, the shell immediately executes the next command in the
           sequence.  It suffices to place the sequence of commands between paren-
           theses to force it into a subshell, which may be stopped as a unit.
    
           Array variables may not (yet) be exported.
    
           There may be only one active coprocess at a time.
    
    
    

    GNU Bash-4.1 2009 December 29 BASH(1)

    
    
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