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            [+o option_name] [command_file [argument ...]]
         sh -c [-aCefnuvxIimqVEb] [+aCefnuvxIimqVEb] [-o option_name]
            [+o option_name] command_string [command_name [argument ...]]
         sh -s [-aCefnuvxIimqVEb] [+aCefnuvxIimqVEb] [-o option_name]
            [+o option_name] [argument ...]


         sh is the standard command interpreter for the system.  The current ver-
         sion of sh is in the process of being changed to conform with the POSIX
         1003.2 and 1003.2a specifications for the shell.  This version has many
         features which make it appear similar in some respects to the Korn shell,
         but it is not a Korn shell clone (see ksh(1)).  Only features designated
         by POSIX, plus a few Berkeley extensions, are being incorporated into
         this shell.  We expect POSIX conformance by the time 4.4 BSD is released.
         This man page is not intended to be a tutorial or a complete specifica-
         tion of the shell.
         The shell is a command that reads lines from either a file or the termi-
         nal, interprets them, and generally executes other commands.  It is the
         program that is running when a user logs into the system (although a user
         can select a different shell with the chsh(1) command).  The shell imple-
         ments a language that has flow control constructs, a macro facility that
         provides a variety of features in addition to data storage, along with
         built in history and line editing capabilities.  It incorporates many
         features to aid interactive use and has the advantage that the interpre-
         tative language is common to both interactive and non-interactive use
         (shell scripts).  That is, commands can be typed directly to the running
         shell or can be put into a file and the file can be executed directly by
         the shell.
         If no args are present and if the standard input of the shell is con-
         nected to a terminal (or if the -i flag is set), and the -c option is not
         present, the shell is considered an interactive shell.  An interactive
         shell generally prompts before each command and handles programming and
         command errors differently (as described below).  When first starting,
         the shell inspects argument 0, and if it begins with a dash '-', the
         shell is also considered a login shell.  This is normally done automati-
         cally by the system when the user first logs in.  A login shell first
         reads commands from the files /etc/profile and .profile if they exist.
         If the environment variable ENV is set on entry to an interactive shell,
         or is set in the .profile of a login shell, the shell next reads commands
         from the file named in ENV.  Therefore, a user should place commands that
         are to be executed only at login time in the .profile file, and commands
         that are executed for every interactive shell inside the ENV file.  To
         set the ENV variable to some file, place the following line in your
         .profile of your home directory
               ENV=$HOME/.shinit; export ENV
         substituting for ".shinit" any filename you wish.
               -a allexport     Export all variables assigned to.
               -c               Read commands from the command_string operand
                                instead of from the standard input.  Special
                                parameter 0 will be set from the command_name
                                operand and the positional parameters ($1, $2,
                                etc.)  set from the remaining argument operands.
               -C noclobber     Don't overwrite existing files with ">".
               -e errexit       If not interactive, exit immediately if any
                                untested command fails.  The exit status of a com-
                                mand is considered to be explicitly tested if the
                                command is used to control an if, elif, while, or
                                until; or if the command is the left hand operand
                                of an "&&" or "||" operator.
               -f noglob        Disable pathname expansion.
               -n noexec        If not interactive, read commands but do not exe-
                                cute them.  This is useful for checking the syntax
                                of shell scripts.
               -u nounset       Write a message to standard error when attempting
                                to expand a variable that is not set, and if the
                                shell is not interactive, exit immediately.
               -v verbose       The shell writes its input to standard error as it
                                is read.  Useful for debugging.
               -x xtrace        Write each command to standard error (preceded by
                                a '+ ') before it is executed.  Useful for debug-
               -I ignoreeof     Ignore EOF's from input when interactive.
               -i interactive   Force the shell to behave interactively.
               -l               Make dash act as if it had been invoked as a login
               -m monitor       Turn on job control (set automatically when inter-
               -s stdin         Read commands from standard input (set automati-
                                cally if no file arguments are present).  This
                                option has no effect when set after the shell has
                                already started running (i.e. with set).
               -V vi            Enable the built-in vi(1) command line editor
                                (disables -E if it has been set).
               Control operators:
                     & && ( ) ; ;; | || <newline>
               Redirection operators:
                     < > >| << >> <& >& <<- <>
         Quoting is used to remove the special meaning of certain characters or
         words to the shell, such as operators, whitespace, or keywords.  There
         are three types of quoting: matched single quotes, matched double quotes,
         and backslash.
         A backslash preserves the literal meaning of the following character,
         with the exception of <newline>.  A backslash preceding a <newline> is
         treated as a line continuation.
       Single Quotes
         Enclosing characters in single quotes preserves the literal meaning of
         all the characters (except single quotes, making it impossible to put
         single-quotes in a single-quoted string).
       Double Quotes
         Enclosing characters within double quotes preserves the literal meaning
         of all characters except dollarsign ($), backquote ('), and backslash
         (\).  The backslash inside double quotes is historically weird, and
         serves to quote only the following characters:
               $ ' " \ <newline>.
         Otherwise it remains literal.
       Reserved Words
         Reserved words are words that have special meaning to the shell and are
         recognized at the beginning of a line and after a control operator.  The
         following are reserved words:
               !       elif    fi      while   case
               else    for     then    {       }
               do      done    until   if      esac
         Their meaning is discussed later.
         An alias is a name and corresponding value set using the alias(1) builtin
         command.  Whenever a reserved word may occur (see above), and after
         checking for reserved words, the shell checks the word to see if it
         matches an alias.  If it does, it replaces it in the input stream with
         its value.  For example, if there is an alias called "lf" with the value
         "ls -F", then the input:
               lf foobar <return>
         would become
         Otherwise, a complex command or some other special construct may have
         been recognized.
       Simple Commands
         If a simple command has been recognized, the shell performs the following
               1.   Leading words of the form "name=value" are stripped off and
                    assigned to the environment of the simple command.  Redirec-
                    tion operators and their arguments (as described below) are
                    stripped off and saved for processing.
               2.   The remaining words are expanded as described in the section
                    called "Expansions", and the first remaining word is consid-
                    ered the command name and the command is located.  The remain-
                    ing words are considered the arguments of the command.  If no
                    command name resulted, then the "name=value" variable assign-
                    ments recognized in item 1 affect the current shell.
               3.   Redirections are performed as described in the next section.
         Redirections are used to change where a command reads its input or sends
         its output.  In general, redirections open, close, or duplicate an exist-
         ing reference to a file.  The overall format used for redirection is:
               [n] redir-op file
         where redir-op is one of the redirection operators mentioned previously.
         Following is a list of the possible redirections.  The [n] is an optional
         number, as in '3' (not '[3]'), that refers to a file descriptor.
               [n]> file   Redirect standard output (or n) to file.
               [n]>| file  Same, but override the -C option.
               [n]>> file  Append standard output (or n) to file.
               [n]< file   Redirect standard input (or n) from file.
               [n1]<&n2    Duplicate standard input (or n1) from file descriptor
               [n]<&-      Close standard input (or n).
               [n1]>&n2    Duplicate standard output (or n1) to n2.
               [n]>&-      Close standard output (or n).
               [n]<> file  Open file for reading and writing on standard input (or
       Search and Execution
         There are three types of commands: shell functions, builtin commands, and
         normal programs -- and the command is searched for (by name) in that
         order.  They each are executed in a different way.
         When a shell function is executed, all of the shell positional parameters
         (except $0, which remains unchanged) are set to the arguments of the
         shell function.  The variables which are explicitly placed in the envi-
         ronment of the command (by placing assignments to them before the func-
         tion name) are made local to the function and are set to the values
         given.  Then the command given in the function definition is executed.
         The positional parameters are restored to their original values when the
         command completes.  This all occurs within the current shell.
         Shell builtins are executed internally to the shell, without spawning a
         new process.
         Otherwise, if the command name doesn't match a function or builtin, the
         command is searched for as a normal program in the file system (as
         described in the next section).  When a normal program is executed, the
         shell runs the program, passing the arguments and the environment to the
         program.  If the program is not a normal executable file (i.e., if it
         does not begin with the "magic number" whose ASCII representation is
         "#!", so execve(2) returns ENOEXEC then) the shell will interpret the
         program in a subshell.  The child shell will reinitialize itself in this
         case, so that the effect will be as if a new shell had been invoked to
         handle the ad-hoc shell script, except that the location of hashed com-
         mands located in the parent shell will be remembered by the child.
         Note that previous versions of this document and the source code itself
         misleadingly and sporadically refer to a shell script without a magic
         number as a "shell procedure".
       Path Search
         When locating a command, the shell first looks to see if it has a shell
         function by that name.  Then it looks for a builtin command by that name.
         If a builtin command is not found, one of two things happen:
         1.   Command names containing a slash are simply executed without per-
              forming any searches.
         2.   The shell searches each entry in PATH in turn for the command.  The
              value of the PATH variable should be a series of entries separated
              by colons.  Each entry consists of a directory name.  The current
              directory may be indicated implicitly by an empty directory name, or
              explicitly by a single period.
       Command Exit Status
         Each command has an exit status that can influence the behaviour of other
         shell commands.  The paradigm is that a command exits with zero for nor-
         mal or success, and non-zero for failure, error, or a false indication.
         ?   pipeline
         ?   list or compound-list
         ?   compound command
         ?   function definition
         Unless otherwise stated, the exit status of a command is that of the last
         simple command executed by the command.
         A pipeline is a sequence of one or more commands separated by the control
         operator |.  The standard output of all but the last command is connected
         to the standard input of the next command.  The standard output of the
         last command is inherited from the shell, as usual.
         The format for a pipeline is:
               [!] command1 [| command2 ...]
         The standard output of command1 is connected to the standard input of
         command2.  The standard input, standard output, or both of a command is
         considered to be assigned by the pipeline before any redirection speci-
         fied by redirection operators that are part of the command.
         If the pipeline is not in the background (discussed later), the shell
         waits for all commands to complete.
         If the reserved word ! does not precede the pipeline, the exit status is
         the exit status of the last command specified in the pipeline.  Other-
         wise, the exit status is the logical NOT of the exit status of the last
         command.  That is, if the last command returns zero, the exit status is
         1; if the last command returns greater than zero, the exit status is
         Because pipeline assignment of standard input or standard output or both
         takes place before redirection, it can be modified by redirection.  For
               $ command1 2>&1 | command2
         sends both the standard output and standard error of command1 to the
         standard input of command2.
         A ; or <newline> terminator causes the preceding AND-OR-list (described
         next) to be executed sequentially; a & causes asynchronous execution of
         the preceding AND-OR-list.
         Note that unlike some other shells, each process in the pipeline is a
         child of the invoking shell (unless it is a shell builtin, in which case
       Lists -- Generally Speaking
         A list is a sequence of zero or more commands separated by newlines,
         semicolons, or ampersands, and optionally terminated by one of these
         three characters.  The commands in a list are executed in the order they
         are written.  If command is followed by an ampersand, the shell starts
         the command and immediately proceed onto the next command; otherwise it
         waits for the command to terminate before proceeding to the next one.
       Short-Circuit List Operators
         "&&" and "||" are AND-OR list operators.  "&&" executes the first com-
         mand, and then executes the second command iff the exit status of the
         first command is zero.  "||" is similar, but executes the second command
         iff the exit status of the first command is nonzero.  "&&" and "||" both
         have the same priority.
       Flow-Control Constructs -- if, while, for, case
         The syntax of the if command is
               if list
               then list
               [ elif list
               then    list ] ...
               [ else list ]
         The syntax of the while command is
               while list
               do   list
         The two lists are executed repeatedly while the exit status of the first
         list is zero.  The until command is similar, but has the word until in
         place of while, which causes it to repeat until the exit status of the
         first list is zero.
         The syntax of the for command is
               for variable [ in [ word ... ] ]
               do   list
         The words following in are expanded, and then the list is executed
         repeatedly with the variable set to each word in turn.  Omitting in word
         ... is equivalent to in "$@".
         The syntax of the break and continue command is
               break [ num ]
               continue [ num ]
       Grouping Commands Together
         Commands may be grouped by writing either
               { list; }
         The first of these executes the commands in a subshell.  Builtin commands
         grouped into a (list) will not affect the current shell.  The second form
         does not fork another shell so is slightly more efficient.  Grouping com-
         mands together this way allows you to redirect their output as though
         they were one program:
               { printf " hello " ; printf " world\n" ; } > greeting
         Note that "}" must follow a control operator (here, ";") so that it is
         recognized as a reserved word and not as another command argument.
         The syntax of a function definition is
               name () command
         A function definition is an executable statement; when executed it
         installs a function named name and returns an exit status of zero.  The
         command is normally a list enclosed between "{" and "}".
         Variables may be declared to be local to a function by using a local com-
         mand.  This should appear as the first statement of a function, and the
         syntax is
               local [variable | -] ...
         Local is implemented as a builtin command.
         When a variable is made local, it inherits the initial value and exported
         and readonly flags from the variable with the same name in the surround-
         ing scope, if there is one.  Otherwise, the variable is initially unset.
         The shell uses dynamic scoping, so that if you make the variable x local
         to function f, which then calls function g, references to the variable x
         made inside g will refer to the variable x declared inside f, not to the
         global variable named x.
         The only special parameter that can be made local is "-".  Making "-"
         local any shell options that are changed via the set command inside the
         function to be restored to their original values when the function
         The syntax of the return command is
         ics, numerics, and underscores - the first of which must not be numeric.
         A parameter can also be denoted by a number or a special character as
         explained below.
       Positional Parameters
         A positional parameter is a parameter denoted by a number (n > 0).  The
         shell sets these initially to the values of its command line arguments
         that follow the name of the shell script.  The set builtin can also be
         used to set or reset them.
       Special Parameters
         A special parameter is a parameter denoted by one of the following spe-
         cial characters.  The value of the parameter is listed next to its char-
         *            Expands to the positional parameters, starting from one.
                      When the expansion occurs within a double-quoted string it
                      expands to a single field with the value of each parameter
                      separated by the first character of the IFS variable, or by
                      a <space> if IFS is unset.
         @            Expands to the positional parameters, starting from one.
                      When the expansion occurs within double-quotes, each posi-
                      tional parameter expands as a separate argument.  If there
                      are no positional parameters, the expansion of @ generates
                      zero arguments, even when @ is double-quoted.  What this
                      basically means, for example, is if $1 is "abc" and $2 is
                      "def ghi", then "$@" expands to the two arguments:
                            "abc" "def ghi"
         #            Expands to the number of positional parameters.
         ?            Expands to the exit status of the most recent pipeline.
         - (Hyphen.)  Expands to the current option flags (the single-letter
                      option names concatenated into a string) as specified on
                      invocation, by the set builtin command, or implicitly by the
         $            Expands to the process ID of the invoked shell.  A subshell
                      retains the same value of $ as its parent.
         !            Expands to the process ID of the most recent background com-
                      mand executed from the current shell.  For a pipeline, the
                      process ID is that of the last command in the pipeline.
         0 (Zero.)    Expands to the name of the shell or shell script.
       Word Expansions
         This clause describes the various expansions that are performed on words.
         Not all expansions are performed on every word, as explained later.
              the IFS variable is null.
         3.   Pathname Expansion (unless set -f is in effect).
         4.   Quote Removal.
         The $ character is used to introduce parameter expansion, command substi-
         tution, or arithmetic evaluation.
       Tilde Expansion (substituting a user's home directory)
         A word beginning with an unquoted tilde character (~) is subjected to
         tilde expansion.  All the characters up to a slash (/) or the end of the
         word are treated as a username and are replaced with the user's home
         directory.  If the username is missing (as in ~/foobar), the tilde is
         replaced with the value of the HOME variable (the current user's home
       Parameter Expansion
         The format for parameter expansion is as follows:
         where expression consists of all characters until the matching "}".  Any
         "}" escaped by a backslash or within a quoted string, and characters in
         embedded arithmetic expansions, command substitutions, and variable
         expansions, are not examined in determining the matching "}".
         The simplest form for parameter expansion is:
         The value, if any, of parameter is substituted.
         The parameter name or symbol can be enclosed in braces, which are
         optional except for positional parameters with more than one digit or
         when parameter is followed by a character that could be interpreted as
         part of the name.  If a parameter expansion occurs inside double-quotes:
         1.   Pathname expansion is not performed on the results of the expansion.
         2.   Field splitting is not performed on the results of the expansion,
              with the exception of @.
         In addition, a parameter expansion can be modified by using one of the
         following formats.
         ${parameter:-word}    Use Default Values.  If parameter is unset or null,
                               the expansion 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 parame-
                               null, null is substituted; otherwise, the expansion
                               of word is substituted.
         In the parameter expansions shown previously, use of the colon in the
         format results in a test for a parameter that is unset or null; omission
         of the colon results in a test for a parameter that is only unset.
         ${#parameter}         String Length.  The length in characters of the
                               value of parameter.
         The following four varieties of parameter expansion provide for substring
         processing.  In each case, pattern matching notation (see Shell
         Patterns), rather than regular expression notation, is used to evaluate
         the patterns.  If parameter is * or @, the result of the expansion is
         unspecified.  Enclosing the full parameter expansion string in double-
         quotes does not cause the following four varieties of pattern characters
         to be quoted, whereas quoting characters within the braces has this
         ${parameter%word}     Remove Smallest Suffix Pattern.  The word is
                               expanded to produce a pattern.  The parameter
                               expansion then results in parameter, with the
                               smallest portion of the suffix matched by the pat-
                               tern deleted.
         ${parameter%%word}    Remove Largest Suffix Pattern.  The word is
                               expanded to produce a pattern.  The parameter
                               expansion then results in parameter, with the
                               largest portion of the suffix matched by the pat-
                               tern deleted.
         ${parameter#word}     Remove Smallest Prefix Pattern.  The word is
                               expanded to produce a pattern.  The parameter
                               expansion then results in parameter, with the
                               smallest portion of the prefix matched by the pat-
                               tern deleted.
         ${parameter##word}    Remove Largest Prefix Pattern.  The word is
                               expanded to produce a pattern.  The parameter
                               expansion then results in parameter, with the
                               largest portion of the prefix matched by the pat-
                               tern deleted.
       Command Substitution
         Command substitution allows the output of a command to be substituted in
         place of the command name itself.  Command substitution occurs when the
         command is enclosed as follows:
         or ("backquoted" version):
         The expression is treated as if it were in double-quotes, except that a
         double-quote inside the expression is not treated specially.  The shell
         expands all tokens in the expression for parameter expansion, command
         substitution, and quote removal.
         Next, the shell treats this as an arithmetic expression and substitutes
         the value of the expression.
       White Space Splitting (Field Splitting)
         After parameter expansion, command substitution, and arithmetic expansion
         the shell scans the results of expansions and substitutions that did not
         occur in double-quotes for field splitting and multiple fields can
         The shell treats each character of the IFS as a delimiter and uses the
         delimiters to split the results of parameter expansion and command sub-
         stitution into fields.
       Pathname Expansion (File Name Generation)
         Unless the -f flag is set, file name generation is performed after word
         splitting is complete.  Each word is viewed as a series of patterns, sep-
         arated by slashes.  The process of expansion replaces the word with the
         names of all existing files whose names can be formed by replacing each
         pattern with a string that matches the specified pattern.  There are two
         restrictions on this: first, a pattern cannot match a string containing a
         slash, and second, a pattern cannot match a string starting with a period
         unless the first character of the pattern is a period.  The next section
         describes the patterns used for both Pathname Expansion and the case com-
       Shell Patterns
         A pattern consists of normal characters, which match themselves, and
         meta-characters.  The meta-characters are "!", "*", "?", and "[".  These
         characters lose their special meanings if they are quoted.  When command
         or variable substitution is performed and the dollar sign or back quotes
         are not double quoted, the value of the variable or the output of the
         command is scanned for these characters and they are turned into meta-
         An asterisk ("*") matches any string of characters.  A question mark
         matches any single character.  A left bracket ("[") introduces a charac-
         ter class.  The end of the character class is indicated by a ("]"); if
         the "]" is missing then the "[" matches a "[" rather than introducing a
         character class.  A character class matches any of the characters between
         the square brackets.  A range of characters may be specified using a
         minus sign.  The character class may be complemented by making an excla-
         mation point the first character of the character class.
         To include a "]" in a character class, make it the first character listed
                The commands in the specified file are read and executed by the
         alias [name[=string ...]]
                If name=string is specified, the shell defines the alias name with
                value string.  If just name is specified, the value of the alias
                name is printed.  With no arguments, the alias builtin prints the
                names and values of all defined aliases (see unalias).
         bg [job] ...
                Continue the specified jobs (or the current job if no jobs are
                given) in the background.
         command [-p] [-v] [-V] command [arg ...]
                Execute the specified command but ignore shell functions when
                searching for it.  (This is useful when you have a shell function
                with the same name as a builtin command.)
                -p     search for command using a PATH that guarantees to find all
                       the standard utilities.
                -V     Do not execute the command but search for the command and
                       print the resolution of the command search.  This is the
                       same as the type builtin.
                -v     Do not execute the command but search for the command and
                       print the absolute pathname of utilities, the name for
                       builtins or the expansion of aliases.
         cd -
         cd [-LP] [directory]
                Switch to the specified directory (default HOME).  If an entry for
                CDPATH appears in the environment of the cd command or the shell
                variable CDPATH is set and the directory name does not begin with
                a slash, then the directories listed in CDPATH will be searched
                for the specified directory.  The format of CDPATH is the same as
                that of PATH.  If a single dash is specified as the argument, it
                will be replaced by the value of OLDPWD.  The cd command will
                print out the name of the directory that it actually switched to
                if this is different from the name that the user gave.  These may
                be different either because the CDPATH mechanism was used or
                because the argument is a single dash.  The -P option causes the
                physical directory structure to be used, that is, all symbolic
                links are resolved to their respective values.  The -L option
                turns off the effect of any preceding -P options.
         echo [-n] args...
                Print the arguments on the standard output, separated by spaces.
                Unless the -n option is present, a newline is output following the
                \r      Output a carriage return.
                \t      Output a (horizontal) tab character.
                \v      Output a vertical tab.
                        Output the character whose value is given by zero to three
                        octal digits.  If there are zero digits, a nul character
                        is output.
                \\      Output a backslash.
                All other backslash sequences elicit undefined behaviour.
         eval string ...
                Concatenate all the arguments with spaces.  Then re-parse and exe-
                cute the command.
         exec [command arg ...]
                Unless command is omitted, the shell process is replaced with the
                specified program (which must be a real program, not a shell
                builtin or function).  Any redirections on the exec command are
                marked as permanent, so that they are not undone when the exec
                command finishes.
         exit [exitstatus]
                Terminate the shell process.  If exitstatus is given it is used as
                the exit status of the shell; otherwise the exit status of the
                preceding command is used.
         export name ...
         export -p
                The specified names are exported so that they will appear in the
                environment of subsequent commands.  The only way to un-export a
                variable is to unset it.  The shell allows the value of a variable
                to be set at the same time it is exported by writing
                      export name=value
                With no arguments the export command lists the names of all
                exported variables.  With the -p option specified the output will
                be formatted suitably for non-interactive use.
         fc [-e editor] [first [last]]
         fc -l [-nr] [first [last]]
         fc -s [old=new] [first]
                The fc builtin lists, or edits and re-executes, commands previ-
                ously entered to an interactive shell.
                -n     Suppress command numbers when listing with -l.
                -r     Reverse the order of the commands listed (with -l) or
                       edited (with neither -l nor -s).
                -s     Re-execute the command without invoking an editor.
                last   Select the commands to list or edit.  The number of previ-
                       ous commands that can be accessed are determined by the
                       value of the HISTSIZE variable.  The value of first or last
                       or both are one of the following:
                              A positive number representing a command number;
                              command numbers can be displayed with the -l option.
                              A negative decimal number representing the command
                              that was executed number of commands previously.
                              For example, -1 is the immediately previous command.
                       A string indicating the most recently entered command that
                       begins with that string.  If the old=new operand is not
                       also specified with -s, the string form of the first
                       operand cannot contain an embedded equal sign.
                The following environment variables affect the execution of fc:
                FCEDIT    Name of the editor to use.
                HISTSIZE  The number of previous commands that are accessible.
         fg [job]
                Move the specified job or the current job to the foreground.
         getopts optstring var
                The POSIX getopts command, not to be confused with the Bell Labs
                -derived getopt(1).
                The first argument should be a series of letters, each of which
                may be optionally followed by a colon to indicate that the option
                requires an argument.  The variable specified is set to the parsed
                The getopts command deprecates the older getopt(1) utility due to
                its handling of arguments containing whitespace.
                The getopts builtin may be used to obtain options and their argu-
                ing a colon as the first character of optstring all errors will be
                A nonzero value is returned when the last option is reached.  If
                there are no remaining arguments, getopts will set var to the spe-
                cial option, "--", otherwise, it will set var to "?".
                The following code fragment shows how one might process the argu-
                ments for a command that can take the options [a] and [b], and the
                option [c], which requires an argument.
                      while getopts abc: f
                              case $f in
                              a | b)  flag=$f;;
                              c)      carg=$OPTARG;;
                              \?)     echo $USAGE; exit 1;;
                      shift 'expr $OPTIND - 1'
                This code will accept any of the following as equivalent:
                      cmd -acarg file file
                      cmd -a -c arg file file
                      cmd -carg -a file file
                      cmd -a -carg -- file file
         hash -rv command ...
                The shell maintains a hash table which remembers the locations of
                commands.  With no arguments whatsoever, the hash command prints
                out the contents of this table.  Entries which have not been
                looked at since the last cd command are marked with an asterisk;
                it is possible for these entries to be invalid.
                With arguments, the hash command removes the specified commands
                from the hash table (unless they are functions) and then locates
                them.  With the -v option, hash prints the locations of the com-
                mands as it finds them.  The -r option causes the hash command to
                delete all the entries in the hash table except for functions.
         pwd [-LP]
                builtin command remembers what the current directory is rather
                than recomputing it each time.  This makes it faster.  However, if
                the current directory is renamed, the builtin version of pwd will
                continue to print the old name for the directory.  The -P option
                causes the physical value of the current working directory to be
                shown, that is, all symbolic links are resolved to their respec-
                tive values.  The -L option turns off the effect of any preceding
                -P options.
         read [-p prompt] [-r] variable [...]
                treated literally.  If a backslash is followed by a newline, the
                backslash and the newline will be deleted.
         readonly name ...
         readonly -p
                The specified names are marked as read only, so that they cannot
                be subsequently modified or unset.  The shell allows the value of
                a variable to be set at the same time it is marked read only by
                      readonly name=value
                With no arguments the readonly command lists the names of all read
                only variables.  With the -p option specified the output will be
                formatted suitably for non-interactive use.
         printf format [arguments ...]
                printf formats and prints its arguments, after the first, under
                control of the format.  The format is a character string which
                contains three types of objects: plain characters, which are sim-
                ply copied to standard output, character escape sequences which
                are converted and copied to the standard output, and format speci-
                fications, each of which causes printing of the next successive
                The arguments after the first are treated as strings if the corre-
                sponding format is either b, c or s; otherwise it is evaluated as
                a C constant, with the following extensions:
                      ?   A leading plus or minus sign is allowed.
                      ?   If the leading character is a single or double quote,
                          the value is the ASCII code of the next character.
                The format string is reused as often as necessary to satisfy the
                arguments.  Any extra format specifications are evaluated with
                zero or the null string.
                Character escape sequences are in backslash notation as defined in
                ANSI X3.159-1989 ("ANSI C").  The characters and their meanings
                are as follows:
                      \a      Write a <bell> character.
                      \b      Write a <backspace> character.
                      \f      Write a <form-feed> character.
                      \n      Write a <new-line> character.
                      \r      Write a <carriage return> character.
                        #       A '#' character specifying that the value should
                                be printed in an ''alternative form''.  For b, c,
                                d, and s formats, this option has no effect.  For
                                the o format the precision of the number is
                                increased to force the first character of the out-
                                put string to a zero.  For the x (X) format, a
                                non-zero result has the string 0x (0X) prepended
                                to it.  For e, E, f, g, and G formats, the result
                                will always contain a decimal point, even if no
                                digits follow the point (normally, a decimal point
                                only appears in the results of those formats if a
                                digit follows the decimal point).  For g and G
                                formats, trailing zeros are not removed from the
                                result as they would otherwise be.
                        -       A minus sign '-' which specifies left adjustment
                                of the output in the indicated field;
                        +       A '+' character specifying that there should
                                always be a sign placed before the number when
                                using signed formats.
                        ' '     A space specifying that a blank should be left
                                before a positive number for a signed format.  A
                                '+' overrides a space if both are used;
                        0       A zero '0' character indicating that zero-padding
                                should be used rather than blank-padding.  A '-'
                                overrides a '0' if both are used;
                Field Width:
                        An optional digit string specifying a field width; if the
                        output string has fewer characters than the field width it
                        will be blank-padded on the left (or right, if the left-
                        adjustment indicator has been given) to make up the field
                        width (note that a leading zero is a flag, but an embedded
                        zero is part of a field width);
                        An optional period, '.', followed by an optional digit
                        string giving a precision which specifies the number of
                        digits to appear after the decimal point, for e and f for-
                        mats, or the maximum number of characters to be printed
                        from a string (b and s formats); if the digit string is
                        missing, the precision is treated as zero;
                        A character which indicates the type of format to use (one
                        of diouxXfwEgGbcs).
                A field width or precision may be '*' instead of a digit string.
                eE          The argument is printed in the style [-]d.ddde?dd
                            where there is one digit before the decimal point and
                            the number after is equal to the precision specifica-
                            tion for the argument; when the precision is missing,
                            6 digits are produced.  An upper-case E is used for an
                            'E' format.
                gG          The argument is printed in style f or in style e (E)
                            whichever gives full precision in minimum space.
                b           Characters from the string argument are printed with
                            backslash-escape sequences expanded.
                            The following additional backslash-escape sequences
                            are supported:
                            \c      Causes sh to ignore any remaining characters
                                    in the string operand containing it, any
                                    remaining string operands, and any additional
                                    characters in the format operand.
                            \0num   Write an 8-bit character whose ASCII value is
                                    the 1-, 2-, or 3-digit octal number num.
                c           The first character of argument is printed.
                s           Characters from the string argument are printed until
                            the end is reached or until the number of characters
                            indicated by the precision specification is reached;
                            if the precision is omitted, all characters in the
                            string are printed.
                %           Print a '%'; no argument is used.
                In no case does a non-existent or small field width cause trunca-
                tion of a field; padding takes place only if the specified field
                width exceeds the actual width.
         set [{ -options | +options | -- }] arg ...
                The set command performs three different functions.
                With no arguments, it lists the values of all shell variables.
                If options are given, it sets the specified option flags, or
                clears them as described in the section called Argument List
                Processing.  As a special case, if the option is -o or +o and no
                argument is supplied, the shell prints the settings of all its
                options.  If the option is -o, the settings are printed in a
                human-readable format; if the option is +o, the settings are
                printed in a format suitable for reinput to the shell to affect
                the same option settings.
         test expression
         [ expression ]
                The test utility evaluates the expression and, if it evaluates to
                true, returns a zero (true) exit status; otherwise it returns 1
                (false).  If there is no expression, test also returns 1 (false).
                All operators and flags are separate arguments to the test util-
                The following primaries are used to construct expression:
                -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 (regardless of type).
                -f file       True if file exists and is a regular file.
                -g file       True if file exists and its set group ID flag is
                -h file       True if file exists and is a symbolic link.
                -k file       True if file exists and its sticky bit is set.
                -n string     True if the length of string is nonzero.
                -p file       True if file 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
                -t file_descriptor
                              True if the file whose file descriptor number is
                              file_descriptor is open and is associated with a
                -u file       True if file exists and its set user ID flag is set.
                -w file       True if file exists and is writable.  True indicates
                              only that the write flag is on.  The file is not
                              writable on a read-only file system even if this
                              test indicates true.
                -x file       True if file exists and is executable.  True indi-
                              cates only that the execute flag is on.  If file is
                              tive group id of this process.
                -S file       True if file exists and is a socket.
                file1 -nt file2
                              True if file1 and file2 exist and file1 is newer
                              than file2.
                file1 -ot file2
                              True if file1 and file2 exist and file1 is older
                              than file2.
                file1 -ef file2
                              True if file1 and file2 exist and refer to the same
                string        True if string is not the null string.
                s1 = s2       True if the strings s1 and s2 are identical.
                s1 != s2      True if the strings s1 and s2 are not identical.
                s1 < s2       True if string s1 comes before s2 based on the ASCII
                              value of their characters.
                s1 > s2       True if string s1 comes after s2 based on the ASCII
                              value of their characters.
                n1 -eq n2     True if the integers n1 and n2 are algebraically
                n1 -ne n2     True if the integers n1 and n2 are not algebraically
                n1 -gt n2     True if the integer n1 is algebraically greater than
                              the integer n2.
                n1 -ge n2     True if the integer n1 is algebraically greater than
                              or equal to the integer n2.
                n1 -lt n2     True if the integer n1 is algebraically less than
                              the integer n2.
                n1 -le n2     True if the integer n1 is algebraically less than or
                              equal to the integer n2.
                These primaries can be combined with the following operators:
                ! expression  True if expression is false.
                expression1 -a expression2
                              True if both expression1 and expression2 are true.
                number or as the name of the signal.  If signal is 0, the action
                is executed when the shell exits.  action may be null, which cause
                the specified signals to be ignored.  With action omitted or set
                to '-' the specified signals are set to their default action.
                When the shell forks off a subshell, it resets trapped (but not
                ignored) signals to the default action.  The trap command has no
                effect on signals that were ignored on entry to the shell.  trap
                without any arguments cause it to write a list of signals and
                their associated action to the standard output in a format that is
                suitable as an input to the shell that achieves the same trapping
                List trapped signals and their corresponding action
                      trap '' INT QUIT tstp 30
                Ignore signals INT QUIT TSTP USR1
                      trap date INT
                Print date upon receiving signal INT
         type [name ...]
                Interpret each name as a command and print the resolution of the
                command search.  Possible resolutions are: shell keyword, alias,
                shell builtin, command, tracked alias and not found.  For aliases
                the alias expansion is printed; for commands and tracked aliases
                the complete pathname of the command is printed.
         ulimit [-H | -S] [-a | -tfdscmlpn [value]]
                Inquire about or set the hard or soft limits on processes or set
                new limits.  The choice between hard limit (which no process is
                allowed to violate, and which may not be raised once it has been
                lowered) and soft limit (which causes processes to be signaled but
                not necessarily killed, and which may be raised) is made with
                these flags:
                -H          set or inquire about hard limits
                -S          set or inquire about soft limits.  If neither -H nor
                            -S is specified, the soft limit is displayed or both
                            limits are set.  If both are specified, the last one
                The limit to be interrogated or set, then, is chosen by specifying
                any one of these flags:
                -a          show all the current limits
                -m          show or set the limit on the total physical memory
                            that can be in use by a process (in kilobytes)
                -l          show or set the limit on how much memory a process can
                            lock with mlock(2) (in kilobytes)
                -p          show or set the limit on the number of processes this
                            user can have at one time
                -n          show or set the limit on the number files a process
                            can have open at once
                If none of these is specified, it is the limit on file size that
                is shown or set.  If value is specified, the limit is set to that
                number; otherwise the current limit is displayed.
                Limits of an arbitrary process can be displayed or set using the
                sysctl(8) utility.
         umask [mask]
                Set the value of umask (see umask(2)) to the specified octal
                value.  If the argument is omitted, the umask value is printed.
         unalias [-a] [name]
                If name is specified, the shell removes that alias.  If -a is
                specified, all aliases are removed.
         unset [-fv] name ...
                The specified variables and functions are unset and unexported.
                If -f or -v is specified, the corresponding function or variable
                is unset, respectively.  If a given name corresponds to both a
                variable and a function, and no options are given, only the vari-
                able is unset.
         wait [job]
                Wait for the specified job to complete and return the exit status
                of the last process in the job.  If the argument is omitted, wait
                for all jobs to complete and the return an exit status of zero.
       Command Line Editing
         When sh is being used interactively from a terminal, the current command
         and the command history (see fc in Builtins) can be edited using vi-mode
         command-line editing.  This mode uses commands, described below, similar
         to a subset of those described in the vi man page.  The command 'set -o
         vi' enables vi-mode editing and place sh into vi insert mode.  With vi-
         mode enabled, sh can be switched between insert mode and command mode.
         The editor is not described in full here, but will be in a later docu-
         ment.  It's similar to vi: typing <ESC> will throw you into command VI
         command mode.  Hitting <return> while in command mode will pass the line
         to the shell.
                    tion Path Search.
         CDPATH     The search path used with the cd builtin.
         MAIL       The name of a mail file, that will be checked for the arrival
                    of new mail.  Overridden by MAILPATH.
         MAILCHECK  The frequency in seconds that the shell checks for the arrival
                    of mail in the files specified by the MAILPATH or the MAIL
                    file.  If set to 0, the check will occur at each prompt.
         MAILPATH   A colon ":" separated list of file names, for the shell to
                    check for incoming mail.  This environment setting overrides
                    the MAIL setting.  There is a maximum of 10 mailboxes that can
                    be monitored at once.
         PS1        The primary prompt string, which defaults to "$  ", unless you
                    are the superuser, in which case it defaults to "#  ".
         PS2        The secondary prompt string, which defaults to ">  ".
         PS4        Output before each line when execution trace (set -x) is
                    enabled, defaults to "+  ".
         IFS        Input Field Separators.  This is normally set to <space>,
                    <tab>, and <newline>.  See the White Space Splitting section
                    for more details.
         TERM       The default terminal setting for the shell.  This is inherited
                    by children of the shell, and is used in the history editing
         HISTSIZE   The number of lines in the history buffer for the shell.
         PWD        The logical value of the current working directory.  This is
                    set by the cd command.
         OLDPWD     The previous logical value of the current working directory.
                    This is set by the cd command.
         PPID       The process ID of the parent process of the shell.




         csh(1), echo(1), getopt(1), ksh(1), login(1), printf(1), test(1),
         getopt(3), passwd(5), environ(7), sysctl(8)



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