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           expect [ -dDinN ] [ -c cmds ] [ [ -[f|b] ] cmdfile ] [ args ]


           Expect  is a program that "talks" to other interactive programs accord-
           ing to a script.  Following  the  script,  Expect  knows  what  can  be
           expected  from  a  program and what the correct response should be.  An
           interpreted language provides branching and high-level  control  struc-
           tures  to  direct the dialogue.  In addition, the user can take control
           and interact directly when desired, afterward returning control to  the
           Expectk is a mixture of Expect and Tk.  It behaves just like Expect and
           Tk's wish.  Expect can also be used directly in  C  or  C++  (that  is,
           without Tcl).  See libexpect(3).
           The name "Expect" comes from the idea of send/expect sequences popular-
           ized by uucp, kermit and other modem control programs.  However  unlike
           uucp,  Expect is generalized so that it can be run as a user-level com-
           mand with any program and task in mind.  Expect can  actually  talk  to
           several programs at the same time.
           For example, here are some things Expect can do:
                  ?   Cause  your computer to dial you back, so that you can login
                      without paying for the call.
                  ?   Start a game (e.g., rogue) and if the optimal  configuration
                      doesn't  appear, restart it (again and again) until it does,
                      then hand over control to you.
                  ?   Run fsck, and in response to its  questions,  answer  "yes",
                      "no"  or  give  control  back to you, based on predetermined
                  ?   Connect to another network or  BBS  (e.g.,  MCI  Mail,  Com-
                      puServe)  and  automatically  retrieve  your mail so that it
                      appears as if it was originally sent to your local system.
                  ?   Carry environment variables, current directory, or any  kind
                      of information across rlogin, telnet, tip, su, chgrp, etc.
           There  are  a  variety  of  reasons  why the shell cannot perform these
           tasks.  (Try, you'll see.)  All are possible with Expect.
           In general, Expect is useful for running  any  program  which  requires
           interaction between the program and the user.  All that is necessary is
           that the interaction can be characterized programmatically.  Expect can
           also give the user back control (without halting the program being con-
           trolled) if desired.  Similarly, the user can  return  control  to  the
           script at any time.
           cuted with a single -c by separating them  with  semicolons.   Commands
           are  executed  in  the  order  they  appear.  (When using Expectk, this
           option is specified as -command.)
           The -d flag enables some diagnostic  output,  which  primarily  reports
           internal  activity  of commands such as expect and interact.  This flag
           has the same effect as "exp_internal 1" at the beginning of  an  Expect
           script,  plus the version of Expect is printed.  (The strace command is
           useful for tracing statements, and the  trace  command  is  useful  for
           tracing  variable  assignments.)   (When  using Expectk, this option is
           specified as -diag.)
           The -D flag enables an interactive debugger.  An integer  value  should
           follow.   The  debugger will take control before the next Tcl procedure
           if the value is non-zero or if a ^C is pressed (or a breakpoint is hit,
           or  other appropriate debugger command appears in the script).  See the
           README file or SEE ALSO (below) for more information on  the  debugger.
           (When using Expectk, this option is specified as -Debug.)
           The -f flag prefaces a file from which to read commands from.  The flag
           itself is optional as it is only useful when using the #! notation (see
           above),  so  that  other arguments may be supplied on the command line.
           (When using Expectk, this option is specified as -file.)
           By default, the command file is read into memory and  executed  in  its
           entirety.   It  is  occasionally  desirable to read files one line at a
           time.  For example, stdin is read this way.  In order  to  force  arbi-
           trary  files  to  be  handled  this  way, use the -b flag.  (When using
           Expectk, this option is specified as -buffer.)  Note that stdio-buffer-
           ing  may  still  take  place however this shouldn't cause problems when
           reading from a fifo or stdin.
           If the string "-" is supplied as a filename,  standard  input  is  read
           instead.  (Use "./-" to read from a file actually named "-".)
           The  -i flag causes Expect to interactively prompt for commands instead
           of reading them from a file.  Prompting is terminated via the exit com-
           mand or upon EOF.  See interpreter (below) for more information.  -i is
           assumed if neither a command file nor -c is used.  (When using Expectk,
           this option is specified as -interactive.)
           --  may  be  used to delimit the end of the options.  This is useful if
           you want to pass an option-like argument  to  your  script  without  it
           being  interpreted  by  Expect.   This can usefully be placed in the #!
           line to prevent any flag-like interpretation by Expect.   For  example,
           the  following  will leave the original arguments (including the script
           name) in the variable argv.
               #!/usr/local/bin/expect --
           Note that  the  usual  getopt(3)  and  execve(2)  conventions  must  be
           observed when adding arguments to the #! line.
           argv0  is  defined to be the name of the script (or binary if no script
           is used).  For example, the following prints out the name of the script
           and the first three arguments:
               send_user "$argv0 [lrange $argv 0 2]\n"


           Expect  uses  Tcl  (Tool  Command Language).  Tcl provides control flow
           (e.g., if, for, break), expression evaluation and  several  other  fea-
           tures such as recursion, procedure definition, etc.  Commands used here
           but not defined (e.g., set, if, exec) are Tcl  commands  (see  tcl(3)).
           Expect supports additional commands, described below.  Unless otherwise
           specified, commands return the empty string.
           Commands are listed alphabetically so that they can be quickly located.
           However,  new users may find it easier to start by reading the descrip-
           tions of spawn, send, expect, and interact, in that order.
           Note that the best introduction to the language (both Expect  and  Tcl)
           is provided in the book "Exploring Expect" (see SEE ALSO below).  Exam-
           ples are included in this man page but they are very limited since this
           man page is meant primarily as reference material.
           Note  that in the text of this man page, "Expect" with an uppercase "E"
           refers to the Expect program  while  "expect"  with  a  lower-case  "e"
           refers to the expect command within the Expect program.)
           close [-slave] [-onexec 0|1] [-i spawn_id]
                 closes  the  connection to the current process.  Most interactive
                 programs will detect EOF on their stdin and exit; thus close usu-
                 ally  suffices to kill the process as well.  The -i flag declares
                 the process to close corresponding to the named spawn_id.
                 Both expect and interact will detect  when  the  current  process
                 exits and implicitly do a close.  But if you kill the process by,
                 say, "exec kill $pid", you will need to explicitly call close.
                 The -onexec flag determines whether the spawn id will  be  closed
                 in  any new spawned processes or if the process is overlayed.  To
                 leave a spawn id open, use the value 0.  A non-zero integer value
                 will force the spawn closed (the default) in any new processes.
                 The  -slave  flag  closes the slave associated with the spawn id.
                 (See "spawn -pty".)  When the connection is closed, the slave  is
                 automatically closed as well if still open.
                 No  matter whether the connection is closed implicitly or explic-
                 itly, you should call wait to clear up the  corresponding  kernel
                 process slot.  close does not call wait since there is no guaran-
                 tee that closing a process connection will cause it to exit.  See
                 The  debug  command  does  not change any traps.  Compare this to
                 starting Expect with the -D flag (see above).
                 See the README file or SEE ALSO (below) for more  information  on
                 the debugger.
                 disconnects  a  forked  process  from the terminal.  It continues
                 running in the background.  The process is given its own  process
                 group (if possible).  Standard I/O is redirected to /dev/null.
                 The  following  fragment  uses disconnect to continue running the
                 script in the background.
                     if {[fork]!=0} exit
                     . . .
                 The following script reads a password, and then  runs  a  program
                 every  hour  that  demands  a  password each time it is run.  The
                 script supplies the password so that you only  have  to  type  it
                 once.   (See  the stty command which demonstrates how to turn off
                 password echoing.)
                     send_user "password?\ "
                     expect_user -re "(.*)\n"
                     for {} 1 {} {
                         if {[fork]!=0} {sleep 3600;continue}
                         spawn priv_prog
                         expect Password:
                         send "$expect_out(1,string)\r"
                         . . .
                 An advantage to using disconnect over the shell asynchronous pro-
                 cess  feature (&) is that Expect can save the terminal parameters
                 prior to disconnection, and then later apply them  to  new  ptys.
                 With  &,  Expect  does  not  have a chance to read the terminal's
                 parameters since the terminal is already disconnected by the time
                 Expect receives control.
           exit [-opts] [status]
                 causes Expect to exit or otherwise prepare to do so.
                 The  -onexit  flag causes the next argument to be used as an exit
                 handler.  Without  an  argument,  the  current  exit  handler  is
                 The  -noexit flag causes Expect to prepare to exit but stop short
                 mining, for example, what signals a spawned process will be sent,
                 but   these  are  system-dependent,  typically  documented  under
                 exit(3).)  Spawned processes that continue to run will be  inher-
                 ited by init.
                 status  (or 0 if not specified) is returned as the exit status of
                 Expect.  exit is implicitly executed if the end of the script  is
           exp_continue [-continue_timer]
                 The command exp_continue allows expect itself to continue execut-
                 ing rather than  returning  as  it  normally  would.  By  default
                 exp_continue  resets  the timeout timer. The -continue_timer flag
                 prevents timer from being restarted. (See expect for more  infor-
           exp_internal [-f file] value
                 causes  further  commands to send diagnostic information internal
                 to Expect to stderr if value is non-zero.  This  output  is  dis-
                 abled  if  value is 0.  The diagnostic information includes every
                 character received, and every attempt made to match  the  current
                 output against the patterns.
                 If the optional file is supplied, all normal and debugging output
                 is written to that file (regardless of the value of value).   Any
                 previous diagnostic output file is closed.
                 The -info flag causes exp_internal to return a description of the
                 most recent non-info arguments given.
           exp_open [args] [-i spawn_id]
                 returns a Tcl file identifier that corresponds  to  the  original
                 spawn  id.   The  file  identifier can then be used as if it were
                 opened by Tcl's open command.  (The spawn id should no longer  be
                 used.  A wait should not be executed.
                 The  -leaveopen  flag leaves the spawn id open for access through
                 Expect commands.  A wait must be executed on the spawn id.
           exp_pid [-i spawn_id]
                 returns the process id corresponding  to  the  currently  spawned
                 process.  If the -i flag is used, the pid returned corresponds to
                 that of the given spawn id.
                 is an alias for send.
                 is an alias for send_error.
                 is an alias for send_log.
                 specify an earlier version.
                 Versions consist of three numbers separated by  dots.   First  is
                 the  major number.  Scripts written for versions of Expect with a
                 different major number will almost certainly not work.   exp_ver-
                 sion returns an error if the major numbers do not match.
                 Second is the minor number.  Scripts written for a version with a
                 greater minor number than the current  version  may  depend  upon
                 some new feature and might not run.  exp_version returns an error
                 if the major numbers  match,  but  the  script  minor  number  is
                 greater than that of the running Expect.
                 Third  is  a number that plays no part in the version comparison.
                 However, it is incremented when the Expect software  distribution
                 is  changed  in  any  way, such as by additional documentation or
                 optimization.  It is reset to 0 upon each new minor version.
                 With the -exit flag, Expect prints an error and exits if the ver-
                 sion is out of date.
           expect [[-opts] pat1 body1] ... [-opts] patn [bodyn]
                 waits  until  one of the patterns matches the output of a spawned
                 process, a specified time period has passed, or an end-of-file is
                 seen.  If the final body is empty, it may be omitted.
                 Patterns  from  the most recent expect_before command are implic-
                 itly used before any other  patterns.   Patterns  from  the  most
                 recent  expect_after  command are implicitly used after any other
                 If the arguments to the entire expect statement require more than
                 one  line,  all  the  arguments may be "braced" into one so as to
                 avoid terminating each line with a backslash.  In this one  case,
                 the usual Tcl substitutions will occur despite the braces.
                 If  a  pattern is the keyword eof, the corresponding body is exe-
                 cuted upon end-of-file.  If a pattern is the keyword timeout, the
                 corresponding  body is executed upon timeout.  If no timeout key-
                 word is used, an implicit null action is executed  upon  timeout.
                 The  default  timeout  period  is  10 seconds but may be set, for
                 example to 30, by the command  "set  timeout  30".   An  infinite
                 timeout  may  be designated by the value -1.  If a pattern is the
                 keyword default, the corresponding body is executed  upon  either
                 timeout or end-of-file.
                 If  a  pattern  matches, then the corresponding body is executed.
                 expect returns the result of the body (or the empty string if  no
                 pattern matched).  In the event that multiple patterns match, the
                 one appearing first is used to select a body.
                 Each time new output arrives, it is compared to each  pattern  in
                 For example, the following fragment looks for a successful login.
                 (Note  that abort is presumed to be a procedure defined elsewhere
                 in the script.)
                     expect {
                         busy               {puts busy\n ; exp_continue}
                         failed             abort
                         "invalid password" abort
                         timeout            abort
                 Quotes are necessary on the fourth pattern since  it  contains  a
                 space,  which  would  otherwise  separate  the  pattern  from the
                 action.  Patterns with the same action (such as the 3rd and  4th)
                 require  listing  the  actions again.  This can be avoid by using
                 regexp-style patterns (see below).  More information  on  forming
                 glob-style patterns can be found in the Tcl manual.
                 Regexp-style  patterns  follow the syntax defined by Tcl's regexp
                 (short for "regular expression") command.   regexp  patterns  are
                 introduced  with  the  flag  -re.   The  previous  example can be
                 rewritten using a regexp as:
                     expect {
                         busy       {puts busy\n ; exp_continue}
                         -re "failed|invalid password" abort
                         timeout    abort
                 Both types of patterns are "unanchored".  This  means  that  pat-
                 terns  do  not have to match the entire string, but can begin and
                 end the match anywhere in the string (as long as everything  else
                 matches).   Use  ^  to  match the beginning of a string, and $ to
                 match the end.  Note that if you do not wait for  the  end  of  a
                 string,  your  responses  can  easily end up in the middle of the
                 string as they are echoed from the spawned process.  While  still
                 producing  correct results, the output can look unnatural.  Thus,
                 use of $ is encouraged if you can exactly describe the characters
                 at the end of a string.
                 Note  that  in  many editors, the ^ and $ match the beginning and
                 end of lines respectively. However, because expect  is  not  line
                 oriented,  these  characters  match  the beginning and end of the
                 data (as opposed to  lines)  currently  in  the  expect  matching
                 buffer.  (Also, see the note below on "system indigestion.")
                 The  -ex  flag  causes  the  pattern  to be matched as an "exact"
                 string.  No interpretation of *, ^, etc  is  made  (although  the
                 usual  Tcl  conventions  must still be observed).  Exact patterns
                 If  patlist  is  the keyword null, and nulls are allowed (via the
                 remove_nulls command), the corresponding body is  executed  if  a
                 single  ASCII  0 is matched.  It is not possible to match 0 bytes
                 via glob or regexp patterns.
                 Upon matching a pattern (or eof or full_buffer), any matching and
                 previously   unmatched   output   is   saved   in   the  variable
                 expect_out(buffer).  Up to 9 regexp substring matches  are  saved
                 in      the      variables      expect_out(1,string)      through
                 expect_out(9,string).  If the -indices flag is used before a pat-
                 tern,  the  starting  and  ending indices (in a form suitable for
                 lrange)  of  the  10  strings  are  stored   in   the   variables
                 expect_out(X,start)  and  expect_out(X,end)  where  X is a digit,
                 corresponds to the substring position in the buffer.  0 refers to
                 strings  which  matched  the  entire pattern and is generated for
                 glob patterns as well as regexp patterns.  For example, if a pro-
                 cess has produced output of "abcdefgh\n", the result of:
                     expect "cd"
                 is as if the following statements had executed:
                     set expect_out(0,string) cd
                     set expect_out(buffer) abcd
                 and "efgh\n" is left in the output buffer.  If a process produced
                 the output "abbbcabkkkka\n", the result of:
                     expect -indices -re "b(b*).*(k+)"
                 is as if the following statements had executed:
                     set expect_out(0,start) 1
                     set expect_out(0,end) 10
                     set expect_out(0,string) bbbcabkkkk
                     set expect_out(1,start) 2
                     set expect_out(1,end) 3
                     set expect_out(1,string) bb
                     set expect_out(2,start) 10
                     set expect_out(2,end) 10
                     set expect_out(2,string) k
                     set expect_out(buffer) abbbcabkkkk
                 and "a\n" is left in the output buffer.  The pattern "*" (and -re
                 ".*")  will flush the output buffer without reading any more out-
                 put from the process.
                 Normally, the matched output is discarded from Expect's  internal
                 buffers.   This  may be prevented by prefixing a pattern with the
                 -notransfer flag.  This flag is especially useful in  experiment-
                 separated  list  of  spawn_ids  or a variable referring to such a
                 list of spawn_ids.
                 For example, the following example waits for "connected" from the
                 current  process,  or "busy", "failed" or "invalid password" from
                 the spawn_id named by $proc2.
                     expect {
                         -i $proc2 busy {puts busy\n ; exp_continue}
                         -re "failed|invalid password" abort
                         timeout abort
                 The value of the global variable  any_spawn_id  may  be  used  to
                 match  patterns to any spawn_ids that are named with all other -i
                 flags in the current expect command.  The spawn_id from a -i flag
                 with no associated pattern (i.e., followed immediately by another
                 -i) is made available to any other patterns in  the  same  expect
                 command associated with any_spawn_id.
                 The  -i  flag  may  also name a global variable in which case the
                 variable is read for a list of spawn ids.  The variable is reread
                 whenever  it  changes.   This  provides a way of changing the I/O
                 source while the command is in  execution.   Spawn  ids  provided
                 this way are called "indirect" spawn ids.
                 Actions  such  as  break  and  continue  cause control structures
                 (i.e., for, proc) to  behave  in  the  usual  way.   The  command
                 exp_continue  allows  expect  itself to continue executing rather
                 than returning as it normally would.
                 This is useful for avoiding explicit  loops  or  repeated  expect
                 statements.  The following example is part of a fragment to auto-
                 mate rlogin.  The exp_continue avoids having to  write  a  second
                 expect  statement  (to  look  for the prompt again) if the rlogin
                 prompts for a password.
                     expect {
                         Password: {
                             stty -echo
                             send_user "password (for $user) on $host: "
                             expect_user -re "(.*)\n"
                             send_user "\n"
                             send "$expect_out(1,string)\r"
                             stty echo
                         } incorrect {
                             send_user "invalid password or account\n"
                         } timeout {
                             send_user "connection to $host timed out\n"
                 control from the script.  In each case, the  exp_continue  allows
                 the  current  expect to continue pattern matching after executing
                 the current action.
                     stty raw -echo
                     expect_after {
                         -i $user_spawn_id
                         "p" {send "\r\r\r"; exp_continue}
                         "+" {incr foo; exp_continue}
                         "i" {interact; exp_continue}
                         "quit" exit
                 By default, exp_continue resets the timeout timer.  The timer  is
                 not restarted, if exp_continue is called with the -continue_timer
           expect_after [expect_args]
                 works identically to the expect_before except  that  if  patterns
                 from  both  expect and expect_after can match, the expect pattern
                 is used.  See the expect_before command for more information.
           expect_background [expect_args]
                 takes the same arguments as expect, however  it  returns  immedi-
                 ately.  Patterns are tested whenever new input arrives.  The pat-
                 tern timeout and default are meaningless to expect_background and
                 are silently discarded.  Otherwise, the expect_background command
                 uses expect_before and expect_after  patterns  just  like  expect
                 When  expect_background  actions  are being evaluated, background
                 processing for the same spawn id is blocked.  Background process-
                 ing  is  unblocked  when  the action completes.  While background
                 processing is blocked, it is possible to do a (foreground) expect
                 on the same spawn id.
                 It  is  not  possible  to execute an expect while an expect_back-
                 ground is unblocked.  expect_background for a particular spawn id
                 is  deleted  by  declaring  a new expect_background with the same
                 spawn id.  Declaring expect_background with  no  pattern  removes
                 the  given  spawn  id  from  the ability to match patterns in the
           expect_before [expect_args]
                 takes the same arguments as expect, however  it  returns  immedi-
                 ately.   Pattern-action  pairs from the most recent expect_before
                 with the same spawn id are  implicitly  added  to  any  following
                 expect  commands.   If  a pattern matches, it is treated as if it
                 had been specified in the expect command itself, and the  associ-
                 ated  body  is executed in the context of the expect command.  If
                 patterns from  both  expect_before  and  expect  can  match,  the
                     expect_before -info -i $proc
                 At most one spawn id specification may be given.  The flag -indi-
                 rect suppresses direct spawn ids that  come  only  from  indirect
                 Instead  of  a spawn id specification, the flag "-all" will cause
                 "-info" to report on all spawn ids.
                 The output of the -info flag can be reused  as  the  argument  to
           expect_tty [expect_args]
                 is  like  expect  but  it  reads  characters  from /dev/tty (i.e.
                 keystrokes from the user).  By default, reading is  performed  in
                 cooked  mode.   Thus,  lines  must end with a return in order for
                 expect to see them.  This may be changed via stty (see  the  stty
                 command below).
           expect_user [expect_args]
                 is   like  expect  but  it  reads  characters  from  stdin  (i.e.
                 keystrokes from the user).  By default, reading is  performed  in
                 cooked  mode.   Thus,  lines  must end with a return in order for
                 expect to see them.  This may be changed via stty (see  the  stty
                 command below).
           fork  creates  a  new process.  The new process is an exact copy of the
                 current Expect process.  On success, fork returns 0  to  the  new
                 (child)  process  and returns the process ID of the child process
                 to the parent process.  On failure (invariably  due  to  lack  of
                 resources, e.g., swap space, memory), fork returns -1 to the par-
                 ent process, and no child process is created.
                 Forked processes exit via the exit command, just like the  origi-
                 nal  process.   Forked  processes are allowed to write to the log
                 files.  If you do not disable debugging or logging in most of the
                 processes, the result can be confusing.
                 Some  pty implementations may be confused by multiple readers and
                 writers, even momentarily.  Thus, it is  safest  to  fork  before
                 spawning processes.
           interact [string1 body1] ... [stringn [bodyn]]
                 gives  control  of  the  current  process  to  the  user, so that
                 keystrokes are sent to the current process, and  the  stdout  and
                 stderr of the current process are returned.
                 String-body  pairs  may  be specified as arguments, in which case
                 the body is executed when the corresponding  string  is  entered.
                 (By  default,  the  string  is  not sent to the current process.)
                 The interpreter command is assumed, if the final body is missing.
                     set CTRLZ \032
                     interact {
                         -reset $CTRLZ {exec kill -STOP [pid]}
                         \001   {send_user "you typed a control-A\n";
                                 send "\001"
                         $      {send_user "The date is [clock format [clock seconds]]."}
                         \003   exit
                         foo    {send_user "bar"}
                 In string-body pairs, strings are matched in the order  they  are
                 listed  as  arguments.  Strings that partially match are not sent
                 to the current process in anticipation of the  remainder  coming.
                 If characters are then entered such that there can no longer pos-
                 sibly be a match, only the part of the string will be sent to the
                 process  that cannot possibly begin another match.  Thus, strings
                 that are substrings of partial matches can match  later,  if  the
                 original  strings  that  was  attempting  to  be match ultimately
                 By default, string matching is exact with  no  wild  cards.   (In
                 contrast,   the   expect  command  uses  glob-style  patterns  by
                 default.)  The -ex flag may be  used  to  protect  patterns  that
                 might  otherwise match interact flags from doing so.  Any pattern
                 beginning with a  "-"  should  be  protected  this  way.     (All
                 strings starting with "-" are reserved for future options.)
                 The  -re  flag  forces  the string to be interpreted as a regexp-
                 style pattern.  In this case, matching substrings are  stored  in
                 the  variable interact_out similarly to the way expect stores its
                 output in the variable expect_out.  The -indices  flag  is  simi-
                 larly supported.
                 The  pattern  eof introduces an action that is executed upon end-
                 of-file.  A separate eof pattern may also follow the -output flag
                 in  which  case it is matched if an eof is detected while writing
                 output.  The default eof action is  "return",  so  that  interact
                 simply returns upon any EOF.
                 The  pattern timeout introduces a timeout (in seconds) and action
                 that is executed after no characters have been read for  a  given
                 time.  The timeout pattern applies to the most recently specified
                 process.  There is no  default  timeout.   The  special  variable
                 "timeout"  (used  by  the  expect  command) has no affect on this
                 For example, the following statement could be used to  autologout
                 users  who  have not typed anything for an hour but who still get
                 frequent system messages:
                 Actions  such  as  break  and  continue  cause control structures
                 (i.e., for, proc) to behave in the  usual  way.   However  return
                 causes  interact  to  return  to  its  caller, while inter_return
                 causes interact to cause a return in its caller.  For example, if
                 "proc  foo"  called  interact  which  then  executed  the  action
                 inter_return, proc foo would return.  (This means that if  inter-
                 act  calls interpreter interactively typing return will cause the
                 interact to continue, while inter_return will cause the  interact
                 to return to its caller.)
                 During  interact,  raw mode is used so that all characters may be
                 passed to the current process.  If the current process  does  not
                 catch job control signals, it will stop if sent a stop signal (by
                 default ^Z).  To restart it, send a continue signal (such  as  by
                 "kill  -CONT  <pid>").   If  you really want to send a SIGSTOP to
                 such a process (by ^Z), consider spawning csh first and then run-
                 ning  your  program.   On  the  other hand, if you want to send a
                 SIGSTOP to Expect itself,  first  call  interpreter  (perhaps  by
                 using an escape character), and then press ^Z.
                 String-body  pairs can be used as a shorthand for avoiding having
                 to enter the interpreter and execute commands interactively.  The
                 previous  terminal  mode  is used while the body of a string-body
                 pair is being executed.
                 For speed, actions execute in raw mode by  default.   The  -reset
                 flag  resets  the terminal to the mode it had before interact was
                 executed (invariably, cooked mode).  Note that characters entered
                 when  the mode is being switched may be lost (an unfortunate fea-
                 ture of the terminal driver on some systems).  The only reason to
                 use -reset is if your action depends on running in cooked mode.
                 The  -echo flag sends characters that match the following pattern
                 back to the process that generated  them  as  each  character  is
                 read.   This  may  be  useful when the user needs to see feedback
                 from partially typed patterns.
                 If a pattern is being echoed but eventually fails to  match,  the
                 characters  are sent to the spawned process.  If the spawned pro-
                 cess then echoes them, the user will see  the  characters  twice.
                 -echo  is  probably only appropriate in situations where the user
                 is unlikely to not complete the pattern.  For example,  the  fol-
                 lowing  excerpt is from rftp, the recursive-ftp script, where the
                 user is prompted to enter ~g, ~p, or ~l, to get, put, or list the
                 current  directory  recursively.   These are so far away from the
                 normal ftp commands, that the user is unlikely to type ~ followed
                 by anything else, except mistakenly, in which case, they'll prob-
                 ably just ignore the result anyway.
                     interact {
                         -echo ~g {getcurdirectory 1}
                         -echo ~l {getcurdirectory 0}
                     interact -nobuffer "atd" lognumber
                 During interact, previous use of log_user is ignored.  In partic-
                 ular,  interact  will  force its output to be logged (sent to the
                 standard output) since it is presumed the user  doesn't  wish  to
                 interact blindly.
                 The  -o flag causes any following key-body pairs to be applied to
                 the output of the current process.  This can be useful, for exam-
                 ple, when dealing with hosts that send unwanted characters during
                 a telnet session.
                 By default, interact expects the user to  be  writing  stdin  and
                 reading  stdout  of  the Expect process itself.  The -u flag (for
                 "user") makes interact look for the user as the process named  by
                 its argument (which must be a spawned id).
                 This allows two unrelated processes to be joined together without
                 using an explicit loop.  To aid in debugging, Expect  diagnostics
                 always  go to stderr (or stdout for certain logging and debugging
                 information).  For the same reason, the interpreter command  will
                 read interactively from stdin.
                 For  example,  the  following  fragment  creates a login process.
                 Then it dials the user (not shown), and finally connects the  two
                 together.   Of  course, any process may be substituted for login.
                 A shell, for example, would allow the user to work  without  sup-
                 plying an account and password.
                     spawn login
                     set login $spawn_id
                     spawn tip modem
                     # dial back out to user
                     # connect user to login
                     interact -u $login
                 To  send  output  to  multiple processes, list each spawn id list
                 prefaced by a -output flag.  Input for a group  of  output  spawn
                 ids  may  be  determined  by a spawn id list prefaced by a -input
                 flag.  (Both -input and -output may take lists in the  same  form
                 as the -i flag in the expect command, except that any_spawn_id is
                 not meaningful in interact.)  All following flags and strings (or
                 patterns)  apply to this input until another -input flag appears.
                 If no -input  appears,  -output  implies  "-input  $user_spawn_id
                 -output".   (Similarly,  with  patterns that do not have -input.)
                 If one -input is specified, it overrides  $user_spawn_id.   If  a
                 second  -input  is specified, it overrides $spawn_id.  Additional
                 -input flags may be specified.
           interpreter  [args]
                 causes the user to be interactively prompted for Expect  and  Tcl
                 commands.  The result of each command is printed.
                 Actions  such  as  break  and  continue  cause control structures
                 (i.e., for, proc) to behave in the  usual  way.   However  return
                 causes  interpreter  to  return to its caller, while inter_return
                 causes interpreter to cause a return in its caller.  For example,
                 if  "proc  foo" called interpreter which then executed the action
                 inter_return, proc foo would return.  Any  other  command  causes
                 interpreter to continue prompting for new commands.
                 By  default, the prompt contains two integers.  The first integer
                 describes the depth of the evaluation stack (i.e., how many times
                 Tcl_Eval has been called).  The second integer is the Tcl history
                 identifier.  The prompt can be set by defining a procedure called
                 "prompt1"  whose  return  value  becomes  the  next prompt.  If a
                 statement has open quotes, parens, braces, or  brackets,  a  sec-
                 ondary  prompt  (by  default  "+> ") is issued upon newline.  The
                 secondary prompt may  be  set  by  defining  a  procedure  called
                 During  interpreter,  cooked mode is used, even if the its caller
                 was using raw mode.
                 If stdin is closed, interpreter will return unless the -eof  flag
                 is used, in which case the subsequent argument is invoked.
           log_file [args] [[-a] file]
                 If  a  filename is provided, log_file will record a transcript of
                 the session (beginning at that point) in the file.  log_file will
                 stop recording if no argument is given.  Any previous log file is
                 Instead of a filename, a Tcl file identifier may be  provided  by
                 using  the  -open  or  -leaveopen  flags.  This is similar to the
                 spawn command.  (See spawn for more info.)
                 The -a flag forces output to be logged that was suppressed by the
                 log_user command.
                 By default, the log_file command appends to old files rather than
                 truncating them, for the convenience of being able to  turn  log-
                 ging  off  and  on  multiple  times  in one session.  To truncate
                 files, use the -noappend flag.
                 The -info flag causes log_file to return  a  description  of  the
                 most recent non-info arguments given.
           log_user -info|0|1
                 By  default,  the send/expect dialogue is logged to stdout (and a
                 logfile if open).  The logging to stdout is disabled by the  com-
           overlay [-# spawn_id] [-# spawn_id] [...] program [args]
                 executes program args in place of  the  current  Expect  program,
                 which  terminates.   A  bare  hyphen  argument forces a hyphen in
                 front of the command name as  if  it  was  a  login  shell.   All
                 spawn_ids  are closed except for those named as arguments.  These
                 are mapped onto the named file identifiers.
                 Spawn_ids are mapped to file identifiers for the new  program  to
                 inherit.   For  example, the following line runs chess and allows
                 it to be controlled by the current process - say, a chess master.
                     overlay -0 $spawn_id -1 $spawn_id -2 $spawn_id chess
                 This is more efficient than "interact -u", however, it sacrifices
                 the ability to do programmed interaction since the Expect process
                 is no longer in control.
                 Note that no controlling terminal is provided.  Thus, if you dis-
                 connect or remap standard input, programs  that  do  job  control
                 (shells, login, etc) will not function properly.
           parity [-d] [-i spawn_id] [value]
                 defines  whether  parity  should be retained or stripped from the
                 output of  spawned  processes.   If  value  is  zero,  parity  is
                 stripped,  otherwise it is not stripped.  With no value argument,
                 the current value is returned.
                 With the -d flag, the default parity value is set.  (The  initial
                 default  is  1, i.e., parity is not stripped.)  With the -i flag,
                 the parity value is set for the named spawn id, otherwise  it  is
                 set for the current process.
           remove_nulls [-d] [-i spawn_id] [value]
                 defines  whether nulls are retained or removed from the output of
                 spawned processes before pattern matching or storing in the vari-
                 able  expect_out  or  interact_out.   If  value  is  1, nulls are
                 removed.  If value is 0, nulls are not removed.   With  no  value
                 argument, the current value is returned.
                 With the -d flag, the default value is set.  (The initial default
                 is 1, i.e., nulls are removed.)  With the -i flag, the  value  is
                 set  for  the named spawn id, otherwise it is set for the current
                 Whether or not nulls are removed, Expect will record  null  bytes
                 to the log and stdout.
           send [-flags] string
                 Sends string to the current process.  For example, the command
                     send "hello world\r"
                 The -i flag declares  that  the  string  be  sent  to  the  named
                 spawn_id.   If the spawn_id is user_spawn_id, and the terminal is
                 in raw mode, newlines in the string are translated to return-new-
                 line  sequences  so  that  they  appear as if the terminal was in
                 cooked mode.  The -raw flag disables this translation.
                 The -null flag sends null characters (0 bytes).  By default,  one
                 null  is  sent.   An integer may follow the -null to indicate how
                 many nulls to send.
                 The -break flag generates a break  condition.   This  only  makes
                 sense  if  the  spawn id refers to a tty device opened via "spawn
                 -open".  If you have spawned a process such as  tip,  you  should
                 use tip's convention for generating a break.
                 The  -s  flag  forces  output to be sent "slowly", thus avoid the
                 common situation where a computer outtypes an input  buffer  that
                 was designed for a human who would never outtype the same buffer.
                 This  output  is  controlled  by  the  value  of   the   variable
                 "send_slow" which takes a two element list.  The first element is
                 an integer that describes the number of bytes to send atomically.
                 The  second element is a real number that describes the number of
                 seconds by which the atomic sends must be separated.   For  exam-
                 ple,  "set  send_slow  {10  .001}"  would force "send -s" to send
                 strings with 1 millisecond in between each 10 characters sent.
                 The -h flag forces output to be  sent  (somewhat)  like  a  human
                 actually  typing.   Human-like  delays appear between the charac-
                 ters.  (The algorithm is based upon a Weibull distribution,  with
                 modifications  to suit this particular application.)  This output
                 is controlled by the value of  the  variable  "send_human"  which
                 takes  a  five  element list.  The first two elements are average
                 interarrival time of characters in seconds.  The first is used by
                 default.   The  second  is  used at word endings, to simulate the
                 subtle pauses that occasionally occur at such  transitions.   The
                 third  parameter  is  a  measure of variability where .1 is quite
                 variable, 1 is reasonably variable, and 10 is  quite  invariable.
                 The  extremes  are  0  to infinity.  The last two parameters are,
                 respectively, a minimum and maximum interarrival time.  The mini-
                 mum  and  maximum  are  used last and "clip" the final time.  The
                 ultimate average can be quite different from the given average if
                 the minimum and maximum clip enough values.
                 As  an example, the following command emulates a fast and consis-
                 tent typist:
                     set send_human {.1 .3 1 .05 2}
                     send -h "I'm hungry.  Let's do lunch."
                 while the following might be more suitable after a hangover:
                 expect.   expect  will  wait for the process to start, while send
                 cannot.  In particular, if the first send  completes  before  the
                 process  starts  running,  you  run  the risk of having your data
                 ignored.  In situations where interactive programs offer no  ini-
                 tial prompt, you can precede send by a delay as in:
                     # To avoid giving hackers hints on how to break in,
                     # this system does not prompt for an external password.
                     # Wait for 5 seconds for exec to complete
                     spawn telnet
                     sleep 5
                     send password\r
                 exp_send  is an alias for send.  If you are using Expectk or some
                 other variant of Expect in the Tk environment, send is defined by
                 Tk  for  an entirely different purpose.  exp_send is provided for
                 compatibility between environments.  Similar aliases are provided
                 for other Expect's other send commands.
           send_error [-flags] string
                 is  like  send,  except  that the output is sent to stderr rather
                 than the current process.
           send_log [--] string
                 is like send, except that the string is only sent to the log file
                 (see  log_file.)   The  arguments  are  ignored if no log file is
           send_tty [-flags] string
                 is like send, except that the output is sent to  /dev/tty  rather
                 than the current process.
           send_user [-flags] string
                 is  like  send,  except  that the output is sent to stdout rather
                 than the current process.
           sleep seconds
                 causes the script to sleep for the given number of seconds.  Sec-
                 onds  may  be a decimal number.  Interrupts (and Tk events if you
                 are using Expectk) are processed while Expect sleeps.
           spawn [args] program [args]
                 creates a new process running program args.   Its  stdin,  stdout
                 and  stderr are connected to Expect, so that they may be read and
                 written by other Expect commands.  The connection  is  broken  by
                 close  or  if  the  process itself closes any of the file identi-
                 When a process is started by spawn, the variable spawn_id is  set
                 to a descriptor referring to that process.  The process described
                 by spawn_id is considered the current process.  spawn_id  may  be
                 read or written, in effect providing job control.
                     if {[info vars tty_spawn_id]} {
                         # /dev/tty exists
                     } else {
                         # /dev/tty doesn't exist
                         # probably in cron, batch, or at script
                 spawn returns the UNIX process id.  If no process is  spawned,  0
                 is  returned.   The  variable spawn_out(slave,name) is set to the
                 name of the pty slave device.
                 By default, spawn echoes the command  name  and  arguments.   The
                 -noecho flag stops spawn from doing this.
                 The  -console  flag causes console output to be redirected to the
                 spawned process.  This is not supported on all systems.
                 Internally, spawn uses a pty, initialized the  same  way  as  the
                 user's tty.  This is further initialized so that all settings are
                 "sane" (according to stty(1)).   If  the  variable  stty_init  is
                 defined, it is interpreted in the style of stty arguments as fur-
                 ther configuration.  For example, "set stty_init raw" will  cause
                 further  spawned  processes's  terminals  to  start  in raw mode.
                 -nottycopy skips the initialization  based  on  the  user's  tty.
                 -nottyinit skips the "sane" initialization.
                 Normally,  spawn  takes  little  time  to execute.  If you notice
                 spawn taking a significant amount of time, it is probably encoun-
                 tering  ptys  that are wedged.  A number of tests are run on ptys
                 to avoid entanglements with errant  processes.   (These  take  10
                 seconds  per wedged pty.)  Running Expect with the -d option will
                 show if Expect is encountering many ptys in odd states.   If  you
                 cannot  kill the processes to which these ptys are attached, your
                 only recourse may be to reboot.
                 If program cannot be spawned successfully because  exec(2)  fails
                 (e.g.  when  program  doesn't  exist),  an  error message will be
                 returned by the next interact or expect command as if program had
                 run and produced the error message as output.  This behavior is a
                 natural consequence of the implementation of spawn.   Internally,
                 spawn forks, after which the spawned process has no way to commu-
                 nicate with the original Expect process except  by  communication
                 via the spawn_id.
                 The  -open  flag  causes the next argument to be interpreted as a
                 Tcl file identifier (i.e., returned by open.)  The spawn  id  can
                 then  be used as if it were a spawned process.  (The file identi-
                 fier should no longer be used.)  This lets you treat raw devices,
                 files, and pipelines as spawned processes without using a pty.  0
                 is returned to indicate there is no associated process.  When the
                 connection  to  the spawned process is closed, so is the Tcl file
                 named as in the trap command, except that each signal requires  a
                 separate flag.
           strace level
                 causes  following statements to be printed before being executed.
                 (Tcl's trace command traces variables.)  level indicates how  far
                 down in the call stack to trace.  For example, the following com-
                 mand runs Expect while tracing the first 4 levels of  calls,  but
                 none below that.
                     expect -c "strace 4" script.exp
                 The  -info flag causes strace to return a description of the most
                 recent non-info arguments given.
           stty args
                 changes terminal modes similarly to the external stty command.
                 By default, the controlling terminal is accessed.   Other  termi-
                 nals can be accessed by appending "< /dev/tty..." to the command.
                 (Note that the arguments should not  be  grouped  into  a  single
                 Requests  for  status return it as the result of the command.  If
                 no status is requested and the controlling terminal is  accessed,
                 the  previous  status of the raw and echo attributes are returned
                 in a form which can later be used by the command.
                 For example, the arguments raw or -cooked put the  terminal  into
                 raw  mode.   The  arguments  -raw or cooked put the terminal into
                 cooked mode.  The arguments echo and -echo put the terminal  into
                 echo and noecho mode respectively.
                 The  following  example  illustrates  how  to temporarily disable
                 echoing.  This could be used in  otherwise-automatic  scripts  to
                 avoid  embedding passwords in them.  (See more discussion on this
                 under EXPECT HINTS below.)
                     stty -echo
                     send_user "Password: "
                     expect_user -re "(.*)\n"
                     set password $expect_out(1,string)
                     stty echo
           system args
                 gives args to sh(1) as input, just as if it had been typed  as  a
                 command  from  a  terminal.   Expect waits until the shell termi-
                 nates.  The return status from sh is handled the  same  way  that
                 exec handles its return status.
                     %a      abbreviated weekday name
                     %A      full weekday name
                     %b      abbreviated month name
                     %B      full month name
                     %c      date-time as in: Wed Oct  6 11:45:56 1993
                     %d      day of the month (01-31)
                     %H      hour (00-23)
                     %I      hour (01-12)
                     %j      day (001-366)
                     %m      month (01-12)
                     %M      minute (00-59)
                     %p      am or pm
                     %S      second (00-61)
                     %u      day (1-7, Monday is first day of week)
                     %U      week (00-53, first Sunday is first day of week one)
                     %V      week (01-53, ISO 8601 style)
                     %w      day (0-6)
                     %W      week (00-53, first Monday is first day of week one)
                     %x      date-time as in: Wed Oct  6 1993
                     %X      time as in: 23:59:59
                     %y      year (00-99)
                     %Y      year as in: 1993
                     %Z      timezone (or nothing if not determinable)
                     %%      a bare percent sign
                 Other  %  specifications are undefined.  Other characters will be
                 passed through untouched.  Only the C locale is supported.
                 The -seconds flag introduces a number of seconds since the  epoch
                 to be used as a source from which to format.  Otherwise, the cur-
                 rent time is used.
                 The -gmt flag forces timestamp output to use  the  GMT  timezone.
                 With no flag, the local timezone is used.
           trap [[command] signals]
                 causes  the  given  command to be executed upon future receipt of
                 any of the given signals.  The command is executed in the  global
                 scope.   If command is absent, the signal action is returned.  If
                 command is the string SIG_IGN, the signals are ignored.  If  com-
                 mand  is the string SIG_DFL, the signals are result to the system
                 default.  signals is either a single signal or a list of signals.
                 Signals  may be specified numerically or symbolically as per sig-
                 nal(3).  The "SIG" prefix may be omitted.
                 With no arguments (or the argument  -number),  trap  returns  the
                 signal number of the trap command currently being executed.
                 The  -code  flag  uses the return code of the command in place of
                 whatever code Tcl was about to return when the command originally
                 started running.
                 ^C) and SIGTERM cause Expect to exit.  This is due to the follow-
                 ing trap, created by default when Expect starts.
                     trap exit {SIGINT SIGTERM}
                 If you use the -D flag to start the debugger, SIGINT is redefined
                 to  start the interactive debugger.  This is due to the following
                     trap {exp_debug 1} SIGINT
                 The debugger trap can be changed by setting the environment vari-
                 able EXPECT_DEBUG_INIT to a new trap command.
                 You  can,  of  course, override both of these just by adding trap
                 commands to your script.  In particular, if  you  have  your  own
                 "trap  exit  SIGINT", this will override the debugger trap.  This
                 is useful if you want to prevent users from getting to the debug-
                 ger at all.
                 If  you  want to define your own trap on SIGINT but still trap to
                 the debugger when it is running, use:
                     if {![exp_debug]} {trap mystuff SIGINT}
                 Alternatively, you can trap to the debugger using some other sig-
                 trap  will not let you override the action for SIGALRM as this is
                 used internally to Expect.  The disconnect command  sets  SIGALRM
                 to  SIG_IGN  (ignore).  You can reenable this as long as you dis-
                 able it during subsequent spawn commands.
                 See signal(3) for more info.
           wait [args]
                 delays until a spawned process (or the current process if none is
                 named) terminates.
                 wait normally returns a list of four integers.  The first integer
                 is the pid of the process that was waited upon.  The second inte-
                 ger is the corresponding spawn id.  The third integer is -1 if an
                 operating system error occurred, or 0 otherwise.   If  the  third
                 integer  was  0, the fourth integer is the status returned by the
                 spawned process.  If the third integer was -1, the fourth integer
                 is  the  value  of errno set by the operating system.  The global
                 variable errorCode is also set.
                 Additional elements may appear at the end  of  the  return  value
                 from  wait.   An  optional  fifth  element  identifies a class of
                 information.  Currently, the only possible value for this element
                 is  CHILDKILLED in which case the next two values are the C-style
                 this command can be executed at any time.  There  is  no  control
                 over  which  process is reaped.  However, the return value can be
                 checked for the process id.


           Expect automatically knows about  two  built-in  libraries  for  Expect
           scripts.   These  are defined by the directories named in the variables
           exp_library and exp_exec_library.  Both are meant  to  contain  utility
           files that can be used by other scripts.
           exp_library  contains architecture-independent files.  exp_exec_library
           contains architecture-dependent files.  Depending on your system,  both
           directories   may   be  totally  empty.   The  existence  of  the  file
           $exp_exec_library/cat-buffers describes whether your  /bin/cat  buffers
           by default.


           A  vgrind  definition  is available for pretty-printing Expect scripts.
           Assuming the vgrind definition supplied with the Expect distribution is
           correctly installed, you can use it as:
               vgrind -lexpect file


           It  many  not  be  apparent how to put everything together that the man
           page describes.  I encourage you to read and try out  the  examples  in
           the  example  directory  of  the Expect distribution.  Some of them are
           real programs.  Others are simply illustrative of  certain  techniques,
           and  of  course, a couple are just quick hacks.  The INSTALL file has a
           quick overview of these programs.
           The Expect papers (see SEE ALSO) are also useful.   While  some  papers
           use  syntax corresponding to earlier versions of Expect, the accompany-
           ing rationales are still valid and go into a lot more detail than  this
           man page.


           Extensions  may collide with Expect's command names.  For example, send
           is defined by Tk for an entirely different purpose.  For  this  reason,
           most of the Expect commands are also available as "exp_XXXX".  Commands
           and variables beginning with "exp", "inter", "spawn", and "timeout"  do
           not have aliases.  Use the extended command names if you need this com-
           patibility between environments.
           Expect takes a rather liberal view of scoping.   In  particular,  vari-
           ables  read  by  commands specific to the Expect program will be sought
           first from the local scope, and if not found, in the global scope.  For
           example, this obviates the need to place "global timeout" in every pro-
           cedure you write that uses expect.  On the other hand, variables  writ-
           ten  are  always in the local scope (unless a "global" command has been
           a script is written to look for echoing, it will misbehave  if  echoing
           is turned off.  For this reason, Expect forces sane terminal parameters
           by default.  Unfortunately, this can make things unpleasant  for  other
           programs.   As  an example, the emacs shell wants to change the "usual"
           mappings: newlines get mapped to newlines  instead  of  carriage-return
           newlines,  and  echoing  is  disabled.  This allows one to use emacs to
           edit the input line.  Unfortunately, Expect cannot possibly guess this.
           You  can request that Expect not override its default setting of termi-
           nal parameters, but you must then be very careful when writing  scripts
           for  such  environments.   In  the  case of emacs, avoid depending upon
           things like echoing and end-of-line mappings.
           The commands that accepted arguments braced into  a  single  list  (the
           expect  variants and interact) use a heuristic to decide if the list is
           actually one argument or many.  The heuristic can fail only in the case
           when  the list actually does represent a single argument which has mul-
           tiple embedded \n's with non-whitespace characters between them.   This
           seems  sufficiently  improbable, however the argument "-nobrace" can be
           used to force a single argument to be handled  as  a  single  argument.
           This  could  conceivably  be  used  with machine-generated Expect code.
           Similarly, -brace forces a single argument to  be  handle  as  multiple


           It  was  really  tempting  to name the program "sex" (for either "Smart
           EXec" or "Send-EXpect"), but good sense (or  perhaps  just  Puritanism)
           On  some systems, when a shell is spawned, it complains about not being
           able to access the tty but runs anyway.  This means your system  has  a
           mechanism  for  gaining  the  controlling  tty that Expect doesn't know
           about.  Please find out what it is, and send this information  back  to
           Ultrix  4.1  (at least the latest versions around here) considers time-
           outs of above 1000000 to be equivalent to 0.
           Digital UNIX 4.0A (and probably other  versions)  refuses  to  allocate
           ptys  if you define a SIGCHLD handler.  See grantpt page for more info.
           IRIX 6.0 does not handle pty permissions correctly so  that  if  Expect
           attempts  to  allocate a pty previously used by someone else, it fails.
           Upgrade to IRIX 6.1.
           Telnet (verified only under SunOS 4.1.2) hangs  if  TERM  is  not  set.
           This  is  a  problem  under  cron,  at and in cgi scripts, which do not
           define TERM.  Thus, you must set it explicitly - to what type  is  usu-
           ally  irrelevant.   It  just has to be set to something!  The following
           probably suffices for most cases.
           Some implementations of ptys are designed so  that  the  kernel  throws
           away  any unread output after 10 to 15 seconds (actual number is imple-
           mentation-dependent) after the process has closed the file  descriptor.
           Thus Expect programs such as
               spawn date
               sleep 20
           will  fail.   To  avoid this, invoke non-interactive programs with exec
           rather than spawn.  While such situations are conceivable, in  practice
           I  have  never  encountered  a situation in which the final output of a
           truly interactive program would be lost due to this behavior.
           On the other hand, Cray UNICOS ptys throw away any unread output  imme-
           diately  after  the  process  has  closed  the file descriptor.  I have
           reported this to Cray and they are working on a fix.
           Sometimes a delay is required between a prompt and a response, such  as
           when  a  tty interface is changing UART settings or matching baud rates
           by looking for start/stop bits.  Usually, all this  is  require  is  to
           sleep  for  a second or two.  A more robust technique is to retry until
           the hardware is ready to receive input.   The  following  example  uses
           both strategies:
               send "speed 9600\r";
               sleep 1
               expect {
                   timeout {send "\r"; exp_continue}
           trap  -code  will  not  work  with any command that sits in Tcl's event
           loop, such as sleep.  The problem is that in the event loop,  Tcl  dis-
           cards  the  return codes from async event handlers.  A workaround is to
           set a flag in the trap code.  Then check the flag immediately after the
           command (i.e., sleep).
           The  expect_background  command  ignores  -timeout arguments and has no
           concept of timeouts in general.


           There are a couple of things about Expect that  may  be  non-intuitive.
           This  section attempts to address some of these things with a couple of
           A common expect problem is how to recognize shell prompts.  Since these
           are  customized differently by differently people and different shells,
           portably automating rlogin can be difficult without knowing the prompt.
           A  reasonable  convention  is  to have users store a regular expression
           answer  early,  your answer may appear echoed back in the middle of the
           question.  In other words, the resulting dialogue will be  correct  but
           look scrambled.
           Most  prompts  include  a space character at the end.  For example, the
           prompt from ftp is 'f', 't', 'p',  '>'  and  <blank>.   To  match  this
           prompt,  you must account for each of these characters.  It is a common
           mistake not to include the blank.  Put the blank in explicitly.
           If you use a pattern of the form X*, the * will match  all  the  output
           received  from  the  end  of X to the last thing received.  This sounds
           intuitive but can be somewhat confusing because the phrase "last  thing
           received"  can  vary  depending  upon the speed of the computer and the
           processing of I/O both by the kernel and the device driver.
           In particular, humans tend to  see  program  output  arriving  in  huge
           chunks  (atomically)  when  in reality most programs produce output one
           line at a time.  Assuming this is the case, the * in the pattern of the
           previous  paragraph  may  only  match  the end of the current line even
           though there seems to be more, because at the time of  the  match  that
           was all the output that had been received.
           expect  has no way of knowing that further output is coming unless your
           pattern specifically accounts for it.
           Even depending on line-oriented buffering is unwise.  Not only do  pro-
           grams  rarely  make  promises  about the type of buffering they do, but
           system indigestion can break output lines up so  that  lines  break  at
           seemingly  random  places.   Thus,  if  you  can  express  the last few
           characters of a prompt when writing patterns, it is wise to do so.
           If you are waiting for a pattern in the last output of  a  program  and
           the  program  emits  something  else  instead,  you will not be able to
           detect that with the timeout keyword.  The reason is that  expect  will
           not timeout - instead it will get an eof indication.  Use that instead.
           Even better, use both.  That way if that line is ever moved around, you
           won't have to edit the line itself.
           Newlines  are  usually converted to carriage return, linefeed sequences
           when output by the terminal driver.  Thus, if you want a  pattern  that
           explicitly  matches  the  two lines, from, say, printf("foo\nbar"), you
           should use the pattern "foo\r\nbar".
           A  similar  translation  occurs  when  reading  from  the   user,   via
           expect_user.   In  this  case, when you press return, it will be trans-
           lated to a newline.  If Expect then passes that to a program which sets
           its terminal to raw mode (like telnet), there is going to be a problem,
           as the program expects a true return.  (Some programs are actually for-
           giving  in  that they will automatically translate newlines to returns,
           but most don't.)  Unfortunately, there is no way to  find  out  that  a
           program put its terminal into raw mode.
           Unfortunately, the UNIX file system  has  no  direct  way  of  creating
           scripts  which  are  executable  but unreadable.  Systems which support
           setgid shell scripts may indirectly simulate this as follows:
           Create the Expect script (that contains  the  secret  data)  as  usual.
           Make  its permissions be 750 (-rwxr-x---) and owned by a trusted group,
           i.e., a group which is allowed to read it.  If necessary, create a  new
           group for this purpose.  Next, create a /bin/sh script with permissions
           2751 (-rwxr-s--x) owned by the same group as before.
           The result is a script which may be  executed  (and  read)  by  anyone.
           When invoked, it runs the Expect script.


           Tcl(3), libexpect(3)
           "Exploring  Expect: A Tcl-Based Toolkit for Automating Interactive Pro-
           grams" by Don Libes, pp. 602, ISBN 1-56592-090-2,  O'Reilly  and  Asso-
           ciates, 1995.
           "expect:  Curing  Those  Uncontrollable  Fits  of Interactivity" by Don
           Libes, Proceedings of the Summer 1990 USENIX Conference, Anaheim, Cali-
           fornia, June 11-15, 1990.
           "Using  expect  to  Automate System Administration Tasks" by Don Libes,
           Proceedings of the 1990 USENIX Large Installation  Systems  Administra-
           tion Conference, Colorado Springs, Colorado, October 17-19, 1990.
           "Tcl:  An  Embeddable Command Language" by John Ousterhout, Proceedings
           of the Winter 1990 USENIX Conference, Washington, D.C., January  22-26,
           "expect:  Scripts  for  Controlling Interactive Programs" by Don Libes,
           Computing Systems, Vol. 4, No. 2, University of California Press  Jour-
           nals, November 1991.
           "Regression  Testing  and Conformance Testing Interactive Programs", by
           Don Libes, Proceedings  of  the  Summer  1992  USENIX  Conference,  pp.
           135-144, San Antonio, TX, June 12-15, 1992.
           "Kibitz  -  Connecting  Multiple Interactive Programs Together", by Don
           Libes, Software - Practice & Experience, John Wiley & Sons,  West  Sus-
           sex, England, Vol. 23, No. 5, May, 1993.
           "A  Debugger  for  Tcl  Applications", by Don Libes, Proceedings of the
           1993 Tcl/Tk Workshop, Berkeley, CA, June 10-11, 1993.


           Don Libes, National Institute of Standards and Technology


           Thanks to John Ousterhout for Tcl, and Scott Paisley  for  inspiration.
           Thanks to Rob Savoye for Expect's autoconfiguration code.
           The  HISTORY  file documents much of the evolution of expect.  It makes
           interesting reading and might give you further insight  to  this  soft-
           ware.   Thanks  to the people mentioned in it who sent me bug fixes and
           gave other assistance.

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