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EXPECT(1)                                                            EXPECT(1)



NAME
       expect - programmed dialogue with interactive programs, Version 5

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

INTRODUCTION
       Expect  is  a  program that "talks" to other interactive programs according to a script.  Following the script,
       Expect knows what can be expected from a program and what the correct response should be.  An interpreted  lan-
       guage  provides  branching and high-level control structures to direct the dialogue.  In addition, the user can
       take control and interact directly when desired, afterward returning control to the script.

       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 popularized by uucp, kermit and other modem con-
       trol programs.  However unlike uucp, Expect is generalized so that it can be run as a user-level  command  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 criteria.

              ?   Connect  to another network or BBS (e.g., MCI Mail, CompuServe) 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 controlled) if desired.  Similarly, the user  can
       return control to the script at any time.

USAGE
       Expect reads cmdfile for a list of commands to execute.  Expect may also be invoked implicitly on systems which
       support the #! notation by marking the script executable, and making the first line in your script:

           #!/usr/local/bin/expect -f

       Of course, the path must accurately describe where Expect lives.  /usr/local/bin is just an example.

       The -c flag prefaces a command to be executed before any in the script.  The command should be quoted  to  pre-
       vent  being broken up by the shell.  This option may be used multiple times.  Multiple commands may be executed
       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 informa-
       tion 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 arbitrary files to be
       handled this way, use the -b flag.  (When using Expectk, this option  is  specified  as  -buffer.)   Note  that
       stdio-buffering 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 command 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  (includ-
       ing 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.

       The file $exp_library/expect.rc is sourced automatically if present, unless the -N flag is used.   (When  using
       Expectk, this option is specified as -NORC.)  Immediately after this, the file ~/.expect.rc is sourced automat-
       ically, unless the -n flag is used.  If the environment variable DOTDIR is defined, it is treated as  a  direc-
       tory  and .expect.rc is read from there.  (When using Expectk, this option is specified as -norc.)  This sourc-
       ing occurs only after executing any -c flags.

       -v causes Expect to print its version number and exit.  (The corresponding flag in  Expectk,  which  uses  long
       flag names, is -version.)

       Optional  args  are  constructed into a list and stored in the variable named argv.  argc is initialized to the
       length of argv.

       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"


COMMANDS
       Expect  uses Tcl (Tool Command Language).  Tcl provides control flow (e.g., if, for, break), expression evalua-
       tion and several other features 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 descriptions 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).  Examples 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 usually 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 explicitly, you should call wait to clear up the
             corresponding  kernel  process slot.  close does not call wait since there is no guarantee that closing a
             process connection will cause it to exit.  See wait below for more info.

       debug [[-now] 0|1]
             controls a Tcl debugger allowing you to step through statements, set breakpoints, etc.

             With no arguments, a 1 is returned if the debugger is not running, otherwise a 0 is returned.

             With a 1 argument, the debugger is started.  With a 0 argument, the debugger is stopped.  If a 1 argument
             is  preceded by the -now flag, the debugger is started immediately (i.e., in the middle of the debug com-
             mand itself).  Otherwise, the debugger is started with the next Tcl statement.

             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.

       disconnect
             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
                 disconnect
                 . . .

             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}
                     disconnect
                     spawn priv_prog
                     expect Password:
                     send "$expect_out(1,string)\r"
                     . . .
                     exit
                 }

             An advantage to using disconnect over the shell asynchronous process 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 cur-
             rent exit handler is returned.

             The -noexit flag causes Expect to prepare to exit but stop short of actually  returning  control  to  the
             operating  system.   The  user-defined exit handler is run as well as Expect's own internal handlers.  No
             further Expect commands should be executed.  This is useful if you are  running  Expect  with  other  Tcl
             extensions.   The current interpreter (and main window if in the Tk environment) remain so that other Tcl
             extensions can clean up.  If Expect's exit is called again (however this might occur), the  handlers  are
             not rerun.

             Upon  exiting,  all  connections  to spawned processes are closed.  Closure will be detected as an EOF by
             spawned processes.  exit takes no other actions beyond what the normal _exit(2)  procedure  does.   Thus,
             spawned  processes that do not check for EOF may continue to run.  (A variety of conditions are important
             to determining, 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 inherited 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 reached.

       exp_continue [-continue_timer]
             The command exp_continue allows expect itself to continue executing 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 information.)

       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 disabled 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.

       exp_send
             is an alias for send.

       exp_send_error
             is an alias for send_error.

       exp_send_log
             is an alias for send_log.

       exp_send_tty
             is an alias for send_tty.

       exp_send_user
             is an alias for send_user.

       exp_version [[-exit] version]
             is useful for assuring that the script is compatible with the current version of Expect.

             With  no  arguments, the current version of Expect is returned.  This version may then be encoded in your
             script.  If you actually know that you are not using features of recent versions, you can specify an ear-
             lier 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_version 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 version 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 implicitly used before any other patterns.   Pat-
             terns from the most recent expect_after command are implicitly used after any other patterns.

             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 executed upon end-of-file.  If a pattern is
             the keyword timeout, the corresponding body is executed upon timeout.  If no timeout keyword 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 the order they are listed.  Thus, you may
             test  for absence of a match by making the last pattern something guaranteed to appear, such as a prompt.
             In situations where there is no prompt, you must use timeout (just like you would if you were interacting
             manually).

             Patterns are specified in three ways.  By default, patterns are specified as with Tcl's string match com-
             mand.  (Such patterns are also similar to C-shell regular expressions usually referred to as "glob"  pat-
             terns).   The  -gl  flag may may be used to protect patterns that might otherwise match expect flags from
             doing so.  Any pattern beginning with a "-" should be protected this way.  (All strings starting with "-"
             are reserved for future options.)


             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
                     connected
                 }

             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  form-
             ing 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
                     connected
                 }

             Both  types  of  patterns  are  "unanchored".   This  means that patterns 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 are always unanchored.


             The -nocase flag causes uppercase characters of the output to compare as if they were  lowercase  charac-
             ters.  The pattern is not affected.

             While  reading  output,  more  than  2000  bytes  can force earlier bytes to be "forgotten".  This may be
             changed with the function match_max.  (Note that excessively large  values  can  slow  down  the  pattern
             matcher.)   If  patlist  is  full_buffer, the corresponding body is executed if match_max bytes have been
             received and no other patterns have matched.  Whether or not the full_buffer keyword is used, the forgot-
             ten characters are written to expect_out(buffer).

             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 pattern, 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 process 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 output from the process.

             Normally,  the matched output is discarded from Expect's internal buffers.  This may be prevented by pre-
             fixing a pattern with the -notransfer flag.  This flag is especially useful in experimenting (and can  be
             abbreviated to "-not" for convenience while experimenting).

             The   spawn   id   associated   with   the   matching  output  (or  eof  or  full_buffer)  is  stored  in
             expect_out(spawn_id).

             The -timeout flag causes the current expect command to use the following value as a  timeout  instead  of
             using the value of the timeout variable.

             By  default,  patterns  are matched against output from the current process, however the -i flag declares
             the output from the named spawn_id list be matched against any following patterns (up to  the  next  -i).
             The  spawn_id  list  should either be a whitespace 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
                     connected
                 }

             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 associ-
             ated  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 automate 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
                         exp_continue
                     } incorrect {
                         send_user "invalid password or account\n"
                         exit
                     } timeout {
                         send_user "connection to $host timed out\n"
                         exit
                     } eof {
                         send_user \
                             "connection to host failed: $expect_out(buffer)"
                         exit
                     } -re $prompt
                 }

             For example, the following fragment might help a user guide an interaction that is already totally  auto-
             mated.   In  this case, the terminal is put into raw mode.  If the user presses "+", a variable is incre-
             mented.  If "p" is pressed, several returns are sent to the process, perhaps to poke it in some way,  and
             "i"  lets the user interact with the process, effectively stealing away 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 flag.

       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 immediately.  Patterns are tested whenever new
             input arrives.  The pattern 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 does.

             When expect_background actions are being evaluated, background  processing  for  the  same  spawn  id  is
             blocked.   Background  processing 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_background 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
             background.

       expect_before [expect_args]
             takes  the  same arguments as expect, however it returns immediately.  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 pattern is used.

             If no pattern is specified, the spawn id is not checked for any patterns.

             Unless  overridden  by  a  -i flag, expect_before patterns match against the spawn id defined at the time
             that the expect_before command was executed (not when its pattern is matched).

             The -info flag causes expect_before to return the current specifications of what patterns it will  match.
             By  default,  it  reports  on  the current spawn id.  An optional spawn id specification may be given for
             information on that spawn id.  For example

                 expect_before -info -i $proc

             At most one spawn id specification may be given.  The flag -indirect suppresses  direct  spawn  ids  that
             come only from indirect specifications.

             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_before.

       expect_tty [expect_args]
             is  like expect but it reads characters from /dev/tty (i.e. keystrokes from the user).  By default, read-
             ing 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  pro-
             cess.  On failure (invariably due to lack of resources, e.g., swap space, memory), fork returns -1 to the
             parent process, and no child process is created.

             Forked processes exit via the exit command, just like the original 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  correspond-
             ing  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.

             If the arguments to the entire interact 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.

             For example, the following command runs interact with the following string-body pairs defined:   When  ^Z
             is pressed, Expect is suspended.  (The -reset flag restores the terminal modes.)  When ^A is pressed, the
             user sees "you typed a control-A" and the process is sent a ^A.  When $ is pressed,  the  user  sees  the
             date.   When ^C is pressed, Expect exits.  If "foo" is entered, the user sees "bar".  When ~~ is pressed,
             the Expect interpreter runs interactively.

                 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  par-
             tially  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 possibly 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 par-
             tial matches can match later, if the original strings that was attempting to be match ultimately fails.

             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 sub-
             strings are stored in the variable interact_out similarly to the way expect  stores  its  output  in  the
             variable expect_out.  The -indices flag is similarly 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 timeout.

             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:

                 interact -input $user_spawn_id timeout 3600 return -output \
                     $spawn_id


             If the pattern is the keyword null, and nulls are allowed (via the remove_nulls command), the correspond-
             ing body is executed if a single ASCII 0 is matched.  It is not possible to match 0  bytes  via  glob  or
             regexp patterns.

             Prefacing  a  pattern  with  the flag -iwrite causes the variable interact_out(spawn_id) to be set to the
             spawn_id which matched the pattern (or eof).

             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 interact 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 running  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 feature 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 pro-
             cess.  If the spawned process then echoes them, the user will see the characters twice.  -echo is  proba-
             bly  only appropriate in situations where the user is unlikely to not complete the pattern.  For example,
             the following 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 probably just ignore the result anyway.

                 interact {
                     -echo ~g {getcurdirectory 1}
                     -echo ~l {getcurdirectory 0}
                     -echo ~p {putcurdirectory}
                 }

             The  -nobuffer flag sends characters that match the following pattern on to the output process as charac-
             ters are read.

             This is useful when you wish to let a program echo back the pattern.  For example, the following might be
             used to monitor where a person is dialing (a Hayes-style modem).  Each time "atd" is seen the script logs
             the rest of the line.

                 proc lognumber {} {
                     interact -nobuffer -re "(.*)\r" return
                     puts $log "[clock format [clock seconds]]: dialed $interact_out(1,string)"
                 }

                 interact -nobuffer "atd" lognumber


             During interact, previous use of log_user is ignored.  In particular, 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 example, when dealing with hosts that send unwanted characters during  a  telnet  ses-
             sion.

             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  informa-
             tion).  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 supplying 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.

             The two implied input processes default to having their outputs specified as $spawn_id and $user_spawn_id
             (in reverse).  If a -input flag appears with no -output flag, characters from that process are discarded.

             The -i flag introduces a replacement for the current spawn_id when no other -input or -output  flags  are
             used.  A -i flag implies a -o flag.

             It  is  possible  to  change  the  processes  that are being interacted with by using indirect spawn ids.
             (Indirect spawn ids are described in the section on the expect command.)  Indirect spawn ids may be spec-
             ified with the -i, -u, -input, or -output flags.

       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 secondary prompt (by default "+>
             ") is issued upon newline.  The secondary prompt may be set by defining a procedure called "prompt2".

             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 closed.

             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 logging off and on multiple times in one session.  To truncate files, use  the  -noap-
             pend 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 command "log_user 0" and reenabled  by  "log_user  1".   Logging  to  the  logfile  is
             unchanged.

             The -info flag causes log_user to return a description of the most recent non-info arguments given.

       match_max [-d] [-i spawn_id] [size]
             defines  the size of the buffer (in bytes) used internally by expect.  With no size argument, the current
             size is returned.

             With the -d flag, the default size is set.  (The initial default is 2000.)  With the -i flag, the size is
             set for the named spawn id, otherwise it is set for the current process.

       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  interac-
             tion since the Expect process is no longer in control.

             Note that no controlling terminal is provided.  Thus, if you disconnect 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  match-
             ing  or  storing in the variable 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 process.

             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"

             sends  the  characters,  h  e  l  l o <blank> w o r l d <return> to the current process.  (Tcl includes a
             printf-like command (called format) which can build arbitrarily complex strings.)

             Characters are sent immediately although programs with line-buffered input will not read  the  characters
             until a return character is sent.  A return character is denoted "\r".

             The -- flag forces the next argument to be interpreted as a string rather than a flag.  Any string can be
             preceded by "--" whether or not it actually looks like a flag.  This provides  a  reliable  mechanism  to
             specify  variable  strings  without  being  tripped  up by those that accidentally look like flags.  (All
             strings starting with "-" are reserved for future options.)

             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-newline 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 conven-
             tion 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 example, "set
             send_slow {10 .001}" would force "send -s" to send strings with 1 millisecond in between each 10  charac-
             ters sent.

             The  -h  flag forces output to be sent (somewhat) like a human actually typing.  Human-like delays appear
             between the characters.  (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  sec-
             onds.   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 minimum and max-
             imum 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 consistent 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:

                 set send_human {.4 .4 .2 .5 100}
                 send -h "Goodd party lash night!"

             Note that errors are not simulated, although you can set  up  error  correction  situations  yourself  by
             embedding mistakes and corrections in a send argument.

             The  flags  for  sending null characters, for sending breaks, for forcing slow output and for human-style
             output are mutually exclusive. Only the one specified last will be used. Furthermore, no string  argument
             can be specified with the flags for sending null characters or breaks.

             It  is a good idea to precede the first send to a process by an expect.  expect will wait for the process
             to start, while send cannot.  In particular, if the first send completes before the process  starts  run-
             ning,  you  run  the risk of having your data ignored.  In situations where interactive programs offer no
             initial 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 very.secure.gov
                 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  envi-
             ronment, 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 open.

       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.  Seconds 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 identifiers.

             When a process is started by spawn, the variable spawn_id is set to a descriptor referring to  that  pro-
             cess.   The  process  described  by  spawn_id is considered the current process.  spawn_id may be read or
             written, in effect providing job control.

             user_spawn_id is a global variable containing a descriptor which refers to the user.  For  example,  when
             spawn_id is set to this value, expect behaves like expect_user.

             error_spawn_id  is  a  global  variable  containing a descriptor which refers to the standard error.  For
             example, when spawn_id is set to this value, send behaves like send_error.

             tty_spawn_id is a global variable containing a descriptor which refers to /dev/tty.  If /dev/tty does not
             exist (such as in a cron, at, or batch script), then tty_spawn_id is not defined.  This may be tested as:

                 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 inter-
             preted in the style of stty arguments as further 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 encountering ptys that are wedged.  A number of tests are run on ptys to avoid entangle-
             ments 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 communicate 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 identifier 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 identifier.  The -leaveopen flag is similar to -open except
             that -leaveopen causes the file identifier to be left open even after the spawn id is closed.

             The  -pty  flag  causes a pty to be opened but no process spawned.  0 is returned to indicate there is no
             associated process.  Spawn_id is set as usual.

             The variable spawn_out(slave,fd) is set to a file identifier corresponding to the pty slave.  It  can  be
             closed using "close -slave".

             The -ignore flag names a signal to be ignored in the spawned process.  Otherwise, signals get the default
             behavior.  Signals are 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 command 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  terminals  can  be  accessed  by  appending  "<
             /dev/tty..." to the command.  (Note that the arguments should not be grouped into a single argument.)

             Requests  for  status return it as the result of the command.  If no status is requested and the control-
             ling 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 terminates.  The return status from sh is handled the same  way  that  exec  handles  its
             return status.

             In contrast to exec which redirects stdin and stdout to the script, system performs no redirection (other
             than that indicated by the string itself).  Thus, it is possible to use programs which must talk directly
             to /dev/tty.  For the same reason, the results of system are not recorded in the log.

       timestamp [args]
             returns a timestamp.  With no arguments, the number of seconds since the epoch is returned.

             The -format flag introduces a string which is returned but with substitutions made according to the POSIX
             rules for strftime.  For example %a is replaced by an abbreviated weekday name (i.e., Sat).  Others are:
                 %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 current 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 command 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 numer-
             ically or symbolically as per signal(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.

             The  -interp flag causes the command to be evaluated using the interpreter active at the time the command
             started running rather than when the trap was declared.

             The -name flag causes the trap command to return the signal name of the trap command currently being exe-
             cuted.

             The -max flag causes the trap command to return the largest signal number that can be set.

             For example, the command "trap {send_user "Ouch!"} SIGINT" will print "Ouch!"  each time the user presses
             ^C.

             By default, SIGINT (which can usually be generated by pressing ^C) and  SIGTERM  cause  Expect  to  exit.
             This is due to the following 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:

                 trap {exp_debug 1} SIGINT

             The debugger trap can be changed by setting the environment variable EXPECT_DEBUG_INIT to a new trap com-
             mand.

             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 debugger 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 signal.

             trap  will not let you override the action for SIGALRM as this is used internally to Expect.  The discon-
             nect command sets SIGALRM to SIG_IGN (ignore).  You can reenable this as long as you  disable  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 integer 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 iden-
             tifies 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 signal name and a short textual description.

             The  -i  flag  declares  the  process  to  wait corresponding to the named spawn_id (NOT the process id).
             Inside a SIGCHLD handler, it is possible to wait for any spawned process by using the spawn id -1.

             The -nowait flag causes the wait to return immediately with the indication of a  successful  wait.   When
             the process exits (later), it will automatically disappear without the need for an explicit wait.

             The  wait command may also be used wait for a forked process using the arguments "-i -1".  Unlike its use
             with spawned processes, 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.


LIBRARIES
       Expect  automatically knows about two built-in libraries for Expect scripts.  These are defined by the directo-
       ries 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.

PRETTY-PRINTING
       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


EXAMPLES
       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 ver-
       sions of Expect, the accompanying rationales are still valid and go into a lot more detail than this man  page.

CAVEATS
       Extensions may collide with Expect's command names.  For example, send is defined by Tk for an entirely differ-
       ent 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 compatibility between environments.

       Expect takes a rather liberal view of scoping.  In particular, variables  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 procedure you write that uses expect.  On  the  other
       hand,  variables  written  are always in the local scope (unless a "global" command has been issued).  The most
       common problem this causes is when spawn is executed in a procedure.  Outside the procedure, spawn_id no longer
       exists,  so  the spawned process is no longer accessible simply because of scoping.  Add a "global spawn_id" to
       such a procedure.

       If you cannot enable the multispawning capability (i.e., your system supports neither select  (BSD  *.*),  poll
       (SVR>2),  nor  something  equivalent), Expect will only be able to control a single process at a time.  In this
       case, do not attempt to set spawn_id, nor should you execute processes via exec while a spawned process is run-
       ning.   Furthermore,  you will not be able to expect from multiple processes (including the user as one) at the
       same time.

       Terminal parameters can have a big effect on scripts.  For example, if 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 possi-
       bly guess this.

       You  can request that Expect not override its default setting of terminal 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 heuris-
       tic 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 multiple 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 patterns/actions.


BUGS
       It was really tempting to name the program "sex" (for either "Smart EXec" or "Send-EXpect"), but good sense (or
       perhaps just Puritanism) prevailed.

       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 me.

       Ultrix  4.1  (at least the latest versions around here) considers timeouts 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 usually irrelevant.  It
       just has to be set to something!  The following probably suffices for most cases.

           set env(TERM) vt100


       Tip (verified only under BSDI BSD/OS 3.1 i386) hangs if SHELL and HOME are not set.  This is  a  problem  under
       cron,  at and in cgi scripts, which do not define these environment variables.  Thus, you must set them explic-
       itly - to what type is usually irrelevant.  It just has to be set to something!  The  following  probably  suf-
       fices for most cases.

           set env(SHELL) /bin/sh
           set env(HOME) /usr/local/bin



       Some  implementations of ptys are designed so that the kernel throws away any unread output after 10 to 15 sec-
       onds (actual number is implementation-dependent) after the process has closed the file descriptor.  Thus Expect
       programs such as

           spawn date
           sleep 20
           expect

       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 interac-
       tive program would be lost due to this behavior.

       On  the  other hand, Cray UNICOS ptys throw away any unread output immediately 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  follow-
       ing example uses both strategies:

           send "speed 9600\r";
           sleep 1
           expect {
               timeout {send "\r"; exp_continue}
               $prompt
           }


       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 discards 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.


EXPECT HINTS
       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 suggestions.

       A common expect problem is how to recognize shell prompts.  Since these are customized differently  by  differ-
       ently  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 describing their prompt (in  particular,  the
       end  of  it) in the environment variable EXPECT_PROMPT.  Code like the following can be used.  If EXPECT_PROMPT
       doesn't exist, the code still has a good chance of functioning correctly.

           set prompt "(%|#|\\$) $"          ;# default prompt
           catch {set prompt $env(EXPECT_PROMPT)}

           expect -re $prompt

       I encourage you to write expect patterns that include the end of whatever you expect to see.  This  avoids  the
       possibility of answering a question before seeing the entire thing.  In addition, while you may well be able to
       answer questions before seeing them entirely, if you 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 pro-
       grams produce output one line at a time.  Assuming this is the case, the * in the pattern of the previous para-
       graph 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 programs 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 translated 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 forgiving in that they will automatically translate newlines to returns, but  most  don't.)   Unfortu-
       nately, there is no way to find out that a program put its terminal into raw mode.

       Rather than manually replacing newlines with returns, the solution is to use the command "stty raw", which will
       stop the translation.  Note, however, that this means that you will no longer get the cooked line-editing  fea-
       tures.

       interact implicitly sets your terminal to raw mode so this problem will not arise then.

       It  is  often  useful  to store passwords (or other private information) in Expect scripts.  This is not recom-
       mended since anything that is stored on a computer is susceptible to being accessed by anyone.  Thus,  interac-
       tively  prompting  for  passwords  from a script is a smarter idea than embedding them literally.  Nonetheless,
       sometimes such embedding is the only possibility.

       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.

SEE ALSO
       Tcl(3), libexpect(3)
       "Exploring Expect: A Tcl-Based Toolkit for Automating  Interactive  Programs"  by  Don  Libes,  pp.  602,  ISBN
       1-56592-090-2, O'Reilly and Associates, 1995.
       "expect: Curing Those Uncontrollable Fits of Interactivity" by Don Libes, Proceedings of the Summer 1990 USENIX
       Conference, Anaheim, California, June 11-15, 1990.
       "Using expect to Automate System Administration Tasks" by Don Libes,  Proceedings  of  the  1990  USENIX  Large
       Installation Systems Administration 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, 1990.
       "expect: Scripts for Controlling Interactive Programs" by Don Libes, Computing Systems, Vol. 4, No. 2,  Univer-
       sity of California Press Journals, 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 Sussex, 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.

AUTHOR
       Don Libes, National Institute of Standards and Technology

ACKNOWLEDGMENTS
       Thanks to John Ousterhout for Tcl, and Scott Paisley for inspiration.  Thanks to Rob Savoye for Expect's  auto-
       configuration code.

       The  HISTORY  file  documents much of the evolution of expect.  It makes interesting reading and might give you
       further insight to this software.  Thanks to the people mentioned in it who sent me bug fixes  and  gave  other
       assistance.

       Design  and implementation of Expect was paid for in part by the U.S. government and is therefore in the public
       domain.  However the author and NIST would like credit if this program and documentation or  portions  of  them
       are used.



                               29 December 1994                      EXPECT(1)