expect(1) — Linux manual page


EXPECT(1)                  General Commands Manual                 EXPECT(1)

NAME         top

       expect - programmed dialogue with interactive programs, Version 5

SYNOPSIS         top

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

INTRODUCTION         top

       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 language 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 control 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

              ·   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

              ·   Carry environment variables, current directory, or any
                  kind of information across rlogin, telnet, tip, su, chgrp,

       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         top

       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

           #!/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 prevent 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 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

       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 (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.

       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 automatically, unless the -n flag is used.  If the
       environment variable DOTDIR is defined, it is treated as a directory
       and .expect.rc is read from there.  (When using Expectk, this option
       is specified as -norc.)  This sourcing 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

       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         top

       Expect uses Tcl (Tool Command Language).  Tcl provides control flow
       (e.g., if, for, break), expression evaluation 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

             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

             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

             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 command 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.

             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

             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
             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 current exit handler is

             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.

             is an alias for send.

             is an alias for send_error.

             is an alias for send_log.

             is an alias for send_tty.

             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 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_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.  Patterns 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

             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 command.  (Such patterns
             are also similar to C-shell regular expressions usually
             referred to as "glob" patterns).  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

             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
             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 characters.  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 forgotten 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 prefixing 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

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

             For example, the following fragment might help a user guide an
             interaction that is already totally automated.  In this case,
             the terminal is put into raw mode.  If the user presses "+", a
             variable is incremented.  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 associated 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

             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_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
             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 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

             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

             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 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
             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 partial 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

             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
             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 \

             If the pattern 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.

             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 process.  If the spawned
             process 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 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 characters 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 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 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 specified 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

             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 -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
             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

                 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
             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 matching 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 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 example, "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
             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 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 minimum 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
             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 running, 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 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 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

             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

             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 interpreted 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 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 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

             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 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
             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
             numerically 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 executed.

             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 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
             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

             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 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

             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 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         top

       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

EXAMPLES         top

       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
       accompanying rationales are still valid and go into a lot more detail
       than this man page.

CAVEATS         top

       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 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 running.
       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 possibly 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 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 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         top

       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 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

       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 explicitly - to what type is usually irrelevant.  It
       just has to be set to something!  The following probably suffices 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 seconds (actual number is
       implementation-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

       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 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
       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         top

       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 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 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

       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
       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.)  Unfortunately, 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 features.

       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 recommended since anything that is
       stored on a computer is susceptible to being accessed by anyone.
       Thus, interactively 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         top

       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,
       "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, University 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         top

       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
       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.

COLOPHON         top

       This page is part of the expect (programmed dialogue with interactive
       programs) project.  Information about the project can be found at 
       ⟨https://core.tcl.tk/expect/index⟩.  If you have a bug report for this
       manual page, see ⟨https://sourceforge.net/p/expect/bugs/⟩.  This page
       was obtained from the tarball expect5.45.3.tar.gz fetched from
       ⟨http://sourceforge.net/projects/expect/files/Expect/⟩ on 2020-08-13.
       If you discover any rendering problems in this HTML version of the
       page, or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the information
       in this COLOPHON (which is not part of the original manual page),
       send a mail to man-pages@man7.org

                              29 December 1994                     EXPECT(1)

Pages that refer to this page: libexpect(3)pty(7)