expect(1) — Linux manual page

NAME | SYNOPSIS | INTRODUCTION | USAGE | COMMANDS | LIBRARIES | PRETTY-PRINTING | EXAMPLES | CAVEATS | BUGS | EXPECT HINTS | SEE ALSO | AUTHOR | ACKNOWLEDGMENTS | COLOPHON

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 criteria.

              •   Connect to another network or BBS (e.g., MCI Mail,
                  CompuServe) and automatically retrieve your mail so
                  that it appears as if it was originally sent to your
                  local system.

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

       There are a variety of reasons why the shell cannot perform these
       tasks.  (Try, you'll see.)  All are possible with Expect.

       In general, Expect is useful for running any program which
       requires interaction between the program and the user.  All that
       is necessary is that the interaction can be characterized
       programmatically.  Expect can also give the user back control
       (without halting the program being controlled) if desired.
       Similarly, the user can return control to the script at any time.

USAGE         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 script:

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

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

       The -c flag prefaces a command to be executed before any in the
       script.  The command should be quoted to 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 -file.)

       By default, the command file is read into memory and executed in
       its entirety.  It is occasionally desirable to read files one
       line at a time.  For example, stdin is read this way.  In order
       to force arbitrary files to be handled this way, use the -b flag.
       (When using Expectk, this option is specified as -buffer.)  Note
       that stdio-buffering may still take place however this shouldn't
       cause problems when reading from a fifo or stdin.

       If the string "-" is supplied as a filename, standard input is
       read instead.  (Use "./-" to read from a file actually named
       "-".)

       The -i flag causes Expect to interactively prompt for commands
       instead of reading them from a file.  Prompting is terminated via
       the exit command or upon EOF.  See interpreter (below) for more
       information.  -i is assumed if neither a command file nor -c is
       used.  (When using Expectk, this option is specified as
       -interactive.)

       -- may be used to delimit the end of the options.  This is useful
       if you want to pass an option-like argument to your script
       without it being interpreted by Expect.  This can usefully be
       placed in the #! line to prevent any flag-like interpretation by
       Expect.  For example, the following will leave the original
       arguments (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
       -version.)

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

       argv0 is defined to be the name of the script (or binary if no
       script is used).  For example, the following prints out the name
       of the script and the first three arguments:

           send_user "$argv0 [lrange $argv 0 2]\n"

COMMANDS         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 spawn_id.

             Both expect and interact will detect when the current
             process exits and implicitly do a close.  But if you kill
             the process by, say, "exec kill $pid", you will need to
             explicitly call close.

             The -onexec flag determines whether the spawn id will be
             closed in any new spawned processes or if the process is
             overlayed.  To leave a spawn id open, use the value 0.  A
             non-zero integer value will force the spawn closed (the
             default) in any new processes.

             The -slave flag closes the slave associated with the spawn
             id.  (See "spawn -pty".)  When the connection is closed,
             the slave is automatically closed as well if still open.

             No matter whether the connection is closed implicitly or
             explicitly, you should call wait to clear up the
             corresponding kernel process slot.  close does not call
             wait since there is no guarantee that closing a process
             connection will cause it to exit.  See wait below for more
             info.

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

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

             With a 1 argument, the debugger is started.  With a 0
             argument, the debugger is stopped.  If a 1 argument is
             preceded by the -now flag, the debugger is started
             immediately (i.e., in the middle of the debug 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.

       disconnect
             disconnects a forked process from the terminal.  It
             continues running in the background.  The process is given
             its own process group (if possible).  Standard I/O is
             redirected to /dev/null.

             The following fragment uses disconnect to continue running
             the script in the background.

                 if {[fork]!=0} exit
                 disconnect
                 . . .

             The following script reads a password, and then runs a
             program every hour that demands a password each time it is
             run.  The script supplies the password so that you only
             have to type it once.  (See the stty command which
             demonstrates how to turn off password echoing.)

                 send_user "password?\ "
                 expect_user -re "(.*)\n"
                 for {} 1 {} {
                     if {[fork]!=0} {sleep 3600;continue}
                     disconnect
                     spawn priv_prog
                     expect Password:
                     send "$expect_out(1,string)\r"
                     . . .
                     exit
                 }

             An advantage to using disconnect over the shell
             asynchronous process feature (&) is that Expect can save
             the terminal parameters prior to disconnection, and then
             later apply them to new ptys.  With &, Expect does not have
             a chance to read the terminal's parameters since the
             terminal is already disconnected by the time Expect
             receives control.

       exit [-opts] [status]
             causes Expect to exit or otherwise prepare to do so.

             The -onexit flag causes the next argument to be used as an
             exit handler.  Without an argument, the current exit
             handler is returned.

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

             Upon exiting, all connections to spawned processes are
             closed.  Closure will be detected as an EOF by spawned
             processes.  exit takes no other actions beyond what the
             normal _exit(2) procedure does.  Thus, spawned processes
             that do not check for EOF may continue to run.  (A variety
             of conditions are important to determining, for example,
             what signals a spawned process will be sent, but these are
             system-dependent, typically documented under exit(3).)
             Spawned processes that continue to run will be inherited by
             init.

             status (or 0 if not specified) is returned as the exit
             status of Expect.  exit is implicitly executed if the end
             of the script is reached.

       exp_continue [-continue_timer]
             The command exp_continue allows expect itself to continue
             executing rather than returning as it normally would. By
             default exp_continue resets the timeout timer. The
             -continue_timer flag prevents timer from being restarted.
             (See expect for more information.)

       exp_internal [-f file] value
             causes further commands to send diagnostic information
             internal to Expect to stderr if value is non-zero.  This
             output is disabled if value is 0.  The diagnostic
             information includes every character received, and every
             attempt made to match the current output against the
             patterns.

             If the optional file is supplied, all normal and debugging
             output is written to that file (regardless of the value of
             value).  Any previous diagnostic output file is closed.

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

       exp_open [args] [-i spawn_id]
             returns a Tcl file identifier that corresponds to the
             original spawn id.  The file identifier can then be used as
             if it were opened by Tcl's open command.  (The spawn id
             should no longer be used.  A wait should not be executed.

             The -leaveopen flag leaves the spawn id open for access
             through Expect commands.  A wait must be executed on the
             spawn id.

       exp_pid [-i spawn_id]
             returns the process id corresponding to the currently
             spawned process.  If the -i flag is used, the pid returned
             corresponds to that of the given spawn id.

       exp_send
             is an alias for send.

       exp_send_error
             is an alias for send_error.

       exp_send_log
             is an alias for send_log.

       exp_send_tty
             is an alias for send_tty.

       exp_send_user
             is an alias for send_user.

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

             With no arguments, the current version of Expect is
             returned.  This version may then be encoded in your script.
             If you actually know that you are not using features of
             recent versions, you can specify an 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 braces.

             If a pattern is the keyword eof, the corresponding body is
             executed upon end-of-file.  If a pattern is the keyword
             timeout, the corresponding body is executed upon timeout.
             If no timeout keyword is used, an implicit null action is
             executed upon timeout.  The default timeout period is 10
             seconds but may be set, for example to 30, by the command
             "set timeout 30".  An infinite timeout may be designated by
             the value -1.  If a pattern is the keyword default, the
             corresponding body is executed upon either timeout or end-
             of-file.

             If a pattern matches, then the corresponding body is
             executed.  expect returns the result of the body (or the
             empty string if no pattern matched).  In the event that
             multiple patterns match, the one appearing first is used to
             select a body.

             Each time new output arrives, it is compared to each
             pattern in the order they are listed.  Thus, you may test
             for absence of a match by making the last pattern something
             guaranteed to appear, such as a prompt.  In situations
             where there is no prompt, you must use timeout (just like
             you would if you were interacting manually).

             Patterns are specified in three ways.  By default, patterns
             are specified as with Tcl's string match 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
                     connected
                 }

             Quotes are necessary on the fourth pattern since it
             contains a space, which would otherwise separate the
             pattern from the action.  Patterns with the same action
             (such as the 3rd and 4th) require listing the actions
             again.  This can be avoid by using regexp-style patterns
             (see below).  More information on 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
                     connected
                 }

             Both types of patterns are "unanchored".  This means that
             patterns do not have to match the entire string, but can
             begin and end the match anywhere in the string (as long as
             everything else matches).  Use ^ to match the beginning of
             a string, and $ to match the end.  Note that if you do not
             wait for the end of a string, your responses can easily end
             up in the middle of the string as they are echoed from the
             spawned process.  While still producing correct results,
             the output can look unnatural.  Thus, use of $ is
             encouraged if you can exactly describe the characters at
             the end of a string.

             Note that in many editors, the ^ and $ match the beginning
             and end of lines respectively. However, because expect is
             not line oriented, these characters match the beginning and
             end of the data (as opposed to lines) currently in the
             expect matching buffer.  (Also, see the note below on
             "system indigestion.")

             The -ex flag causes the pattern to be matched as an "exact"
             string.  No interpretation of *, ^, etc is made (although
             the usual Tcl conventions must still be observed).  Exact
             patterns are always unanchored.

             The -nocase flag causes uppercase characters of the output
             to compare as if they were lowercase 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
                     connected
                 }

             The value of the global variable any_spawn_id may be used
             to match patterns to any spawn_ids that are named with all
             other -i flags in the current expect command.  The spawn_id
             from a -i flag with no 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
                         exp_continue
                     } incorrect {
                         send_user "invalid password or account\n"
                         exit
                     } timeout {
                         send_user "connection to $host timed out\n"
                         exit
                     } eof {
                         send_user \
                             "connection to host failed: $expect_out(buffer)"
                         exit
                     } -re $prompt
                 }

             For example, the following fragment might help a user guide
             an interaction that is already totally 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 patterns.

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

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

                 expect_before -info -i $proc

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

             Instead of a spawn id specification, the flag "-all" will
             cause "-info" to report on all spawn ids.

             The output of the -info flag can be reused as the argument
             to expect_before.

       expect_tty [expect_args]
             is like expect but it reads characters from /dev/tty (i.e.
             keystrokes from the user).  By default, 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 missing.

             If the arguments to the entire interact statement require
             more than one line, all the arguments may be "braced" into
             one so as to avoid terminating each line with a backslash.
             In this one case, the usual Tcl substitutions will occur
             despite the braces.

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

                 set CTRLZ \032
                 interact {
                     -reset $CTRLZ {exec kill -STOP [pid]}
                     \001   {send_user "you typed a control-A\n";
                             send "\001"
                            }
                     $      {send_user "The date is [clock format [clock seconds]]."}
                     \003   exit
                     foo    {send_user "bar"}
                     ~~
                 }

             In string-body pairs, strings are matched in the order they
             are listed as arguments.  Strings that 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 options.)

             The -re flag forces the string to be interpreted as a
             regexp-style pattern.  In this case, matching substrings
             are stored in the variable interact_out similarly to the
             way expect stores its output in the variable expect_out.
             The -indices flag is similarly supported.

             The pattern eof introduces an action that is executed upon
             end-of-file.  A separate eof pattern may also follow the
             -output flag in which case it is matched if an eof is
             detected while writing output.  The default eof action is
             "return", so that interact simply returns upon any EOF.

             The pattern timeout introduces a timeout (in seconds) and
             action that is executed after no characters have been read
             for a given time.  The timeout pattern applies to the most
             recently specified process.  There is no default timeout.
             The special variable "timeout" (used by the expect command)
             has no affect on this timeout.

             For example, the following statement could be used to
             autologout users who have not typed anything for an hour
             but who still get frequent system messages:

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

             If the pattern is the keyword null, and nulls are allowed
             (via the remove_nulls command), the 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 commands.

             By default, the prompt contains two integers.  The first
             integer describes the depth of the evaluation stack (i.e.,
             how many times Tcl_Eval has been called).  The second
             integer is the Tcl history identifier.  The prompt can be
             set by defining a procedure called "prompt1" whose return
             value becomes the next prompt.  If a statement has open
             quotes, parens, braces, or brackets, a secondary prompt (by
             default "+> ") is issued upon newline.  The secondary
             prompt may be set by defining a procedure called "prompt2".

             During interpreter, cooked mode is used, even if the its
             caller was using raw mode.

             If stdin is closed, interpreter will return unless the -eof
             flag is used, in which case the subsequent argument is
             invoked.

       log_file [args] [[-a] file]
             If a filename is provided, log_file will record a
             transcript of the session (beginning at that point) in the
             file.  log_file will stop recording if no argument is
             given.  Any previous log file is closed.

             Instead of a filename, a Tcl file identifier may be
             provided by using the -open or -leaveopen flags.  This is
             similar to the spawn command.  (See spawn for more info.)

             The -a flag forces output to be logged that was suppressed
             by the log_user command.

             By default, the log_file command appends to old files
             rather than truncating them, for the convenience of being
             able to turn logging off and on multiple times in one
             session.  To truncate files, use the -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 master.

                 overlay -0 $spawn_id -1 $spawn_id -2 $spawn_id chess

             This is more efficient than "interact -u", however, it
             sacrifices the ability to do programmed interaction since
             the Expect process is no longer in control.

             Note that no controlling terminal is provided.  Thus, if
             you 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 identifiers.

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

             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 -slave".

             The -ignore flag names a signal to be ignored in the
             spawned process.  Otherwise, signals get the default
             behavior.  Signals are named as in the trap command, except
             that each signal requires a separate flag.

       strace level
             causes following statements to be printed before being
             executed.  (Tcl's trace command traces variables.)  level
             indicates how far down in the call stack to trace.  For
             example, the following command runs Expect while tracing
             the first 4 levels of calls, but none below that.

                 expect -c "strace 4" script.exp

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

       stty args
             changes terminal modes similarly to the external stty
             command.

             By default, the controlling terminal is accessed.  Other
             terminals can be accessed by appending "< /dev/tty..." to
             the command.  (Note that the arguments should not be
             grouped into a single argument.)

             Requests for status return it as the result of the command.
             If no status is requested and the 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 signal.

             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 set.

             Additional elements may appear at the end of the return
             value from wait.  An optional fifth element identifies a
             class of information.  Currently, the only possible value
             for this element is CHILDKILLED in which case the next two
             values are the C-style 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.

PRETTY-PRINTING         top

       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) prevailed.

       On some systems, when a shell is spawned, it complains about not
       being able to access the tty but runs anyway.  This means your
       system has a mechanism for gaining the controlling tty that
       Expect doesn't know about.  Please find out what it is, and send
       this information back to me.

       Ultrix 4.1 (at least the latest versions around here) considers
       timeouts of above 1000000 to be equivalent to 0.

       Digital UNIX 4.0A (and probably other versions) refuses to
       allocate ptys if you define a SIGCHLD handler.  See grantpt page
       for more info.

       IRIX 6.0 does not handle pty permissions correctly so that if
       Expect attempts to allocate a pty previously used by someone
       else, it fails.  Upgrade to IRIX 6.1.

       Telnet (verified only under SunOS 4.1.2) hangs if TERM is not
       set.  This is a problem under cron, at and in cgi scripts, which
       do not define TERM.  Thus, you must set it explicitly - to what
       type is usually irrelevant.  It just has to be set to something!
       The following probably suffices for most cases.

           set env(TERM) vt100

       Tip (verified only under BSDI BSD/OS 3.1 i386) hangs if SHELL and
       HOME are not set.  This is a problem under cron, at and in cgi
       scripts, which do not define these environment variables.  Thus,
       you must set them 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
           expect

       will fail.  To avoid this, invoke non-interactive programs with
       exec rather than spawn.  While such situations are conceivable,
       in practice I have never encountered a situation in which the
       final output of a truly interactive program would be lost due to
       this behavior.

       On the other hand, Cray UNICOS ptys throw away any unread output
       immediately after the process has closed the file descriptor.  I
       have reported this to Cray and they are working on a fix.

       Sometimes a delay is required between a prompt and a response,
       such as when a tty interface is changing UART settings or
       matching baud rates by looking for start/stop bits.  Usually, all
       this is require is to sleep for a second or two.  A more robust
       technique is to retry until the hardware is ready to receive
       input.  The following example uses both strategies:

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

       trap -code will not work with any command that sits in Tcl's
       event loop, such as sleep.  The problem is that in the event
       loop, Tcl discards the return codes from async event handlers.  A
       workaround is to set a flag in the trap code.  Then check the
       flag immediately after the command (i.e., sleep).

       The expect_background command ignores -timeout arguments and has
       no concept of timeouts in general.

EXPECT HINTS         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
       explicitly.

       If you use a pattern of the form X*, the * will match all the
       output received from the end of X to the last thing received.
       This sounds intuitive but can be somewhat confusing because the
       phrase "last thing received" can vary depending upon the speed of
       the computer and the processing of I/O both by the kernel and the
       device driver.

       In particular, humans tend to see program output arriving in huge
       chunks (atomically) when in reality most programs produce output
       one line at a time.  Assuming this is the case, the * in the
       pattern of the previous paragraph may only match the end of the
       current line even though there seems to be more, because at the
       time of the match that was all the output that had been received.

       expect has no way of knowing that further output is coming unless
       your pattern specifically accounts for it.

       Even depending on line-oriented buffering is unwise.  Not only do
       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, 1990.
       "Tcl: An Embeddable Command Language" by John Ousterhout,
       Proceedings of the Winter 1990 USENIX Conference, Washington,
       D.C., January 22-26, 1990.
       "expect: Scripts for Controlling Interactive Programs" by Don
       Libes, Computing Systems, Vol. 4, No. 2, 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

ACKNOWLEDGMENTS         top

       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
       2020-12-18.  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)