expect Man page

EXPECT(1) General Commands Manual EXPECT(1)


expect – programmed dialogue with interactive programs, Version 5


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

Expect is a program that “talks” to other interactive programs accord‐
ing to a script. Following the script, Expect knows what can be
expected from a program and what the correct response should be. An
interpreted language provides branching and high-level control struc‐
tures to direct the dialogue. In addition, the user can take control
and interact directly when desired, afterward returning control to the

Expectk is a mixture of Expect and Tk. It behaves just like Expect and
Tk’s wish. Expect can also be used directly in C or C++ (that is,
without Tcl). See libexpect.

The name “Expect” comes from the idea of send/expect sequences popular‐
ized by uucp, kermit and other modem control programs. However unlike
uucp, Expect is generalized so that it can be run as a user-level com‐
mand with any program and task in mind. Expect can actually talk to
several programs at the same time.

For example, here are some things Expect can do:

· Cause your computer to dial you back, so that you can login
without paying for the call.

· Start a game (e.g., rogue) and if the optimal configuration
doesn’t appear, restart it (again and again) until it does,
then hand over control to you.

· Run fsck, and in response to its questions, answer “yes”,
“no” or give control back to you, based on predetermined

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

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

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

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

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

#!/usr/bin/expect -f

Of course, the path must accurately describe where Expect lives.
/usr/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 exe‐
cuted with a single -c by separating them with semicolons. Commands
are executed in the order they appear. (When using Expectk, this
option is specified as -command.)

The -d flag enables some diagnostic output, which primarily reports
internal activity of commands such as expect and interact. This flag
has the same effect as “exp_internal 1” at the beginning of an Expect
script, plus the version of Expect is printed. (The strace command is
useful for tracing statements, and the trace command is useful for
tracing variable assignments.) (When using Expectk, this option is
specified as -diag.)

The -D flag enables an interactive debugger. An integer value should
follow. The debugger will take control before the next Tcl procedure
if the value is non-zero or if a ^C is pressed (or a breakpoint is hit,
or other appropriate debugger command appears in the script). See the
README file or SEE ALSO (below) for more information on the debugger.
(When using Expectk, this option is specified as -Debug.)

The -f flag prefaces a file from which to read commands from. The flag
itself is optional as it is only useful when using the #! notation (see
above), so that other arguments may be supplied on the command line.
(When using Expectk, this option is specified as -file.)

By default, the command file is read into memory and executed in its
entirety. It is occasionally desirable to read files one line at a
time. For example, stdin is read this way. In order to force arbi‐
trary files to be handled this way, use the -b flag. (When using
Expectk, this option is specified as -buffer.)Notethatstdio-buffering‐
maystilltakeplacehoweverthis shouldn’t cause problems when reading from
a fifo or stdin.

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

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

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

#!/usr/bin/expect —

Note that the usual getopt 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 speci‐
fied 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 corre‐
sponding 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”

Expect uses Tcl (Tool Command Language). Tcl provides control flow
(e.g., if, for, break), expression evaluation and several other fea‐
tures such as recursion, procedure definition, etc. Commands used here
but not defined (e.g., set, if, exec) are Tcl commands (see tcl(3)).
Expect supports additional commands, described below. Unless otherwise
specified, commands return the empty string.

Commands are listed alphabetically so that they can be quickly located.
However, new users may find it easier to start by reading the descrip‐
tions of spawn, send, expect, and interact, in that order.

Note that the best introduction to the language (both Expect and Tcl)
is provided in the book “Exploring Expect” (see SEE ALSO below). Exam‐
ples are included in this man page but they are very limited since this
man page is meant primarily as reference material.

Note that in the text of this man page, “Expect” with an uppercase “E”
refers to the Expect program while “expect” with a lower-case “e”
refers to the expect command within the Expect program.)

close [-slave] [-onexec 0|1] [-i spawn_id] closes the connection to the current process. Most interactive
programs will detect EOF on their stdin and exit; thus close usu‐
ally suffices to kill the process as well. The -i flag declares
the process to close corresponding to the named spawn_id.

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

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

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

No matter whether the connection is closed implicitly or explic‐
itly, you should call wait to clear up the corresponding kernel
process slot. close does not call wait since there is no guaran‐
tee that closing a process connection will cause it to exit. See
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 run‐
ning, otherwise a 0 is returned.

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

The debug command does not change any traps. Compare this to
starting Expect with the -D flag (see above).

See the README file or SEE ALSO (below) for more information on
the debugger.

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

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

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

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

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

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

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

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

The -noexit flag causes Expect to prepare to exit but stop short
of actually returning control to the operating system. The user-
defined exit handler is run as well as Expect’s own internal han‐
dlers. 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 con‐
tinue to run. (A variety of conditions are important to deter‐
mining, for example, what signals a spawned process will be sent,
but these are system-dependent, typically documented under
exit(3).) Spawned processes that continue to run will be inher‐
ited by init.

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

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

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

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

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

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

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

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

is an alias for send.

is an alias for send_error.

is an alias for send_log.

is an alias for send_tty.

is an alias for send_user.

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

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

Versions consist of three numbers separated by dots. First is
the major number. Scripts written for versions of Expect with a
different major number will almost certainly not work. exp_ver‐
sion returns an error if the major numbers do not match.

Second is the minor number. Scripts written for a version with a
greater minor number than the current version may depend upon
some new feature and might not run. exp_version returns an error
if the major numbers match, but the script minor number is
greater than that of the running Expect.

Third is a number that plays no part in the version comparison.
However, it is incremented when the Expect software distribution
is changed in any way, such as by additional documentation or
optimization. It is reset to 0 upon each new minor version.

With the -exit flag, Expect prints an error and exits if the ver‐
sion is out of date.

expect [[-opts] pat1 body1] … [-opts] patn [bodyn] waits until one of the patterns matches the output of a spawned
process, a specified time period has passed, or an end-of-file is
seen. If the final body is empty, it may be omitted.

Patterns from the most recent expect_before command are implic‐
itly used before any other patterns. Patterns from the most
recent expect_after command are implicitly used after any other

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

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

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

Each time new output arrives, it is compared to each pattern in
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

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

For example, the following fragment looks for a successful login.
(Note that abort is presumed to be a procedure defined elsewhere
in the script.)

expect {
busy {puts busy\n ; exp_continue}
failed abort
“invalid password” abort
timeout abort

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

Regexp-style patterns follow the syntax defined by Tcl’s regexp
(short for “regular expression”) command. regexp patterns are
introduced with the flag -re. The previous example can be
rewritten using a regexp as:

expect {
busy {puts busy\n ; exp_continue}
-re “failed|invalid password” abort
timeout abort

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

Note that in many editors, the ^ and $ match the beginning and
end of lines respectively. However, because expect is not line
oriented, these characters match the beginning and end of the
data (as opposed to lines) currently in the expect matching buf‐
fer. (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

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 key‐
word is used, the forgotten characters are written to

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

Upon matching a pattern (or eof or full_buffer), any matching and
previously unmatched output is saved in the variable
expect_out(buffer). Up to 9 regexp substring matches are saved
in the variables expect_out(1,string) through
expect_out(9,string). If the -indices flag is used before a pat‐
tern, the starting and ending indices (in a form suitable for
lrange) of the 10 strings are stored in the variables
expect_out(X,start) and expect_out(X,end) where X is a digit,
corresponds to the substring position in the buffer. 0 refers to
strings which matched the entire pattern and is generated for
glob patterns as well as regexp patterns. For example, if a
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 out‐
put from the process.

Normally, the matched output is discarded from Expect’s internal
buffers. This may be prevented by prefixing a pattern with the
-notransfer flag. This flag is especially useful in experiment‐
ing (and can be abbreviated to “-not” for convenience while

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

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

By default, patterns are matched against output from the current
process, however the -i flag declares the output from the named
spawn_id list be matched against any following patterns (up to
the next -i). The spawn_id list should either be a whitespace
separated list of spawn_ids or a variable referring to such a
list of spawn_ids.

For example, the following example waits for “connected” from the
current process, or “busy”, “failed” or “invalid password” from
the spawn_id named by $proc2.

expect {
-i $proc2 busy {puts busy\n ; exp_continue}
-re “failed|invalid password” abort
timeout abort

The value of the global variable any_spawn_id may be used to
match patterns to any spawn_ids that are named with all other -i
flags in the current expect command. The spawn_id from a -i flag
with no associated pattern (i.e., followed immediately by another
-i) is made available to any other patterns in the same expect
command associated with any_spawn_id.

The -i flag may also name a global variable in which case the
variable is read for a list of spawn ids. The variable is reread
whenever it changes. This provides a way of changing the I/O
source while the command is in execution. Spawn ids provided
this way are called “indirect” spawn ids.

Actions such as break and continue cause control structures
(i.e., for, proc) to behave in the usual way. The command
exp_continue allows expect itself to continue executing rather
than returning as it normally would.

This is useful for avoiding explicit loops or repeated expect
statements. The following example is part of a fragment to auto‐
mate rlogin. The exp_continue avoids having to write a second
expect statement (to look for the prompt again) if the rlogin
prompts for a password.

expect {
Password: {
stty -echo
send_user “password (for $user) on $host: ”
expect_user -re “(.*)\n”
send_user “\n”
send “$expect_out(1,string)\r”
stty echo
} incorrect {
send_user “invalid password or account\n”
} timeout {
send_user “connection to $host timed out\n”
} eof {
send_user \
“connection to host failed: $expect_out(buffer)”
} -re $prompt

For example, the following fragment might help a user guide an
interaction that is already totally automated. In this case, the
terminal is put into raw mode. If the user presses “+”, a vari‐
able 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 cur‐
rent expect to continue pattern matching after executing the cur‐
rent action.

stty raw -echo
expect_after {
-i $user_spawn_id
“p” {send “\r\r\r”; exp_continue}
“+” {incr foo; exp_continue}
“i” {interact; exp_continue}
“quit” exit

By default, exp_continue resets the timeout timer. The timer is
not restarted, if exp_continue is called with the -continue_timer

expect_after [expect_args] works identically to the expect_before except that if patterns
from both expect and expect_after can match, the expect pattern
is used. See the expect_before command for more information.

expect_background [expect_args] takes the same arguments as expect, however it returns immedi‐
ately. Patterns are tested whenever new input arrives. The pat‐
tern timeout and default are meaningless to expect_background and
are silently discarded. Otherwise, the expect_background command
uses expect_before and expect_after patterns just like expect

When expect_background actions are being evaluated, background
processing for the same spawn id is blocked. Background process‐
ing is unblocked when the action completes. While background
processing is blocked, it is possible to do a (foreground) expect
on the same spawn id.

It is not possible to execute an expect while an expect_back‐
ground is unblocked. expect_background for a particular spawn id
is deleted by declaring a new expect_background with the same
spawn id. Declaring expect_background with no pattern removes
the given spawn id from the ability to match patterns in the

expect_before [expect_args] takes the same arguments as expect, however it returns immedi‐
ately. Pattern-action pairs from the most recent expect_before
with the same spawn id are implicitly added to any following
expect commands. If a pattern matches, it is treated as if it
had been specified in the expect command itself, and the associ‐
ated body is executed in the context of the expect command. If
patterns from both expect_before and expect can match, the
expect_before pattern is used.

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

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

The -info flag causes expect_before to return the current speci‐
fications 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 -indi‐
rect suppresses direct spawn ids that come only from indirect

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

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

expect_tty [expect_args] is like expect but it reads characters from /dev/tty (i.e. key‐
strokes 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. key‐
strokes from the user). By default, reading is performed in
cooked mode. Thus, lines must end with a return in order for
expect to see them. This may be changed via stty (see the stty
command below).

fork creates a new process. The new process is an exact copy of the
current Expect process. On success, fork returns 0 to the new
(child) process and returns the process ID of the child process
to the parent process. On failure (invariably due to lack of
resources, e.g., swap space, memory), fork returns -1 to the par‐
ent process, and no child process is created.

Forked processes exit via the exit command, just like the origi‐
nal process. Forked processes are allowed to write to the log
files. If you do not disable debugging or logging in most of the
processes, the result can be confusing.

Some pty implementations may be confused by multiple readers and
writers, even momentarily. Thus, it is safest to fork before
spawning processes.

interact [string1 body1] … [stringn [bodyn]] gives control of the current process to the user, so that key‐
strokes 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 follow‐
ing 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

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

In string-body pairs, strings are matched in the order they are
listed as arguments. Strings that partially match are not sent
to the current process in anticipation of the remainder coming.
If characters are then entered such that there can no longer pos‐
sibly be a match, only the part of the string will be sent to the
process that cannot possibly begin another match. Thus, strings
that are substrings of partial matches can match later, if the
original strings that was attempting to be match ultimately

By default, string matching is exact with no wild cards. (In
contrast, the expect command uses glob-style patterns by
default.) The -ex flag may be used to protect patterns that
might otherwise match interact flags from doing so. Any pattern
beginning with a “-” should be protected this way. (All
strings starting with “-” are reserved for future options.)

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

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

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

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

interact -input $user_spawn_id timeout 3600 return -output \

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

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

Actions such as break and continue cause control structures
(i.e., for, proc) to behave in the usual way. However return
causes interact to return to its caller, while inter_return
causes interact to cause a return in its caller. For example, if
“proc foo” called interact which then executed the action
inter_return, proc foo would return. (This means that if inter‐
act calls interpreter interactively typing return will cause the
interact to continue, while inter_return will cause the interact
to return to its caller.)

During interact, raw mode is used so that all characters may be
passed to the current process. If the current process does not
catch job control signals, it will stop if sent a stop signal (by
default ^Z). To restart it, send a continue signal (such as by
“kill -CONT “). If you really want to send a SIGSTOP to
such a process (by ^Z), consider spawning csh first and then run‐
ning your program. On the other hand, if you want to send a
SIGSTOP to Expect itself, first call interpreter (perhaps by
using an escape character), and then press ^Z.

String-body pairs can be used as a shorthand for avoiding having
to enter the interpreter and execute commands interactively. The
previous terminal mode is used while the body of a string-body
pair is being executed.

For speed, actions execute in raw mode by default. The -reset
flag resets the terminal to the mode it had before interact was
executed (invariably, cooked mode). Note that characters entered
when the mode is being switched may be lost (an unfortunate fea‐
ture of the terminal driver on some systems). The only reason to
use -reset is if your action depends on running in cooked mode.

The -echo flag sends characters that match the following pattern
back to the process that generated them as each character is
read. This may be useful when the user needs to see feedback
from partially typed patterns.

If a pattern is being echoed but eventually fails to match, the
characters are sent to the spawned process. If the spawned
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 fol‐
lowing excerpt is from rftp, the recursive-ftp script, where the
user is prompted to enter ~g, ~p, or ~l, to get, put, or list the
current directory recursively. These are so far away from the
normal ftp commands, that the user is unlikely to type ~ followed
by anything else, except mistakenly, in which case, they’ll prob‐
ably just ignore the result anyway.

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

The -nobuffer flag sends characters that match the following pat‐
tern on to the output process as characters are read.

This is useful when you wish to let a program echo back the pat‐
tern. 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 partic‐
ular, interact will force its output to be logged (sent to the
standard output) since it is presumed the user doesn’t wish to
interact blindly.

The -o flag causes any following key-body pairs to be applied to
the output of the current process. This can be useful, for exam‐
ple, when dealing with hosts that send unwanted characters during
a telnet session.

By default, interact expects the user to be writing stdin and
reading stdout of the Expect process itself. The -u flag (for
“user”) makes interact look for the user as the process named by
its argument (which must be a spawned id).

This allows two unrelated processes to be joined together without
using an explicit loop. To aid in debugging, Expect diagnostics
always go to stderr (or stdout for certain logging and debugging
information). For the same reason, the interpreter command will
read interactively from stdin.

For example, the following fragment creates a login process.
Then it dials the user (not shown), and finally connects the two
together. Of course, any process may be substituted for login.
A shell, for example, would allow the user to work without sup‐
plying an account and password.

spawn login
set login $spawn_id
spawn tip modem
# dial back out to user
# connect user to login
interact -u $login

To send output to multiple processes, list each spawn id list
prefaced by a -output flag. Input for a group of output spawn
ids may be determined by a spawn id list prefaced by a -input
flag. (Both -input and -output may take lists in the same form
as the -i flag in the expect command, except that any_spawn_id is
not meaningful in interact.) All following flags and strings (or
patterns) apply to this input until another -input flag appears.
If no -input appears, -output implies “-input $user_spawn_id
-output”. (Similarly, with patterns that do not have -input.)
If one -input is specified, it overrides $user_spawn_id. If a
second -input is specified, it overrides $spawn_id. Additional
-input flags may be specified.

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 sec‐
ondary prompt (by default “+> “) is issued upon newline. The
secondary prompt may be set by defining a procedure called

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

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

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

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

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

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

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

log_user -info|0|1
By default, the send/expect dialogue is logged to stdout (and a
logfile if open). The logging to stdout is disabled by the com‐
mand “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 dis‐
connect or remap standard input, programs that do job control
(shells, login, etc) will not function properly.

parity [-d] [-i spawn_id] [value] defines whether parity should be retained or stripped from the
output of spawned processes. If value is zero, parity is
stripped, otherwise it is not stripped. With no value argument,
the current value is returned.

With the -d flag, the default parity value is set. (The initial
default is 1, i.e., parity is not stripped.) With the -i flag,
the parity value is set for the named spawn id, otherwise it is
set for the current process.

remove_nulls [-d] [-i spawn_id] [value] defines whether nulls are retained or removed from the output of
spawned processes before pattern matching or storing in the vari‐
able expect_out or interact_out. If value is 1, nulls are
removed. If value is 0, nulls are not removed. With no value
argument, the current value is returned.

With the -d flag, the default value is set. (The initial default
is 1, i.e., nulls are removed.) With the -i flag, the value is
set for the named spawn id, otherwise it is set for the current

Whether or not nulls are removed, Expect will record null bytes
to the log and stdout.

send [-flags] string
Sends string to the current process. For example, the command

send “hello world\r”

sends the characters, h e l l o w o r l d 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 char‐
acter 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-new‐
line sequences so that they appear as if the terminal was in
cooked mode. The -raw flag disables this translation.

The -null flag sends null characters (0 bytes). By default, one
null is sent. An integer may follow the -null to indicate how
many nulls to send.

The -break flag generates a break condition. This only makes
sense if the spawn id refers to a tty device opened via “spawn
-open”. If you have spawned a process such as tip, you should
use tip’s convention for generating a break.

The -s flag forces output to be sent “slowly”, thus avoid the
common situation where a computer outtypes an input buffer that
was designed for a human who would never outtype the same buffer.
This output is controlled by the value of the variable
“send_slow” which takes a two element list. The first element is
an integer that describes the number of bytes to send atomically.
The second element is a real number that describes the number of
seconds by which the atomic sends must be separated. For exam‐
ple, “set send_slow {10 .001}” would force “send -s” to send
strings with 1 millisecond in between each 10 characters sent.

The -h flag forces output to be sent (somewhat) like a human
actually typing. Human-like delays appear between the charac‐
ters. (The algorithm is based upon a Weibull distribution, with
modifications to suit this particular application.) This output
is controlled by the value of the variable “send_human” which
takes a five element list. The first two elements are average
interarrival time of characters in seconds. The first is used by
default. The second is used at word endings, to simulate the
subtle pauses that occasionally occur at such transitions. The
third parameter is a measure of variability where .1 is quite
variable, 1 is reasonably variable, and 10 is quite invariable.
The extremes are 0 to infinity. The last two parameters are,
respectively, a minimum and maximum interarrival time. The mini‐
mum and maximum are used last and “clip” the final time. The
ultimate average can be quite different from the given average if
the minimum and maximum clip enough values.

As an example, the following command emulates a fast and consis‐
tent typist:

set send_human {.1 .3 1 .05 2}
send -h “I’m hungry. Let’s do lunch.”

while the following might be more suitable after a hangover:

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 correc‐
tions 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 ini‐
tial prompt, you can precede send by a delay as in:

# To avoid giving hackers hints on how to break in,
# this system does not prompt for an external password.
# Wait for 5 seconds for exec to complete
spawn telnet 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

send_tty [-flags] string
is like send, except that the output is sent to /dev/tty rather
than the current process.

send_user [-flags] string
is like send, except that the output is sent to stdout rather
than the current process.

sleep seconds
causes the script to sleep for the given number of seconds. Sec‐
onds may be a decimal number. Interrupts (and Tk events if you
are using Expectk) are processed while Expect sleeps.

spawn [args] program [args] creates a new process running program args. Its stdin, stdout
and stderr are connected to Expect, so that they may be read and
written by other Expect commands. The connection is broken by
close or if the process itself closes any of the file identi‐

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

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). If the variable stty_init is
defined, it is interpreted in the style of stty arguments as fur‐
ther configuration. For example, “set stty_init raw” will cause
further spawned processes’s terminals to start in raw mode.
-nottycopy skips the initialization based on the user’s tty.
-nottyinit skips the “sane” initialization.

Normally, spawn takes little time to execute. If you notice
spawn taking a significant amount of time, it is probably encoun‐
tering ptys that are wedged. A number of tests are run on ptys
to avoid entanglements with errant processes. (These take 10
seconds per wedged pty.) Running Expect with the -d option will
show if Expect is encountering many ptys in odd states. If you
cannot kill the processes to which these ptys are attached, your
only recourse may be to reboot.

If program cannot be spawned successfully because exec(2) fails
(e.g. when program doesn’t exist), an error message will be
returned by the next interact or expect command as if program had
run and produced the error message as output. This behavior is a
natural consequence of the implementation of spawn. Internally,
spawn forks, after which the spawned process has no way to commu‐
nicate with the original Expect process except by communication
via the spawn_id.

The -open flag causes the next argument to be interpreted as a
Tcl file identifier (i.e., returned by open.) The spawn id can
then be used as if it were a spawned process. (The file identi‐
fier should no longer be used.) This lets you treat raw devices,
files, and pipelines as spawned processes without using a pty. 0
is returned to indicate there is no associated process. When the
connection to the spawned process is closed, so is the Tcl file
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 cor‐
responding to the pty slave. It can be closed using “close

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

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

expect -c “strace 4” script.exp

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

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

By default, the controlling terminal is accessed. Other termi‐
nals can be accessed by appending “< /dev/tty..." to the command. (Note that the arguments should not be grouped into a single 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 as input, just as if it had been typed as a
command from a terminal. Expect waits until the shell termi‐
nates. The return status from sh is handled the same way that
exec handles its return status.

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 cur‐
rent time is used.

The -gmt flag forces timestamp output to use the GMT timezone.
With no flag, the local timezone is used.

trap [[command] signals] causes the given command to be executed upon future receipt of
any of the given signals. The command is executed in the global
scope. If command is absent, the signal action is returned. If
command is the string SIG_IGN, the signals are ignored. If com‐
mand is the string SIG_DFL, the signals are result to the system
default. signals is either a single signal or a list of signals.
Signals may be specified numerically or symbolically as per sig‐
nal(3). The “SIG” prefix may be omitted.

With no arguments (or the argument -number), trap returns the
signal number of the trap command currently being executed.

The -code flag uses the return code of the command in place of
whatever code Tcl was about to return when the command originally
started running.

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 sig‐
nal 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 follow‐
ing trap, created by default when Expect starts.

trap exit {SIGINT SIGTERM}

If you use the -D flag to start the debugger, SIGINT is redefined
to start the interactive debugger. This is due to the following

trap {exp_debug 1} SIGINT

The debugger trap can be changed by setting the environment vari‐
able EXPECT_DEBUG_INIT to a new trap command.

You can, of course, override both of these just by adding trap
commands to your script. In particular, if you have your own
“trap exit SIGINT”, this will override the debugger trap. This
is useful if you want to prevent users from getting to the debug‐
ger at all.

If you want to define your own trap on SIGINT but still trap to
the debugger when it is running, use:

if {![exp_debug]} {trap mystuff SIGINT}

Alternatively, you can trap to the debugger using some other sig‐

trap will not let you override the action for SIGALRM as this is
used internally to Expect. The disconnect command sets SIGALRM
to SIG_IGN (ignore). You can reenable this as long as you dis‐
able it during subsequent spawn commands.

See signal(3) for more info.

wait [args] delays until a spawned process (or the current process if none is
named) terminates.

wait normally returns a list of four integers. The first integer
is the pid of the process that was waited upon. The second inte‐
ger is the corresponding spawn id. The third integer is -1 if an
operating system error occurred, or 0 otherwise. If the third
integer was 0, the fourth integer is the status returned by the
spawned process. If the third integer was -1, the fourth integer
is the value of errno set by the operating system. The global
variable errorCode is also set.

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

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.

Expect automatically knows about two built-in libraries for Expect
scripts. These are defined by the directories named in the variables
exp_library and exp_exec_library. Both are meant to contain utility
files that can be used by other scripts.

exp_library contains architecture-independent files. exp_exec_library
contains architecture-dependent files. Depending on your system, both
directories may be totally empty. The existence of the file
$exp_exec_library/cat-buffers describes whether your /bin/cat buffers
by default.

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

vgrind -lexpect file

It many not be apparent how to put everything together that the man
page describes. I encourage you to read and try out the examples in
the example directory of the Expect distribution. Some of them are
real programs. Others are simply illustrative of certain techniques,
and of course, a couple are just quick hacks. The INSTALL file has a
quick overview of these programs.

The Expect papers (see SEE ALSO) are also useful. While some papers
use syntax corresponding to earlier versions of Expect, the accompany‐
ing rationales are still valid and go into a lot more detail than this
man page.

Extensions may collide with Expect’s command names. For example, send
is defined by Tk for an entirely different purpose. For this reason,
most of the Expect commands are also available as “exp_XXXX”. Commands
and variables beginning with “exp”, “inter”, “spawn”, and “timeout” do
not have aliases. Use the extended command names if you need this com‐
patibility between environments.

Expect takes a rather liberal view of scoping. In particular, vari‐
ables read by commands specific to the Expect program will be sought
first from the local scope, and if not found, in the global scope. For
example, this obviates the need to place “global timeout” in every pro‐
cedure you write that uses expect. On the other hand, variables writ‐
ten are always in the local scope (unless a “global” command has been
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 equiva‐
lent), 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 termi‐
nal parameters, but you must then be very careful when writing scripts
for such environments. In the case of emacs, avoid depending upon
things like echoing and end-of-line mappings.

The commands that accepted arguments braced into a single list (the
expect variants and interact) use a heuristic to decide if the list is
actually one argument or many. The heuristic can fail only in the case
when the list actually does represent a single argument which has mul‐
tiple embedded \n’s with non-whitespace characters between them. This
seems sufficiently improbable, however the argument “-nobrace” can be
used to force a single argument to be handled as a single argument.
This could conceivably be used with machine-generated Expect code.
Similarly, -brace forces a single argument to be handle as multiple


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

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

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

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

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

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

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/bin

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

spawn date
sleep 20

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

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

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

send “speed 9600\r”;
sleep 1
expect {
timeout {send “\r”; exp_continue}

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

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

There are a couple of things about Expect that may be non-intuitive.
This section attempts to address some of these things with a couple of

A common expect problem is how to recognize shell prompts. Since these
are customized differently by differently people and different shells,
portably automating rlogin can be difficult without knowing the prompt.
A reasonable convention is to have users store a regular expression
describing their prompt (in particular, the end of it) in the environ‐
ment variable EXPECT_PROMPT. Code like the following can be used. If
EXPECT_PROMPT doesn’t exist, the code still has a good chance of func‐
tioning 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 what‐
ever 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 . To match this
prompt, you must account for each of these characters. It is a common
mistake not to include the blank. Put the blank in explicitly.

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

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

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

Even depending on line-oriented buffering is unwise. Not only do pro‐
grams rarely make promises about the type of buffering they do, but
system indigestion can break output lines up so that lines break at
seemingly random places. Thus, if you can express the last few charac‐
ters of a prompt when writing patterns, it is wise to do so.

If you are waiting for a pattern in the last output of a program and
the program emits something else instead, you will not be able to
detect that with the timeout keyword. The reason is that expect will
not timeout – instead it will get an eof indication. Use that instead.
Even better, use both. That way if that line is ever moved around, you
won’t have to edit the line itself.

Newlines are usually converted to carriage return, linefeed sequences
when output by the terminal driver. Thus, if you want a pattern that
explicitly matches the two lines, from, say, printf(“foo\nbar”), you
should use the pattern “foo\r\nbar”.

A similar translation occurs when reading from the user, via
expect_user. In this case, when you press return, it will be trans‐
lated to a newline. If Expect then passes that to a program which sets
its terminal to raw mode (like telnet), there is going to be a problem,
as the program expects a true return. (Some programs are actually for‐
giving in that they will automatically translate newlines to returns,
but most don’t.) Unfortunately, there is no way to find out that a
program put its terminal into raw mode.

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, inter‐
actively 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.


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


Don Libes, National Institute of Standards and Technology

Thanks to John Ousterhout for Tcl, and Scott Paisley for inspiration.
Thanks to Rob Savoye for Expect’s autoconfiguration code.

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

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 por‐
tions of them are used.

29 December 1994 EXPECT(1)