Computer Science
EXPECT(1) EXPECT(1)
NAME
expect - programmed dialogue with interactive programs,
Version 5
SYNOPSIS
expect [ -dDinN ] [ -c cmds ] [ -[f|b] ] cmdfile ] [ args
]
INTRODUCTION
Expect is a program that "talks" to other interactive pro-
grams 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 pro-
vides branching and high-level control structures to
direct the dialogue. In addition, the user can take con-
trol and interact directly when desired, afterward return-
ing 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 libex-
pect(3).
The name "Expect" comes from the idea of send/expect
sequences popularized by uucp, kermit and other modem con-
trol programs. However unlike uucp, Expect is generalized
so that it can be run as a user-level command with any
program and task in mind. Expect can actually talk to
several programs at the same time.
For example, here are some things Expect can do:
o Cause your computer to dial you back, so that
you can login without paying for the call.
o 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 con-
trol to you.
o Run fsck, and in response to its questions,
answer "yes", "no" or give control back to you,
based on predetermined criteria.
o Connect to another network or BBS (e.g., MCI
Mail, CompuServe) and automatically retrieve
your mail so that it appears as if it was orig-
inally sent to your local system.
o Carry environment variables, current directory,
or any kind of information across rlogin, tel-
net, tip, su, chgrp, etc.
There are a variety of reasons why the shell cannot per-
form 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 char-
acterized programmatically. Expect can also give the user
back control (without halting the program being con-
trolled) if desired. Similarly, the user can return con-
trol to the script at any time.
USAGE
Expect reads cmdfile for a list of commands to execute.
Expect may also be invoked implicitly on systems which
support the #! notation by marking the script executable,
and making the first line in your script:
#!/usr/local/bin/expect -f
Of course, the path must accurately describe where Expect
lives. /usr/local/bin is just an example.
The -c flag prefaces a command to be executed before any
in the script. The command should be quoted to 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 primar-
ily 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 com-
mand is useful for tracing statements, and the trace com-
mand 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 exe-
cuted 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.)
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 com-
mands instead of reading them from a file. Prompting is
terminated via the exit command or upon EOF. See inter-
preter (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 $exp_library/expect.rc is sourced automatically
if present, unless the -N flag is used. (When using
Expectk, this option is specified as -NORC.) Immediately
after this, the file ~/.expect.rc is sourced automati-
cally, unless the -n flag is used. If the environment
variable DOTDIR is defined, it is treated as a directory
and .expect.rc is read from there. (When using Expectk,
this option is specified as -norc.) This sourcing occurs
only after executing any -c flags.
-v causes Expect to print its version number and exit.
(The corresponding flag in Expectk, which uses long flag
names, is -version.)
Optional args are constructed into a list and stored in
the variable named argv. argc is initialized to the
length of argv.
argv0 is defined to be the name of the script (or binary
if no script is used). For example, the following prints
out the name of the script and the first three arguments:
send_user "$argv0 [lrange $argv 0 2]\n"
COMMANDS
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 cur-
rent 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 pro-
cesses.
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 implic-
itly 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 clos-
ing 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 argu-
ment 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. Com-
pare 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 discon-
nected by the time Expect receives control.
exit [-opts] [status]
causes Expect to exit or otherwise prepare to do so.
The -onexit flag causes the next argument to be used
as an exit handler. Without an argument, the cur-
rent exit handler is returned.
The -noexit flag causes Expect to prepare to exit
but stop short of actually returning control to the
operating system. The user-defined exit handler is
run as well as Expect's own internal handlers. No
further Expect commands should be executed. This is
useful if you are running Expect with other Tcl
extensions. The current interpreter (and main win-
dow 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 han-
dlers 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 sys-
tem-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
The command exp_continue allows expect itself to
continue executing rather than returning as it nor-
mally would. (See expect for more information.)
exp_internal [-f file] value
causes further commands to send diagnostic informa-
tion 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 cur-
rent 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 exe-
cuted on the spawn id.
exp_pid [-i spawn_id]
returns the process id corresponding to the cur-
rently spawned process. If the -i flag is used, the
pid returned corresponds to that of the given spawn
id.
exp_send
is an alias for send.
exp_send_error
is an alias for send_error.
exp_send_log
is an alias for send_log.
exp_send_tty
is an alias for send_tty.
exp_send_user
is an alias for send_user.
exp_version [[-exit] version]
is useful for assuring that the script is compatible
with the current version of Expect.
With no arguments, the current version of Expect is
returned. This version may then be encoded in your
script. If you actually know that you are not using
features of recent versions, you can specify an ear-
lier version.
Versions consist of three numbers separated by dots.
First is the major number. Scripts written for ver-
sions of Expect with a different major number will
almost certainly not work. exp_version returns an
error if the major numbers do not match.
Second is the minor number. Scripts written for a
version with a greater minor number than the current
version may depend upon some new feature and might
not run. exp_version returns an error if the major
numbers match, but the script minor number is
greater than that of the running Expect.
Third is a number that plays no part in the version
comparison. However, it is incremented when the
Expect software distribution is changed in any way,
such as by additional documentation or optimization.
It is reset to 0 upon each new minor version.
With the -exit flag, Expect prints an error and
exits if the version is out of date.
expect [[-opts] pat1 body1] ... [-opts] patn [bodyn]
waits until one of the patterns matches the output
of a spawned process, a specified time period has
passed, or an end-of-file is seen. If the final
body is empty, it may be omitted.
Patterns from the most recent expect_before command
are implicitly used before any other patterns. Pat-
terns from the most recent expect_after command are
implicitly used after any other patterns.
If the arguments to the entire expect statement
require more than one line, all the arguments may be
"braced" into one so as to avoid terminating each
line with a backslash. In this one case, the usual
Tcl substitutions will occur despite the braces.
If a pattern is the keyword eof, the corresponding
body is executed upon end-of-file. If a pattern is
the keyword timeout, the corresponding body is exe-
cuted 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 appear-
ing 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 pat-
tern 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 suc-
cessful 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") com-
mand. 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 charac-
ters 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 indi-
gestion.")
The -ex flag causes the pattern to be matched as an
"exact" string. No interpretation of *, ^, etc is
made (although the usual Tcl conventions must still
be observed). Exact patterns are always unanchored.
The -nocase flag causes uppercase characters of the
output to compare as if they were lowercase charac-
ters. The pattern is not affected.
While reading output, more than 2000 bytes can force
earlier bytes to be "forgotten". This may be
changed with the function match_max. (Note that
excessively large values can slow down the pattern
matcher.) If patlist is full_buffer, the corre-
sponding 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 corre-
sponding 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 vari-
ables 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 "-n" for convenience while experi-
menting).
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 sep-
arated list of spawn_ids or a variable referring to
such a list of spawn_ids.
For example, the following example waits for "con-
nected" 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 asso-
ciated 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_back-
ground 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 pat-
terns 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 pat-
terns match against the spawn id defined at the time
that the expect_before command was executed (not
when its pattern is matched).
The -info flag causes expect_before to return the
current specifications of what patterns it will
match. By default, it reports on the current spawn
id. An optional spawn id specification may be given
for information on that spawn id. For example
expect_before -info -i $proc
At most one spawn id specification may be given.
The flag -indirect suppresses direct spawn ids that
come only from indirect specifications.
Instead of a spawn id specification, the flag "-all"
will cause "-info" to report on all spawn ids.
The output of the -info flag can be reused as the
argument to expect_before.
expect_tty [expect_args]
is like expect but it reads characters from /dev/tty
(i.e. keystrokes from the user). By default, read-
ing is performed in cooked mode. Thus, lines must
end with a return in order for expect to see them.
This may be changed via stty (see the stty command
below).
expect_user [expect_args]
is like expect but it reads characters from stdin
(i.e. keystrokes from the user). By default, read-
ing is performed in cooked mode. Thus, lines must
end with a return in order for expect to see them.
This may be changed via stty (see the stty command
below).
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 pro-
cess 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 pro-
cesses, the result can be confusing.
Some pty implementations may be confused by multiple
readers and writers, even momentarily. Thus, it is
safest to fork before spawning processes.
interact [string1 body1] ... [stringn [bodyn]]
gives control of the current process to the user, so
that keystrokes are sent to the current process, and
the stdout and stderr of the current process are
returned.
String-body pairs may be specified as arguments, in
which case the body is executed when the correspond-
ing string is entered. (By default, the string is
not sent to the current process.) The interpreter
command is assumed, if the final body is missing.
If the arguments to the entire interact statement
require more than one line, all the arguments may be
"braced" into one so as to avoid terminating each
line with a backslash. In this one case, the usual
Tcl substitutions will occur despite the braces.
For example, the following command runs interact
with the following string-body pairs defined: When
^Z is pressed, Expect is suspended. (The -reset
flag restores the terminal modes.) When ^A is
pressed, the user sees "you typed a control-A" and
the process is sent a ^A. When $ is pressed, the
user sees the date. When ^C is pressed, Expect
exits. If "foo" is entered, the user sees "bar".
When ~~ is pressed, the Expect interpreter runs
interactively.
set CTRLZ \032
interact {
-reset $CTRLZ {exec kill -STOP [pid]}
\001 {send_user "you typed a control-A\n";
send "\001"
}
$ {send_user "The date is [exec date]."}
\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 charac-
ters 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 sub-
strings 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 sub-
strings are stored in the variable interact_out sim-
ilarly 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 exe-
cuted 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 sec-
onds) and action that is executed after no charac-
ters have been read for a given time. The timeout
pattern applies to the most recently specified pro-
cess. 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 corre-
sponding 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 char-
acters 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 press the 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 fol-
lowing pattern back to the process that generated
them as each character is read. This may be useful
when the user needs to see feedback from partially
typed patterns.
If a pattern is being echoed but eventually fails to
match, the characters are sent to the spawned pro-
cess. If the spawned process then echoes them, the
user will see the characters twice. -echo is proba-
bly only appropriate in situations where the user is
unlikely to not complete the pattern. For example,
the following excerpt is from rftp, the recursive-
ftp script, where the user is prompted to enter ~g,
~p, or ~l, to get, put, or list the current direc-
tory 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 char-
acters 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 "[exec date]: 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 inter-
act 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 argu-
ment (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 infor-
mation). For the same reason, the interpreter com-
mand 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 speci-
fied, it overrides $user_spawn_id. If a second
-input is specified, it overrides $spawn_id. Addi-
tional -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
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 prompt-
ing 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 proce-
dure called "prompt2".
During interpreter, cooked mode is used, even if the
its caller was using raw mode.
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 sup-
pressed by the log_user command.
By default, the log_file command appends to old
files rather than truncating them, for the conve-
nience of being able to turn logging off and on mul-
tiple times in one session. To truncate files, use
the -noappend flag.
The -info flag causes log_file to return a descrip-
tion 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 std-
out 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 descrip-
tion of the most recent non-info arguments given.
match_max [-d] [-i spawn_id] [size]
defines the size of the buffer (in bytes) used
internally by expect. With no size argument, the
current size is returned.
With the -d flag, the default size is set. (The
initial default is 2000.) With the -i flag, the
size is set for the named spawn id, otherwise it is
set for the current process.
overlay [-# spawn_id] [-# spawn_id] [...] program [args]
executes program args in place of the current Expect
program, which terminates. A bare hyphen argument
forces a hyphen in front of the command name as if
it was a login shell. All spawn_ids are closed
except for those named as arguments. These are
mapped onto the named file identifiers.
Spawn_ids are mapped to file identifiers for the new
program to inherit. For example, the following line
runs chess and allows it to be controlled by the
current process - say, a chess master.
overlay -0 $spawn_id -1 $spawn_id -2 $spawn_id chess
This is more efficient than "interact -u", however,
it sacrifices the ability to do programmed interac-
tion since the Expect process is no longer in con-
trol.
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 pro-
cess.
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 charac-
ters until a return character is sent. A return
character is denoted "\r".
The -- flag forces the next argument to be inter-
preted 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 mecha-
nism 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 it 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 num-
ber 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 ele-
ments 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 vari-
able, and 10 is quite invariable. The extremes are
0 to infinity. The last two parameters are, respec-
tively, a minimum and maximum interarrival time.
The minimum and maximum are used last and "clip" the
final time. The ultimate average can be quite dif-
ferent 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 argu-
ment.
The flags for sending null characters, for sending
breaks, for forcing slow output and for human-style
output are mutually exclusive. Only the one speci-
fied last will be used. Furthermore, no string argu-
ment 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 pro-
cess 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 compat-
ibility 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 std-
out rather than the current process.
sleep seconds
causes the script to sleep for the given number of
seconds. Seconds may be a decimal number. Inter-
rupts (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-
fiers.
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 con-
sidered 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 argu-
ments. The -noecho flag stops spawn from doing
this.
The -console flag causes console output to be redi-
rected to the spawned process. This is not sup-
ported 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 termi-
nals 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 inter-
preted 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 iden-
tifier. 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 pro-
cess 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 vari-
ables.) 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 argu-
ments should not be grouped into a single argument.)
Requests for status return it as the result of the
command. If no status is requested and the control-
ling terminal is accessed, the previous status of
the raw and echo attributes are returned in a form
which can later be used by the command.
For example, the arguments raw or -cooked put the
terminal into raw mode. The arguments -raw or
cooked put the terminal into cooked mode. The argu-
ments 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 charac-
ters 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 cur-
rently being executed.
The -code flag uses the return code of the command
in place of whatever code Tcl was about to return
when the command originally started running.
The -interp flag causes the command to be evaluated
using the interpreter active at the time the command
started running rather than when the trap was
declared.
The -name flag causes the trap command to return the
signal name of the trap command currently being exe-
cuted.
The -max flag causes the trap command to return the
largest signal number that can be set.
For example, the command "trap {send_user "Ouch!"}
SIGINT" will print "Ouch!" each time the user
presses ^C.
By default, SIGINT (which can usually be generated
by pressing ^C) and SIGTERM cause Expect to exit.
This is due to the following trap, created by
default when Expect starts.
trap exit {SIGINT SIGTERM}
If you use the -D flag to start the debugger, SIGINT
is redefined to start the interactive debugger.
This is due to the following trap:
trap {exp_debug 1} SIGINT
The debugger trap can be changed by setting the
environment variable EXPECT_DEBUG_INIT to a new trap
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 dur-
ing subsequent spawn commands.
See signal(3) for more info.
wait [args]
delays until a spawned process (or the current pro-
cess 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 correspond-
ing spawn id. The third integer is -1 if an operat-
ing system error occurred, or 0 otherwise. If the
third integer was 0, the fourth integer is the sta-
tus 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 vari-
able 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 correspond-
ing 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 immedi-
ately with the indication of a successful wait.
When the process exits (later), it will automati-
cally disappear without the need for an explicit
wait.
The wait command may also be used wait for a forked
process using the arguments "-i -1". Unlike its use
with spawned processes, this command can be executed
at any time. There is no control over which process
is reaped. However, the return value can be checked
for the process id.
LIBRARIES
Expect automatically knows about two built-in libraries
for Expect scripts. These are defined by the 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
A vgrind definition is available for pretty-printing
Expect scripts. Assuming the vgrind definition supplied
with the Expect distribution is correctly installed, you
can use it as:
vgrind -lexpect file
EXAMPLES
It many not be apparent how to put everything together
that the man page describes. I encourage you to read and
try out the examples in the example directory of the
Expect distribution. Some of them are real programs.
Others are simply illustrative of certain techniques, and
of course, a couple are just quick hacks. The INSTALL
file has a quick overview of these programs.
The Expect papers (see SEE ALSO) are also useful. While
some papers use syntax corresponding to earlier versions
of Expect, the accompanying rationales are still valid and
go into a lot more detail than this man page.
CAVEATS
Extensions may collide with Expect's command names. For
example, send is defined by Tk for an entirely 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 partic-
ular, 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 obvi-
ates 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. Unfor-
tunately, this can make things unpleasant for other pro-
grams. 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 set-
ting 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 echo-
ing 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 embed-
ded \n's with non-whitespace characters between them.
This seems sufficiently improbable, however the argument
"-brace" can be used to force a single argument to be han-
dled as a single argument. This could conceivably be used
with machine-generated Expect code.
BUGS
It was really tempting to name the program "sex" (for
either "Smart EXec" or "Send-EXpect"), but good sense (or
perhaps just Puritanism) prevailed.
On some systems, when a shell is spawned, it complains
about not being able to access the tty but runs anyway.
This means your system has a mechanism for gaining the
controlling tty that Expect doesn't know about. Please
find out what it is, and send this information back to me.
Ultrix 4.1 (at least the latest versions around here) con-
siders 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 suf-
fices 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 environ-
ment 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 ker-
nel throws away any unread output after 10 to 15 seconds
(actual number is implementation-dependent) after the pro-
cess 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 situa-
tion in which the final output of a truly interactive pro-
gram 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 sec-
ond 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}
$prompt
}
EXPECT HINTS
There are a couple of things about Expect that may be non-
intuitive. This section attempts to address some of these
things with a couple of suggestions.
A common expect problem is how to recognize shell prompts.
Since these are customized differently by differently peo-
ple and different shells, portably automating rlogin can
be difficult without knowing the prompt. A reasonable
convention is to have users store a regular expression
describing their prompt (in particular, the end of it) in
the environment variable EXPECT_PROMPT. Code like the
following can be used. If EXPECT_PROMPT doesn't exist,
the code still has a good chance of functioning correctly.
set prompt "(%|#|\\$) $" ;# 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 possi-
bility 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 con-
fusing because the phrase "last thing received" can vary
depending upon the speed of the computer and the process-
ing 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 bet-
ter, 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, line-
feed 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 pro-
gram expects a true return. (Some programs are actually
forgiving in that they will automatically translate new-
lines 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 prompt-
ing for passwords from a script is a smarter idea than
embedding them literally. Nonetheless, sometimes such
embedding is the only possibility.
Unfortunately, the UNIX file system has no direct way of
creating scripts which are executable but unreadable.
Systems which support setgid shell scripts may indirectly
simulate this as follows:
Create the Expect script (that contains the secret data)
as usual. Make its permissions be 750 (-rwxr-x---) and
owned by a trusted group, i.e., a group which is allowed
to read it. If necessary, create a new group for this
purpose. Next, create a /bin/sh script with permissions
2751 (-rwxr-s--x) owned by the same group as before.
The result is a script which may be executed (and read) by
anyone. When invoked, it runs the Expect script.
SEE ALSO
Tcl(3), libexpect(3)
"Exploring Expect: A Tcl-Based Toolkit for Automating
Interactive Programs" by Don Libes, pp. 602, ISBN
1-56592-090-2, O'Reilly and Associates, 1995.
"expect: Curing Those Uncontrollable Fits of Interactiv-
ity" 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 Installa-
tion 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, Washing-
ton, 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, Proceed-
ings of the 1993 Tcl/Tk Workshop, Berkeley, CA, June
10-11, 1993.
AUTHOR
Don Libes, National Institute of Standards and Technology
ACKNOWLEDGMENTS
Thanks to John Ousterhout for Tcl, and Scott Paisley for
inspiration. Thanks to Rob Savoye for Expect's autocon-
figuration code.
The HISTORY file documents much of the evolution of
expect. It makes interesting reading and might give you
further insight to this software. Thanks to the people
mentioned in it who sent me bug fixes and gave other
assistance.
Design and implementation of Expect was paid for in part
by the U.S. government and is therefore in the public
domain. However the author and NIST would like credit if
this program and documentation or portions of them are
used.
29 December 1994 1
Back to the index
