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NAME
expect - programmed dialogue with interactive programs, Ver-
sion 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 control and
interact directly when desired, afterward returning control
to the script.
Expectk is a mixture of Expect and Tk. It behaves just like
Expect and Tk's wish. Expect can also be used directly in C
or C++ (that is, without Tcl). See libexpect(3).
The name "Expect" comes from the idea of send/expect
sequences popularized by uucp, kermit and other modem con-
trol programs. However unlike uucp, Expect is generalized
so that it can be run as a user-level command with any pro-
gram 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 con-
figuration doesn't appear, restart it (again and
again) until it does, then hand over control 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 originally sent to
your local system.
o 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 character-
ized programmatically. Expect can also give the user back
control (without halting the program being controlled) if
desired. Similarly, the user can return control to the
script at any time.
USAGE
Expect reads cmdfile for a list of commands to execute.
Expect may also be invoked implicitly on systems which sup-
port the #! notation by marking the script executable, and
making the first line in your script:
#!/usr/local/bin/expect -f
Of course, the path must accurately describe where Expect
lives. /usr/local/bin is just an example.
The -c flag prefaces a command to be executed before any in
the script. The command should be quoted to prevent being
broken up by the shell. This option may be used multiple
times. Multiple commands may be executed with a single -c
by separating them with semicolons. Commands are executed
in the order they appear. (When using Expectk, this option
is specified as -command.)
The -d flag enables some diagnostic output, which primarily
reports internal activity of commands such as expect and
interact. This flag has the same effect as "exp_internal 1"
at the beginning of an Expect script, plus the version of
Expect is printed. (The strace command is useful for trac-
ing 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 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 nei-
ther a command file nor -c is used. (When using Expectk,
this option is specified as -interactive.)
-- may be used to delimit the end of the options. This is
useful if you want to pass an option-like argument to your
script without it being interpreted by Expect. This can
usefully be placed in the #! line to prevent any flag-like
interpretation by Expect. For example, the following will
leave the original arguments (including the script name) in
the variable argv.
#!/usr/local/bin/expect --
Note that the usual getopt(3) and execve(2) conventions must
be observed when adding arguments to the #! line.
The file $exp_library/expect.rc is sourced automatically if
present, unless the -N flag is used. (When using Expectk,
this option is specified as -NORC.) Immediately after this,
the file ~/.expect.rc is sourced automatically, unless the
-n flag is used. If the environment variable DOTDIR is
defined, it is treated as a directory and .expect.rc is read
from there. (When using Expectk, this option is specified
as -norc.) This sourcing occurs only after executing any -c
flags.
-v causes Expect to print its version number and exit. (The
corresponding flag in Expectk, which uses long flag names,
is -version.)
Optional args are constructed into a list and stored in the
variable named argv. argc is initialized to the length of
argv.
argv0 is defined to be the name of the script (or binary if
no script is used). For example, the following prints out
the name of the script and the first three arguments:
send_user "$argv0 [lrange $argv 0 2]\n"
COMMANDS
Expect uses Tcl (Tool Command Language). Tcl provides con-
trol flow (e.g., if, for, break), expression evaluation and
several other features such as recursion, procedure defini-
tion, 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 pro-
cess 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 pro-
cess is overlayed. To leave a spawn id open, use the
value 0. A non-zero integer value will force the
spawn closed (the default) in any new processes.
The -slave flag closes the slave associated with the
spawn id. (See "spawn -pty".) When the connection is
closed, the slave is automatically closed as well if
still open.
No matter whether the connection is closed implicitly
or explicitly, you should call wait to clear up the
corresponding kernel process slot. close does not
call wait since there is no guarantee that closing a
process connection will cause it to exit. See wait
below for more info.
debug [[-now] 0|1]
controls a Tcl debugger allowing you to step through
statements, set breakpoints, etc.
With no arguments, a 1 is returned if the debugger is
not running, otherwise a 0 is returned.
With a 1 argument, the debugger is started. With a 0
argument, the debugger is stopped. If a 1 argument is
preceded by the -now flag, the debugger is started
immediately (i.e., in the middle of the debug command
itself). Otherwise, the debugger is started with the
next Tcl statement.
The debug command does not change any traps. Compare
this to starting Expect with the -D flag (see above).
See the README file or SEE ALSO (below) for more
information on the debugger.
disconnect
disconnects a forked process from the terminal. It
continues running in the background. The process is
given its own process group (if possible). Standard
I/O is redirected to /dev/null.
The following fragment uses disconnect to continue
running the script in the background.
if {[fork]!=0} exit
disconnect
. . .
The following script reads a password, and then runs a
program every hour that demands a password each time
it is run. The script supplies the password so that
you only have to type it once. (See the stty command
which demonstrates how to turn off password echoing.)
send_user "password?\ "
expect_user -re "(.*)\n"
for {} 1 {} {
if {[fork]!=0} {sleep 3600;continue}
disconnect
spawn priv_prog
expect Password:
send "$expect_out(1,string)\r"
. . .
exit
}
An advantage to using disconnect over the shell asyn-
chronous 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 parame-
ters since the terminal is already disconnected by the
time Expect receives control.
exit [-opts] [status]
causes Expect to exit or otherwise prepare to do so.
The -onexit flag causes the next argument to be used
as an exit handler. Without an argument, the current
exit handler is returned.
The -noexit flag causes Expect to prepare to exit but
stop short of actually returning control to the
operating system. The user-defined exit handler is
run as well as Expect's own internal handlers. No
further Expect commands should be executed. This is
useful if you are running Expect with other Tcl exten-
sions. The current interpreter (and main window if in
the Tk environment) remain so that other Tcl exten-
sions can clean up. If Expect's exit is called again
(however this might occur), the handlers are not
rerun.
Upon exiting, all connections to spawned processes are
closed. Closure will be detected as an EOF by spawned
processes. exit takes no other actions beyond what
the normal _exit(2) procedure does. Thus, spawned
processes that do not check for EOF may continue to
run. (A variety of conditions are important to deter-
mining, for example, what signals a spawned process
will be sent, but these are system-dependent, typi-
cally 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 con-
tinue executing rather than returning as it normally
would. (See expect for more information.)
exp_internal [-f file] value
causes further commands to send diagnostic information
internal to Expect to stderr if value is non-zero.
This output is disabled if value is 0. The diagnostic
information includes every character received, and
every attempt made to match the current output against
the patterns.
If the optional file is supplied, all normal and
debugging output is written to that file (regardless
of the value of value). Any previous diagnostic out-
put 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 currently
spawned process. If the -i flag is used, the pid
returned corresponds to that of the given spawn id.
exp_send
is an alias for send.
exp_send_error
is an alias for send_error.
exp_send_log
is an alias for send_log.
exp_send_tty
is an alias for send_tty.
exp_send_user
is an alias for send_user.
exp_version [[-exit] version]
is useful for assuring that the script is compatible
with the current version of Expect.
With no arguments, the current version of Expect is
returned. This version may then be encoded in your
script. If you actually know that you are not using
features of recent versions, you can specify an ear-
lier version.
Versions consist of three numbers separated by dots.
First is the major number. Scripts written for 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
executed upon timeout. If no timeout keyword is used,
an implicit null action is executed upon timeout. The
default timeout period is 10 seconds but may be set,
for example to 30, by the command "set timeout 30".
An infinite timeout may be designated by the value -1.
If a pattern is the keyword default, the corresponding
body is executed upon either timeout or end-of-file.
If a pattern matches, then the corresponding body is
executed. expect returns the result of the body (or
the empty string if no pattern matched). In the event
that multiple patterns match, the one appearing first
is used to select a body.
Each time new output arrives, it is compared to each
pattern in the order they are listed. Thus, you may
test for absence of a match by making the last pattern
something guaranteed to appear, such as a prompt. In
situations where there is no prompt, you must use
timeout (just like you would if you were interacting
manually).
Patterns are specified in three ways. By default,
patterns are specified as with Tcl's string match com-
mand. (Such patterns are also similar to C-shell reg-
ular expressions usually referred to as "glob" pat-
terns). The -gl flag may may be used to protect pat-
terns 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 form-
ing glob-style patterns can be found in the Tcl
manual.
Regexp-style patterns follow the syntax defined by
Tcl's regexp (short for "regular expression") command.
regexp patterns are introduced with the flag -re. The
previous example can be rewritten using a regexp as:
expect {
busy {puts busy\n ; exp_continue}
-re "failed|invalid password" abort
timeout abort
connected
}
Both types of patterns are "unanchored". This means
that patterns do not have to match the entire string,
but can begin and end the match anywhere in the string
(as long as everything else matches). Use ^ to match
the beginning of a string, and $ to match the end.
Note that if you do not wait for the end of a string,
your responses can easily end up in the middle of the
string as they are echoed from the spawned process.
While still producing correct results, the output can
look unnatural. Thus, use of $ is encouraged if you
can exactly describe the characters at the end of a
string.
Note that in many editors, the ^ and $ match the
beginning and end of lines respectively. However,
because expect is not line oriented, these characters
match the beginning and end of the data (as opposed to
lines) currently in the expect matching buffer.
(Also, see the note below on "system indigestion.")
The -ex flag causes the pattern to be matched as an
"exact" string. No interpretation of *, ^, etc is
made (although the usual Tcl conventions must still be
observed). Exact patterns are always unanchored.
The -nocase flag causes uppercase characters of the
output to compare as if they were lowercase charac-
ters. The pattern is not affected.
While reading output, more than 2000 bytes can force
earlier bytes to be "forgotten". This may be changed
with the function match_max. (Note that excessively
large values can slow down the pattern matcher.) If
patlist is full_buffer, the corresponding body is exe-
cuted if match_max bytes have been received and no
other patterns have matched. Whether or not the
full_buffer keyword is used, the forgotten characters
are written to expect_out(buffer).
If patlist is the keyword null, and nulls are allowed
(via the remove_nulls command), the corresponding body
is executed if a single ASCII 0 is matched. It is not
possible to match 0 bytes via glob or regexp patterns.
Upon matching a pattern (or eof or full_buffer), any
matching and previously unmatched output is saved in
the variable expect_out(buffer). Up to 9 regexp sub-
string 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 start-
ing 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 pro-
duced 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 pro-
cess 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 experiment-
ing).
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 "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 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 pro-
vides a way of changing the I/O source while the com-
mand 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 nor-
mally 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 pass-
word.
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 incre-
mented. If "p" is pressed, several returns are sent
to the process, perhaps to poke it in some way, and
"i" lets the user interact with the process, effec-
tively 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 meaning-
less to expect_background and are silently discarded.
Otherwise, the expect_background command uses
expect_before and expect_after patterns just like
expect does.
When expect_background actions are being evaluated,
background processing for the same spawn id is
blocked. Background processing is unblocked when the
action completes. While background processing is
blocked, it is possible to do a (foreground) expect on
the same spawn id.
It is not possible to execute an expect while an
expect_background is unblocked. expect_background for
a particular spawn id is deleted by declaring a new
expect_background with the same spawn id. Declaring
expect_background with no pattern removes the given
spawn id from the ability to match patterns in the
background.
expect_before [expect_args]
takes the same arguments as expect, however it returns
immediately. Pattern-action pairs from the most
recent expect_before with the same spawn id are impli-
citly 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 asso-
ciated body is executed in the context of the expect
command. If patterns from both expect_before and
expect can match, the expect_before pattern is used.
If no pattern is specified, the spawn id is not
checked for any patterns.
Unless overridden by a -i flag, expect_before patterns
match against the spawn id defined at the time that
the expect_before command was executed (not when its
pattern is matched).
The -info flag causes expect_before to return the
current specifications of what patterns it will match.
By default, it reports on the current spawn id. An
optional spawn id specification may be given for
information on that spawn id. For example
expect_before -info -i $proc
At most one spawn id specification may be given. The
flag -indirect suppresses direct spawn ids that come
only from indirect specifications.
Instead of a spawn id specification, the flag "-all"
will cause "-info" to report on all spawn ids.
The output of the -info flag can be reused as the
argument to expect_before.
expect_tty [expect_args]
is like expect but it reads characters from /dev/tty
(i.e. keystrokes from the user). By default, reading
is performed in cooked mode. Thus, lines must end
with a return in order for expect to see them. This
may be changed via stty (see the stty command below).
expect_user [expect_args]
is like expect but it reads characters from stdin
(i.e. keystrokes from the user). By default, reading
is performed in cooked mode. Thus, lines must end
with a return in order for expect to see them. This
may be changed via stty (see the stty command below).
fork creates a new process. The new process is an exact
copy of the current Expect process. On success, fork
returns 0 to the new (child) process and returns the
process ID of the child process to the parent process.
On failure (invariably due to lack of resources, e.g.,
swap space, memory), fork returns -1 to the parent
process, and no child process is created.
Forked processes exit via the exit command, just like
the original process. Forked processes are allowed to
write to the log files. If you do not disable debug-
ging or logging in most of the processes, the result
can be confusing.
Some pty implementations may be confused by multiple
readers and writers, even momentarily. Thus, it is
safest to fork before spawning processes.
interact [string1 body1] ... [stringn [bodyn]]
gives control of the current process to the user, so
that keystrokes are sent to the current process, and
the stdout and stderr of the current process are
returned.
String-body pairs may be specified as arguments, in
which case the body is executed when the corresponding
string is entered. (By default, the string is not
sent to the current process.) The interpreter com-
mand 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 anticipa-
tion of the remainder coming. If characters are then
entered such that there can no longer possibly be a
match, only the part of the string will be sent to the
process that cannot possibly begin another match.
Thus, strings that are substrings of partial matches
can match later, if the original strings that was
attempting to be match ultimately fails.
By default, string matching is exact with no wild
cards. (In contrast, the expect command uses glob-
style patterns by default.) The -ex flag may be used
to protect patterns that might otherwise match
interact flags from doing so. Any pattern beginning
with a "-" should be protected this way. (All
strings starting with "-" are reserved for future
options.)
The -re flag forces the string to be interpreted as a
regexp-style pattern. In this case, matching sub-
strings are stored in the variable interact_out simi-
larly to the way expect stores its output in the vari-
able expect_out. The -indices flag is similarly sup-
ported.
The pattern eof introduces an action that is executed
upon end-of-file. A separate eof pattern may also
follow the -output flag in which case it is matched if
an eof is detected while writing output. The default
eof action is "return", so that interact simply
returns upon any EOF.
The pattern timeout introduces a timeout (in seconds)
and action that is executed after no characters have
been read for a given time. The timeout pattern
applies to the most recently specified process. There
is no default timeout. The special variable "timeout"
(used by the expect command) has no affect on this
timeout.
For example, the following statement could be used to
autologout users who have not typed anything for an
hour but who still get frequent system messages:
interact -input $user_spawn_id timeout 3600 return -output \
$spawn_id
If the pattern is the keyword null, and nulls are
allowed (via the remove_nulls command), the
corresponding body is executed if a single ASCII 0 is
matched. It is not possible to match 0 bytes via glob
or regexp patterns.
Prefacing a pattern with the flag -iwrite causes the
variable interact_out(spawn_id) to be set to the
spawn_id which matched the pattern (or eof).
Actions such as break and continue cause control
structures (i.e., for, proc) to behave in the usual
way. However return causes interact to return to its
caller, while inter_return causes interact to cause a
return in its caller. For example, if "proc foo"
called interact which then executed the action
inter_return, proc foo would return. (This means that
if interact calls interpreter interactively typing
return will cause the interact to continue, while
inter_return will cause the interact to return to its
caller.)
During interact, raw mode is used so that all charac-
ters 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 feature of
the terminal driver on some systems). The only reason
to use -reset is if your action depends on running in
cooked mode.
The -echo flag sends characters that match the follow-
ing 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 pat-
terns.
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 follow-
ing 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 any-
thing else, except mistakenly, in which case, they'll
probably just ignore the result anyway.
interact {
-echo ~g {getcurdirectory 1}
-echo ~l {getcurdirectory 0}
-echo ~p {putcurdirectory}
}
The -nobuffer flag sends characters that match the
following pattern on to the output process as charac-
ters are read.
This is useful when you wish to let a program echo
back the pattern. For example, the following might be
used to monitor where a person is dialing (a Hayes-
style modem). Each time "atd" is seen the script logs
the rest of the line.
proc lognumber {} {
interact -nobuffer -re "(.*)\r" return
puts $log "[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 interact blindly.
The -o flag causes any following key-body pairs to be
applied to the output of the current process. This
can be useful, for example, when dealing with hosts
that send unwanted characters during a telnet session.
By default, interact expects the user to be writing
stdin and reading stdout of the Expect process itself.
The -u flag (for "user") makes interact look for the
user as the process named by its argument (which must
be a spawned id).
This allows two unrelated processes to be joined
together without using an explicit loop. To aid in
debugging, Expect diagnostics always go to stderr (or
stdout for certain logging and debugging information).
For the same reason, the interpreter command will read
interactively from stdin.
For example, the following fragment creates a login
process. Then it dials the user (not shown), and
finally connects the two together. Of course, any
process may be substituted for login. A shell, for
example, would allow the user to work without
supplying an account and password.
spawn login
set login $spawn_id
spawn tip modem
# dial back out to user
# connect user to login
interact -u $login
To send output to multiple processes, list each spawn
id list prefaced by a -output flag. Input for a group
of output spawn ids may be determined by a spawn id
list prefaced by a -input flag. (Both -input and
-output may take lists in the same form as the -i flag
in the expect command, except that any_spawn_id is not
meaningful in interact.) All following flags and
strings (or patterns) apply to this input until
another -input flag appears. If no -input appears,
-output implies "-input $user_spawn_id -output".
(Similarly, with patterns that do not have -input.)
If one -input is specified, it overrides
$user_spawn_id. If a second -input is specified, it
overrides $spawn_id. Additional -input flags may be
specified.
The two implied input processes default to having
their outputs specified as $spawn_id and
$user_spawn_id (in reverse). If a -input flag appears
with no -output flag, characters from that process are
discarded.
The -i flag introduces a replacement for the current
spawn_id when no other -input or -output flags are
used. A -i flag implies a -o flag.
It is possible to change the processes that are being
interacted with by using indirect spawn ids.
(Indirect spawn ids are described in the section on
the expect command.) Indirect spawn ids may be speci-
fied 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 com-
mand causes interpreter to continue prompting for new
commands.
By default, the prompt contains two integers. The
first integer describes the depth of the evaluation
stack (i.e., how many times Tcl_Eval has been called).
The second integer is the Tcl history identifier. The
prompt can be set by defining a procedure called
"prompt1" whose return value becomes the next prompt.
If a statement has open quotes, parens, braces, or
brackets, a secondary prompt (by default "+> ") is
issued upon newline. The secondary prompt may be set
by defining a procedure called "prompt2".
During interpreter, cooked mode is used, even if the
its caller was using raw mode.
log_file [args] [[-a] file]
If a filename is provided, log_file will record a
transcript of the session (beginning at that point) in
the file. log_file will stop recording if no argument
is given. Any previous log file is closed.
Instead of a filename, a Tcl file identifier may be
provided by using the -open or -leaveopen flags. This
is similar to the spawn command. (See spawn for more
info.)
The -a flag forces output to be logged that was
suppressed by the log_user command.
By default, the log_file command appends to old files
rather than truncating them, for the convenience of
being able to turn logging off and on multiple times
in one session. To truncate files, use the -noappend
flag.
The -info flag causes log_file to return a description
of the most recent non-info arguments given.
log_user -info|0|1
By default, the send/expect dialogue is logged to
stdout (and a logfile if open). The logging to stdout
is disabled by the command "log_user 0" and reenabled
by "log_user 1". Logging to the logfile is unchanged.
The -info flag causes log_user to return a description
of the most recent non-info arguments given.
match_max [-d] [-i spawn_id] [size]
defines the size of the buffer (in bytes) used
internally by expect. With no size argument, the
current size is returned.
With the -d flag, the default size is set. (The ini-
tial default is 2000.) With the -i flag, the size is
set for the named spawn id, otherwise it is set for
the current process.
overlay [-# spawn_id] [-# spawn_id] [...] program [args]
executes program args in place of the current Expect
program, which terminates. A bare hyphen argument
forces a hyphen in front of the command name as if it
was a login shell. All spawn_ids are closed except
for those named as arguments. These are mapped onto
the named file identifiers.
Spawn_ids are mapped to file identifiers for the new
program to inherit. For example, the following line
runs chess and allows it to be controlled by the
current process - say, a chess master.
overlay -0 $spawn_id -1 $spawn_id -2 $spawn_id chess
This is more efficient than "interact -u", however, it
sacrifices the ability to do programmed interaction
since the Expect process is no longer in control.
Note that no controlling terminal is provided. Thus,
if you disconnect or remap standard input, programs
that do job control (shells, login, etc) will not
function properly.
parity [-d] [-i spawn_id] [value]
defines whether parity should be retained or stripped
from the output of spawned processes. If value is
zero, parity is stripped, otherwise it is not
stripped. With no value argument, the current value
is returned.
With the -d flag, the default parity value is set.
(The initial default is 1, i.e., parity is not
stripped.) With the -i flag, the parity value is set
for the named spawn id, otherwise it is set for the
current process.
remove_nulls [-d] [-i spawn_id] [value]
defines whether nulls are retained or removed from the
output of spawned processes before pattern matching or
storing in the variable expect_out or interact_out.
If value is 1, nulls are removed. If value is 0,
nulls are not removed. With no value argument, the
current value is returned.
With the -d flag, the default value is set. (The ini-
tial default is 1, i.e., nulls are removed.) With the
-i flag, the value is set for the named spawn id, oth-
erwise it is set for the current process.
Whether or not nulls are removed, Expect will record
null bytes to the log and stdout.
send [-flags] string
Sends string to the current process. For example, the
command
send "hello world\r"
sends the characters, h e l l o <blank> w o r l d
<return> to the current process. (Tcl includes a
printf-like command (called format) which can build
arbitrarily complex strings.)
Characters are sent immediately although programs with
line-buffered input will not read the characters until
a return character is sent. A return character is
denoted "\r".
The -- flag forces the next argument to be interpreted
as a string rather than a flag. Any string can be
preceded by "--" whether or not it actually looks like
a flag. This provides a reliable mechanism to specify
variable strings without being tripped up by those
that accidentally look like flags. (All strings
starting with "-" are reserved for future options.)
The -i flag declares that the string be sent to the
named spawn_id. If the spawn_id is user_spawn_id, and
the terminal is in raw mode, newlines in the string
are translated to return-newline sequences so that
they appear as 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 dev-
ice opened via "spawn -open". If you have spawned a
process such as tip, you should use tip's convention
for generating a break.
The -s flag forces output to be sent "slowly", thus
avoid the common situation where a computer outtypes
an input buffer that was designed for a human who
would never outtype the same buffer. This output is
controlled by the value of the variable "send_slow"
which takes a two element list. The first element is
an integer that describes the number of bytes to send
atomically. The second element is a real number that
describes the number of seconds by which the atomic
sends must be separated. For example, "set send_slow
{10 .001}" would force "send -s" to send strings with
1 millisecond in between each 10 characters sent.
The -h flag forces output to be sent (somewhat) like a
human actually typing. Human-like delays appear
between the characters. (The algorithm is based upon
a Weibull distribution, with modifications to suit
this particular application.) This output is con-
trolled 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 variable, and 10 is
quite invariable. The extremes are 0 to infinity.
The last two parameters are, respectively, a minimum
and maximum interarrival time. The minimum and max-
imum are used last and "clip" the final time. The
ultimate average can be quite different from the given
average if the minimum and maximum clip enough values.
As an example, the following command emulates a fast
and consistent typist:
set send_human {.1 .3 1 .05 2}
send -h "I'm hungry. Let's do lunch."
while the following might be more suitable after a
hangover:
set send_human {.4 .4 .2 .5 100}
send -h "Goodd party lash night!"
Note that errors are not simulated, although you can
set up error correction situations yourself by embed-
ding mistakes and corrections in a send argument.
The flags for sending null characters, for sending
breaks, for forcing slow output and for human-style
output are mutually exclusive. Only the one specified
last will be used. Furthermore, no string argument can
be specified with the flags for sending null charac-
ters or breaks.
It is a good idea to precede the first send to a pro-
cess by an expect. expect will wait for the process
to start, while send cannot. In particular, if the
first send completes before the process starts run-
ning, you run the risk of having your data ignored.
In situations where interactive programs offer no 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 compati-
bility between environments. Similar aliases are pro-
vided for other Expect's other send commands.
send_error [-flags] string
is like send, except that the output is sent to stderr
rather than the current process.
send_log [--] string
is like send, except that the string is only sent to
the log file (see log_file.) The arguments are
ignored if no log file is open.
send_tty [-flags] string
is like send, except that the output is sent to
/dev/tty rather than the current process.
send_user [-flags] string
is like send, except that the output is sent to stdout
rather than the current process.
sleep seconds
causes the script to sleep for the given number of
seconds. Seconds may be a decimal number. Interrupts
(and Tk events if you are using Expectk) are processed
while Expect sleeps.
spawn [args] program [args]
creates a new process running program args. Its
stdin, stdout and stderr are connected to Expect, so
that they may be read and written by other Expect com-
mands. The connection is broken by close or if the
process itself closes any of the file identifiers.
When a process is started by spawn, the variable
spawn_id is set to a descriptor referring to that pro-
cess. The process described by spawn_id is considered
the current process. spawn_id may be read or written,
in effect providing job control.
user_spawn_id is a global variable containing a
descriptor which refers to the user. For example,
when spawn_id is set to this value, expect behaves
like expect_user.
error_spawn_id is a global variable containing a
descriptor which refers to the standard error. For
example, when spawn_id is set to this value, send
behaves like send_error.
tty_spawn_id is a global variable containing a
descriptor which refers to /dev/tty. If /dev/tty does
not exist (such as in a cron, at, or batch script),
then tty_spawn_id is not defined. This may be tested
as:
if {[info vars tty_spawn_id]} {
# /dev/tty exists
} else {
# /dev/tty doesn't exist
# probably in cron, batch, or at script
}
spawn returns the UNIX process id. If no process is
spawned, 0 is returned. The variable
spawn_out(slave,name) is set to the name of the pty
slave device.
By default, spawn echoes the command name and argu-
ments. The -noecho flag stops spawn from doing this.
The -console flag causes console output to be
redirected 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 inter-
preted in the style of stty arguments as further con-
figuration. For example, "set stty_init raw" will
cause further spawned processes's terminals to start
in raw mode. -nottycopy skips the initialization
based on the user's tty. -nottyinit skips the "sane"
initialization.
Normally, spawn takes little time to execute. If you
notice spawn taking a significant amount of time, it
is probably encountering ptys that are wedged. A
number of tests are run on ptys to avoid entanglements
with errant processes. (These take 10 seconds per
wedged pty.) Running Expect with the -d option will
show if Expect is encountering many ptys in odd
states. If you cannot kill the processes to which
these ptys are attached, your only recourse may be to
reboot.
If program cannot be spawned successfully because
exec(2) fails (e.g. when program doesn't exist), an
error message will be returned by the next interact or
expect command as if program had run and produced the
error message as output. This behavior is a natural
consequence of the implementation of spawn. Inter-
nally, 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 identif-
ier. 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 asso-
ciated process. Spawn_id is set as usual.
The variable spawn_out(slave,fd) is set to a file
identifier corresponding to the pty slave. It can be
closed using "close -slave".
The -ignore flag names a signal to be ignored in the
spawned process. Otherwise, signals get the default
behavior. Signals are named as in the trap command,
except that each signal requires a separate flag.
strace level
causes following statements to be printed before being
executed. (Tcl's trace command traces variables.)
level indicates how far down in the call stack to
trace. For example, the following command runs Expect
while tracing the first 4 levels of calls, but none
below that.
expect -c "strace 4" script.exp
The -info flag causes strace to return a description
of the most recent non-info arguments given.
stty args
changes terminal modes similarly to the external stty
command.
By default, the controlling terminal is accessed.
Other terminals can be accessed by appending "<
/dev/tty..." to the command. (Note that the arguments
should not be grouped into a single argument.)
Requests for status return it as the result of the
command. If no status is requested and the control-
ling terminal is accessed, the previous status of the
raw and echo attributes are returned in a form which
can later be used by the command.
For example, the arguments raw or -cooked put the ter-
minal into raw mode. The arguments -raw or cooked put
the terminal into cooked mode. The arguments echo and
-echo put the terminal into echo and noecho mode
respectively.
The following example illustrates how to temporarily
disable echoing. This could be used in otherwise-
automatic scripts to avoid embedding passwords in
them. (See more discussion on this under EXPECT HINTS
below.)
stty -echo
send_user "Password: "
expect_user -re "(.*)\n"
set password $expect_out(1,string)
stty echo
system args
gives args to sh(1) as input, just as if it had been
typed as a command from a terminal. Expect waits
until the shell terminates. The return status from sh
is handled the same way that exec handles its return
status.
In contrast to exec which redirects stdin and stdout
to the script, system performs no redirection (other
than that indicated by the string itself). Thus, it
is possible to use programs which must talk directly
to /dev/tty. For the same reason, the results of sys-
tem 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 numeri-
cally or symbolically as per signal(3). The "SIG"
prefix may be omitted.
With no arguments (or the argument -number), trap
returns the signal number of the trap command
currently being executed.
The -code flag uses the return code of the command in
place of whatever code Tcl was about to return when
the command originally started running.
The -interp flag causes the command to be evaluated
using the interpreter active at the time the command
started running rather than when the trap was
declared.
The -name flag causes the trap command to return the
signal name of the trap command currently being exe-
cuted.
The -max flag causes the trap command to return the
largest signal number that can be set.
For example, the command "trap {send_user "Ouch!"}
SIGINT" will print "Ouch!" each time the user presses
^C.
By default, SIGINT (which can usually be generated by
pressing ^C) and SIGTERM cause Expect to exit. This
is due to the following trap, created by default when
Expect starts.
trap exit {SIGINT SIGTERM}
If you use the -D flag to start the debugger, SIGINT
is redefined to start the interactive debugger. This
is due to the following trap:
trap {exp_debug 1} SIGINT
The debugger trap can be changed by setting the
environment variable EXPECT_DEBUG_INIT to a new trap
command.
You can, of course, override both of these just by
adding trap commands to your script. In particular,
if you have your own "trap exit SIGINT", this will
override the debugger trap. This is useful if you
want to prevent users from getting to the debugger at
all.
If you want to define your own trap on SIGINT but
still trap to the debugger when it is running, use:
if ![exp_debug] {trap mystuff SIGINT}
Alternatively, you can trap to the debugger using some
other signal.
trap will not let you override the action for SIGALRM
as this is used internally to Expect. The disconnect
command sets SIGALRM to SIG_IGN (ignore). You can
reenable this as long as you disable it during subse-
quent spawn commands.
See signal(3) for more info.
wait [args]
delays until a spawned process (or the current process
if none is named) terminates.
wait normally returns a list of four integers. The
first integer is the pid of the process that was
waited upon. The second integer is the corresponding
spawn id. The third integer is -1 if an operating
system error occurred, or 0 otherwise. If the third
integer was 0, the fourth integer is the status
returned by the spawned process. If the third integer
was -1, the fourth integer is the value of errno set
by the operating system. The global variable error-
Code is also set.
Additional elements may appear at the end of the
return value from wait. An optional fifth element
identifies a class of information. Currently, the
only possible value for this element is CHILDKILLED in
which case the next two values are the C-style signal
name and a short textual description.
The -i flag declares the process to wait corresponding
to the named spawn_id (NOT the process id). Inside a
SIGCHLD handler, it is possible to wait for any
spawned process by using the spawn id -1.
The -nowait flag causes the wait to return immediately
with the indication of a successful wait. When the
process exits (later), it will automatically disappear
without the need for an explicit wait.
The wait command may also be used wait for a forked
process using the arguments "-i -1". Unlike its use
with spawned processes, this command can be executed
at any time. There is no control over which process
is reaped. However, the return value can be checked
for the process id.
LIBRARIES
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 distri-
bution. 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 begin-
ning 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 particu-
lar, variables read by commands specific to the Expect pro-
gram will be sought first from the local scope, and if not
found, in the global scope. For example, this obviates the
need to place "global timeout" in every procedure you write
that uses expect. On the other hand, variables written are
always in the local scope (unless a "global" command has
been issued). The most common problem this causes is when
spawn is executed in a procedure. Outside the procedure,
spawn_id no longer exists, so the spawned process is no
longer accessible simply because of scoping. Add a "global
spawn_id" to such a procedure.
If you cannot enable the multispawning capability (i.e.,
your system supports neither select (BSD *.*), poll (SVR>2),
nor something equivalent), Expect will only be able to con-
trol 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" map-
pings: newlines get mapped to newlines instead of carriage-
return newlines, and echoing is disabled. This allows one
to use emacs to edit the input line. Unfortunately, Expect
cannot possibly guess this.
You can request that Expect not override its default setting
of terminal parameters, but you must then be very careful
when writing scripts for such environments. In the case of
emacs, avoid depending upon things like echoing and end-of-
line mappings.
The commands that accepted arguments braced into a single
list (the expect variants and interact) use a heuristic to
decide if the list is actually one argument or many. The
heuristic can fail only in the case when the list actually
does represent a single argument which has multiple embedded
\n's with non-whitespace characters between them. This
seems sufficiently improbable, however the argument
"-nobrace" can be used to force a single argument to be 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 control-
ling 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 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 some-
thing! The following probably suffices for most cases.
set env(SHELL) /bin/sh
set env(HOME) /usr/local/bin
Some implementations of ptys are designed so that the kernel
throws away any unread output after 10 to 15 seconds (actual
number is implementation-dependent) after the process has
closed the file descriptor. Thus Expect programs such as
spawn date
sleep 20
expect
will fail. To avoid this, invoke non-interactive programs
with exec rather than spawn. While such situations are con-
ceivable, in practice I have never encountered a situation
in which the final output of a truly interactive program
would be lost due to this behavior.
On the other hand, Cray UNICOS ptys throw away any unread
output immediately after the process has closed the file
descriptor. I have reported this to Cray and they are work-
ing on a fix.
Sometimes a delay is required between a prompt and a
response, such as when a tty interface is changing UART set-
tings or matching baud rates by looking for start/stop bits.
Usually, all this is require is to sleep for a second or
two. A more robust technique is to retry until the hardware
is ready to receive input. The following example uses both
strategies:
send "speed 9600\r";
sleep 1
expect {
timeout {send "\r"; exp_continue}
$prompt
}
EXPECT HINTS
There are a couple of things about Expect that may be non-
intuitive. This section attempts to address some of these
things with a couple of suggestions.
A common expect problem is how to recognize shell prompts.
Since these are customized differently by differently people
and different shells, portably automating rlogin can be dif-
ficult without knowing the prompt. A reasonable convention
is to have users store a regular expression describing their
prompt (in particular, the end of it) in the environment
variable EXPECT_PROMPT. Code like the following can be
used. If EXPECT_PROMPT doesn't exist, the code still has a
good chance of functioning correctly.
set prompt "(%|#|\\$) $" ;# 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 confus-
ing 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 pro-
duce output one line at a time. Assuming this is the case,
the * in the pattern of the previous paragraph may only
match the end of the current line even though there seems to
be more, because at the time of the match that was all the
output that had been received.
expect has no way of knowing that further output is coming
unless your pattern specifically accounts for it.
Even depending on line-oriented buffering is unwise. Not
only do programs rarely make promises about the type of
buffering they do, but system indigestion can break output
lines up so that lines break at seemingly random places.
Thus, if you can express the last few characters of a prompt
when writing patterns, it is wise to do so.
If you are waiting for a pattern in the last output of a
program and the program emits something else instead, you
will not be able to detect that with the timeout keyword.
The reason is that expect will not timeout - instead it will
get an eof indication. Use that instead. Even better, use
both. That way if that line is ever moved around, you won't
have to edit the line itself.
Newlines are usually converted to carriage return, linefeed
sequences when output by the terminal driver. Thus, if you
want a pattern that explicitly matches the two lines, from,
say, printf("foo\nbar"), you should use the pattern
"foo\r\nbar".
A similar translation occurs when reading from the user, via
expect_user. In this case, when you press return, it will
be translated to a newline. If Expect then passes that to a
program which sets its terminal to raw mode (like telnet),
there is going to be a problem, as the program expects a
true return. (Some programs are actually forgiving in that
they will automatically translate newlines to returns, but
most don't.) Unfortunately, there is no way to find out
that a program put its terminal into raw mode.
Rather than manually replacing newlines with returns, the
solution is to use the command "stty raw", which will stop
the translation. Note, however, that this means that you
will no longer get the cooked line-editing features.
interact implicitly sets your terminal to raw mode so this
problem will not arise then.
It is often useful to store passwords (or other private
information) in Expect scripts. This is not recommended
since anything that is stored on a computer is susceptible
to being accessed by anyone. Thus, interactively prompting
for passwords from a script is a smarter idea than embedding
them literally. Nonetheless, sometimes such embedding is
the only possibility.
Unfortunately, the UNIX file system has no direct way of
creating scripts which are executable but unreadable. Sys-
tems which support setgid shell scripts may indirectly simu-
late this as follows:
Create the Expect script (that contains the secret data) as
usual. Make its permissions be 750 (-rwxr-x---) and owned
by a trusted group, i.e., a group which is allowed to read
it. If necessary, create a new group for this purpose.
Next, create a /bin/sh script with permissions 2751
(-rwxr-s--x) owned by the same group as before.
The result is a script which may be executed (and read) by
anyone. When invoked, it runs the Expect script.
SEE ALSO
Tcl(3), libexpect(3)
"Exploring Expect: A Tcl-Based Toolkit for Automating
Interactive Programs" by Don Libes, pp. 602, ISBN 1-56592-
090-2, O'Reilly and Associates, 1995.
"expect: Curing Those Uncontrollable Fits of Interactivity"
by Don Libes, Proceedings of the Summer 1990 USENIX Confer-
ence, Anaheim, California, June 11-15, 1990.
"Using expect to Automate System Administration Tasks" by
Don Libes, Proceedings of the 1990 USENIX Large Installation
Systems Administration Conference, Colorado Springs,
Colorado, October 17-19, 1990.
"Tcl: An Embeddable Command Language" by John Ousterhout,
Proceedings of the Winter 1990 USENIX Conference,
Washington, D.C., January 22-26, 1990.
"expect: Scripts for Controlling Interactive Programs" by
Don Libes, Computing Systems, Vol. 4, No. 2, University of
California Press Journals, November 1991.
"Regression Testing and Conformance Testing Interactive Pro-
grams", by Don Libes, Proceedings of the Summer 1992 USENIX
Conference, pp. 135-144, San Antonio, TX, June 12-15, 1992.
"Kibitz - Connecting Multiple Interactive Programs
Together", by Don Libes, Software - Practice & Experience,
John Wiley & Sons, West Sussex, England, Vol. 23, No. 5,
May, 1993.
"A Debugger for Tcl Applications", by Don Libes, Proceedings
of the 1993 Tcl/Tk Workshop, Berkeley, CA, June 10-11, 1993.
AUTHOR
Don Libes, National Institute of Standards and Technology
ACKNOWLEDGMENTS
Thanks to John Ousterhout for Tcl, and Scott Paisley for
inspiration. Thanks to Rob Savoye for Expect's autoconfi-
guration 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 pro-
gram and documentation or portions of them are used.
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