expect - programmed dialogue with interactive programs, Version 5
expect [
-dDinN ] [
-c cmds ] [ [
-[
f|
b] ]
cmdfile ] [
args ]
Expect is a program that "talks" to other interactive programs
according to a script. Following the script,
Expect knows what can be
expected from a program and what the correct response should be. An
interpreted language provides branching and high-level control structures to
direct the dialogue. In addition, the user can take control and interact
directly when desired, afterward returning control to the script.
Expectk is a mixture of
Expect and
Tk. It behaves just like
Expect and
Tk's
wish.
Expect can also be used
directly in C or C++ (that is, without Tcl). See libexpect(3).
The name "Expect" comes from the idea of
send/expect sequences
popularized by uucp, kermit and other modem control programs. However unlike
uucp,
Expect is generalized so that it can be run as a user-level
command with any program and task in mind.
Expect can actually talk to
several programs at the same time.
For example, here are some things
Expect can do:
- •
- Cause your computer to dial you back, so that you can login without paying
for the call.
- •
- Start a game (e.g., rogue) and if the optimal configuration doesn't
appear, restart it (again and again) until it does, then hand over control
to you.
- •
- Run fsck, and in response to its questions, answer "yes",
"no" or give control back to you, based on predetermined
criteria.
- •
- Connect to another network or BBS (e.g., MCI Mail, CompuServe) and
automatically retrieve your mail so that it appears as if it was
originally sent to your local system.
- •
- Carry environment variables, current directory, or any kind of information
across rlogin, telnet, tip, su, chgrp, etc.
There are a variety of reasons why the shell cannot perform these tasks. (Try,
you'll see.) All are possible with
Expect.
In general,
Expect is useful for running any program which requires
interaction between the program and the user. All that is necessary is that
the interaction can be characterized programmatically.
Expect can also
give the user back control (without halting the program being controlled) if
desired. Similarly, the user can return control to the script at any time.
Expect reads
cmdfile for a list of commands to execute.
Expect may also be invoked implicitly on systems which support the #!
notation by marking the script executable, and making the first line in your
script:
#!/usr/local/bin/expect -f
Of course, the path must accurately describe where
Expect lives.
/usr/local/bin is just an example.
The
-c flag prefaces a command to be executed before any in the script.
The command should be quoted to prevent being broken up by the shell. This
option may be used multiple times. Multiple commands may be executed with a
single
-c by separating them with semicolons. Commands are executed in
the order they appear. (When using Expectk, this option is specified as
-command.)
The
-d flag enables some diagnostic output, which primarily reports
internal activity of commands such as
expect and
interact. This
flag has the same effect as "exp_internal 1" at the beginning of an
Expect script, plus the version of
Expect is printed. (The
strace command is useful for tracing statements, and the
trace
command is useful for tracing variable assignments.) (When using Expectk, this
option is specified as
-diag.)
The
-D flag enables an interactive debugger. An integer value should
follow. The debugger will take control before the next Tcl procedure if the
value is non-zero or if a ^C is pressed (or a breakpoint is hit, or other
appropriate debugger command appears in the script). See the README file or
SEE ALSO (below) for more information on the debugger. (When using Expectk,
this option is specified as
-Debug.)
The
-f flag prefaces a file from which to read commands from. The flag
itself is optional as it is only useful when using the #! notation (see
above), so that other arguments may be supplied on the command line. (When
using Expectk, this option is specified as
-file.)
By default, the command file is read into memory and executed in its entirety.
It is occasionally desirable to read files one line at a time. For example,
stdin is read this way. In order to force arbitrary files to be handled this
way, use the
-b flag. (When using Expectk, this option is specified as
-buffer.) Note that stdio-buffering may still take place however this
shouldn't cause problems when reading from a fifo or stdin.
If the string "-" is supplied as a filename, standard input is read
instead. (Use "./-" to read from a file actually named
"-".)
The
-i flag causes
Expect to interactively prompt for commands
instead of reading them from a file. Prompting is terminated via the
exit command or upon EOF. See
interpreter (below) for more
information.
-i is assumed if neither a command file nor
-c is
used. (When using Expectk, this option is specified as
-interactive.)
-- may be used to delimit the end of the options. This is useful if you
want to pass an option-like argument to your script without it being
interpreted by
Expect. This can usefully be placed in the #! line to
prevent any flag-like interpretation by Expect. For example, the following
will leave the original arguments (including the script name) in the variable
argv.
#!/usr/local/bin/expect --
Note that the usual getopt(3) and execve(2) conventions must be observed when
adding arguments to the #! line.
The file $exp_library/expect.rc is sourced automatically if present, unless the
-N flag is used. (When using Expectk, this option is specified as
-NORC.) Immediately after this, the file ~/.expect.rc is sourced
automatically, unless the
-n flag is used. If the environment variable
DOTDIR is defined, it is treated as a directory and .expect.rc is read from
there. (When using Expectk, this option is specified as
-norc.) This
sourcing occurs only after executing any
-c flags.
-v causes Expect to print its version number and exit. (The corresponding
flag in Expectk, which uses long flag names, is -version.)
Optional
args are constructed into a list and stored in the variable
named
argv.
argc is initialized to the length of argv.
argv0 is defined to be the name of the script (or binary if no script is
used). For example, the following prints out the name of the script and the
first three arguments:
send_user "$argv0 [lrange $argv 0 2]\n"
Expect uses
Tcl (Tool Command Language). Tcl provides control flow
(e.g., if, for, break), expression evaluation and several other features such
as recursion, procedure definition, etc. Commands used here but not defined
(e.g.,
set,
if,
exec) are Tcl commands (see tcl(3)).
Expect supports additional commands, described below. Unless otherwise
specified, commands return the empty string.
Commands are listed alphabetically so that they can be quickly located. However,
new users may find it easier to start by reading the descriptions of
spawn,
send,
expect, and
interact, in that order.
Note that the best introduction to the language (both Expect and Tcl) is
provided in the book "Exploring Expect" (see SEE ALSO below).
Examples are included in this man page but they are very limited since this
man page is meant primarily as reference material.
Note that in the text of this man page, "Expect" with an uppercase
"E" refers to the
Expect program while "expect"
with a lower-case "e" refers to the
expect command within the
Expect program.)
- close [-slave] [-onexec 0|1] [-i spawn_id]
- closes the connection to the current process. Most interactive programs
will detect EOF on their stdin and exit; thus close usually
suffices to kill the process as well. The -i flag declares the
process to close corresponding to the named spawn_id.
Both expect and interact will detect when the current process
exits and implicitly do a close. But if you kill the process by,
say, "exec kill $pid", you will need to explicitly call
close.
The -onexec flag determines whether the spawn id will be closed in
any new spawned processes or if the process is overlayed. To leave a spawn
id open, use the value 0. A non-zero integer value will force the spawn
closed (the default) in any new processes.
The -slave flag closes the slave associated with the spawn id. (See
"spawn -pty".) When the connection is closed, the slave is
automatically closed as well if still open.
No matter whether the connection is closed implicitly or explicitly, you
should call wait to clear up the corresponding kernel process slot.
close does not call wait since there is no guarantee that
closing a process connection will cause it to exit. See wait below
for more info.
- debug [[-now] 0|1]
- controls a Tcl debugger allowing you to step through statements, set
breakpoints, etc.
With no arguments, a 1 is returned if the debugger is not running, otherwise
a 0 is returned.
With a 1 argument, the debugger is started. With a 0 argument, the debugger
is stopped. If a 1 argument is preceded by the -now flag, the
debugger is started immediately (i.e., in the middle of the debug
command itself). Otherwise, the debugger is started with the next Tcl
statement.
The debug command does not change any traps. Compare this to starting
Expect with the -D flag (see above).
See the README file or SEE ALSO (below) for more information on the
debugger.
- disconnect
- disconnects a forked process from the terminal. It continues running in
the background. The process is given its own process group (if possible).
Standard I/O is redirected to /dev/null.
- The following fragment uses disconnect to continue running the
script in the background.
if {[fork]!=0} exit
disconnect
. . .
The following script reads a password, and then runs a program every hour
that demands a password each time it is run. The script supplies the
password so that you only have to type it once. (See the stty
command which demonstrates how to turn off password echoing.)
send_user "password?\ "
expect_user -re "(.*)\n"
for {} 1 {} {
if {[fork]!=0} {sleep 3600;continue}
disconnect
spawn priv_prog
expect Password:
send "$expect_out(1,string)\r"
. . .
exit
}
An advantage to using disconnect over the shell asynchronous process
feature (&) is that Expect can save the terminal parameters
prior to disconnection, and then later apply them to new ptys. With &,
Expect does not have a chance to read the terminal's parameters
since the terminal is already disconnected by the time Expect
receives control.
- exit [-opts] [status]
- causes Expect to exit or otherwise prepare to do so.
The -onexit flag causes the next argument to be used as an exit
handler. Without an argument, the current exit handler is returned.
The -noexit flag causes Expect to prepare to exit but stop
short of actually returning control to the operating system. The
user-defined exit handler is run as well as Expect's own internal
handlers. No further Expect commands should be executed. This is useful if
you are running Expect with other Tcl extensions. The current interpreter
(and main window if in the Tk environment) remain so that other Tcl
extensions can clean up. If Expect's exit is called again (however
this might occur), the handlers are not rerun.
Upon exiting, all connections to spawned processes are closed. Closure will
be detected as an EOF by spawned processes. exit takes no other
actions beyond what the normal _exit(2) procedure does. Thus, spawned
processes that do not check for EOF may continue to run. (A variety of
conditions are important to determining, for example, what signals a
spawned process will be sent, but these are system-dependent, typically
documented under exit(3).) Spawned processes that continue to run will be
inherited by init.
status (or 0 if not specified) is returned as the exit status of
Expect. exit is implicitly executed if the end of the script
is reached.
- exp_continue [-continue_timer]
- The command exp_continue allows expect itself to continue
executing rather than returning as it normally would. By default
exp_continue resets the timeout timer. The -continue_timer
flag prevents timer from being restarted. (See expect for more
information.)
- exp_internal [-f file] value
- causes further commands to send diagnostic information internal to
Expect to stderr if value is non-zero. This output is
disabled if value is 0. The diagnostic information includes every
character received, and every attempt made to match the current output
against the patterns.
- If the optional file is supplied, all normal and debugging output
is written to that file (regardless of the value of value). Any
previous diagnostic output file is closed.
The -info flag causes exp_internal to return a description of the
most recent non-info arguments given.
- exp_open [args] [-i spawn_id]
- returns a Tcl file identifier that corresponds to the original spawn id.
The file identifier can then be used as if it were opened by Tcl's
open command. (The spawn id should no longer be used. A wait
should not be executed.
The -leaveopen flag leaves the spawn id open for access through
Expect commands. A wait must be executed on the spawn id.
- exp_pid [-i spawn_id]
- returns the process id corresponding to the currently spawned process. If
the -i flag is used, the pid returned corresponds to that of the
given spawn id.
- exp_send
- is an alias for send.
- exp_send_error
- is an alias for send_error.
- exp_send_log
- is an alias for send_log.
- exp_send_tty
- is an alias for send_tty.
- exp_send_user
- is an alias for send_user.
- exp_version [[-exit] version]
- is useful for assuring that the script is compatible with the current
version of Expect.
- With no arguments, the current version of Expect is returned. This
version may then be encoded in your script. If you actually know that you
are not using features of recent versions, you can specify an earlier
version.
- Versions consist of three numbers separated by dots. First is the major
number. Scripts written for versions of Expect with a different
major number will almost certainly not work. exp_version returns an
error if the major numbers do not match.
- Second is the minor number. Scripts written for a version with a greater
minor number than the current version may depend upon some new feature and
might not run. exp_version returns an error if the major numbers
match, but the script minor number is greater than that of the running
Expect.
- Third is a number that plays no part in the version comparison. However,
it is incremented when the Expect software distribution is changed
in any way, such as by additional documentation or optimization. It is
reset to 0 upon each new minor version.
- With the -exit flag, Expect prints an error and exits if the
version is out of date.
- expect [[-opts] pat1 body1] ... [-opts] patn [bodyn]
- waits until one of the patterns matches the output of a spawned process, a
specified time period has passed, or an end-of-file is seen. If the final
body is empty, it may be omitted.
- Patterns from the most recent expect_before command are implicitly
used before any other patterns. Patterns from the most recent
expect_after command are implicitly used after any other
patterns.
- If the arguments to the entire expect statement require more than
one line, all the arguments may be "braced" into one so as to
avoid terminating each line with a backslash. In this one case, the usual
Tcl substitutions will occur despite the braces.
- If a pattern is the keyword eof, the corresponding body is executed
upon end-of-file. If a pattern is the keyword timeout, the
corresponding body is executed upon timeout. If no timeout keyword is
used, an implicit null action is executed upon timeout. The default
timeout period is 10 seconds but may be set, for example to 30, by the
command "set timeout 30". An infinite timeout may be designated
by the value -1. If a pattern is the keyword default, the
corresponding body is executed upon either timeout or end-of-file.
- If a pattern matches, then the corresponding body is executed.
expect returns the result of the body (or the empty string if no
pattern matched). In the event that multiple patterns match, the one
appearing first is used to select a body.
- Each time new output arrives, it is compared to each pattern in the order
they are listed. Thus, you may test for absence of a match by making the
last pattern something guaranteed to appear, such as a prompt. In
situations where there is no prompt, you must use timeout (just
like you would if you were interacting manually).
- Patterns are specified in three ways. By default, patterns are specified
as with Tcl's string match command. (Such patterns are also similar
to C-shell regular expressions usually referred to as "glob"
patterns). The -gl flag may may be used to protect patterns that
might otherwise match expect flags from doing so. Any pattern
beginning with a "-" should be protected this way. (All strings
starting with "-" are reserved for future options.)
- For example, the following fragment looks for a successful login. (Note
that abort is presumed to be a procedure defined elsewhere in the
script.)
expect {
busy {puts busy\n ; exp_continue}
failed abort
"invalid password" abort
timeout abort
connected
}
Quotes are necessary on the fourth pattern since it contains a space, which
would otherwise separate the pattern from the action. Patterns with the
same action (such as the 3rd and 4th) require listing the actions again.
This can be avoid by using regexp-style patterns (see below). More
information on forming glob-style patterns can be found in the Tcl
manual.
- Regexp-style patterns follow the syntax defined by Tcl's regexp
(short for "regular expression") command. regexp patterns are
introduced with the flag -re. The previous example can be rewritten
using a regexp as:
expect {
busy {puts busy\n ; exp_continue}
-re "failed|invalid password" abort
timeout abort
connected
}
Both types of patterns are "unanchored". This means that patterns
do not have to match the entire string, but can begin and end the match
anywhere in the string (as long as everything else matches). Use ^ to
match the beginning of a string, and $ to match the end. Note that if you
do not wait for the end of a string, your responses can easily end up in
the middle of the string as they are echoed from the spawned process.
While still producing correct results, the output can look unnatural.
Thus, use of $ is encouraged if you can exactly describe the characters at
the end of a string.
Note that in many editors, the ^ and $ match the beginning and end of lines
respectively. However, because expect is not line oriented, these
characters match the beginning and end of the data (as opposed to lines)
currently in the expect matching buffer. (Also, see the note below on
"system indigestion.")
The -ex flag causes the pattern to be matched as an "exact"
string. No interpretation of *, ^, etc is made (although the usual Tcl
conventions must still be observed). Exact patterns are always unanchored.
- The -nocase flag causes uppercase characters of the output to
compare as if they were lowercase characters. The pattern is not
affected.
- While reading output, more than 2000 bytes can force earlier bytes to be
"forgotten". This may be changed with the function
match_max. (Note that excessively large values can slow down the
pattern matcher.) If patlist is full_buffer, the
corresponding body is executed if match_max bytes have been
received and no other patterns have matched. Whether or not the
full_buffer keyword is used, the forgotten characters are written
to expect_out(buffer).
If patlist is the keyword null, and nulls are allowed (via the
remove_nulls command), the corresponding body is executed if a
single ASCII 0 is matched. It is not possible to match 0 bytes via glob or
regexp patterns.
Upon matching a pattern (or eof or full_buffer), any matching and previously
unmatched output is saved in the variable expect_out(buffer). Up to
9 regexp substring matches are saved in the variables
expect_out(1,string) through expect_out(9,string). If the
-indices flag is used before a pattern, the starting and ending
indices (in a form suitable for lrange) of the 10 strings are
stored in the variables expect_out(X,start) and
expect_out(X,end) where X is a digit, corresponds to the substring
position in the buffer. 0 refers to strings which matched the entire
pattern and is generated for glob patterns as well as regexp patterns. For
example, if a process has produced output of "abcdefgh\n", the
result of:
expect "cd"
is as if the following statements had executed:
set expect_out(0,string) cd
set expect_out(buffer) abcd
and "efgh\n" is left in the output buffer. If a process produced
the output "abbbcabkkkka\n", the result of:
expect -indices -re "b(b*).*(k+)"
is as if the following statements had executed:
set expect_out(0,start) 1
set expect_out(0,end) 10
set expect_out(0,string) bbbcabkkkk
set expect_out(1,start) 2
set expect_out(1,end) 3
set expect_out(1,string) bb
set expect_out(2,start) 10
set expect_out(2,end) 10
set expect_out(2,string) k
set expect_out(buffer) abbbcabkkkk
and "a\n" is left in the output buffer. The pattern "*"
(and -re ".*") will flush the output buffer without reading any
more output from the process.
- Normally, the matched output is discarded from Expect's internal buffers.
This may be prevented by prefixing a pattern with the -notransfer
flag. This flag is especially useful in experimenting (and can be
abbreviated to "-not" for convenience while experimenting).
The spawn id associated with the matching output (or eof or full_buffer) is
stored in expect_out(spawn_id).
The -timeout flag causes the current expect command to use the
following value as a timeout instead of using the value of the timeout
variable.
By default, patterns are matched against output from the current process,
however the -i flag declares the output from the named spawn_id
list be matched against any following patterns (up to the next -i).
The spawn_id list should either be a whitespace separated list of
spawn_ids or a variable referring to such a list of spawn_ids.
For example, the following example waits for "connected" from the
current process, or "busy", "failed" or "invalid
password" from the spawn_id named by $proc2.
expect {
-i $proc2 busy {puts busy\n ; exp_continue}
-re "failed|invalid password" abort
timeout abort
connected
}
The value of the global variable any_spawn_id may be used to match
patterns to any spawn_ids that are named with all other -i flags in
the current expect command. The spawn_id from a -i flag with
no associated pattern (i.e., followed immediately by another -i) is
made available to any other patterns in the same expect command
associated with any_spawn_id.
The -i flag may also name a global variable in which case the
variable is read for a list of spawn ids. The variable is reread whenever
it changes. This provides a way of changing the I/O source while the
command is in execution. Spawn ids provided this way are called
"indirect" spawn ids.
Actions such as break and continue cause control structures
(i.e., for, proc) to behave in the usual way. The command
exp_continue allows expect itself to continue executing
rather than returning as it normally would.
- This is useful for avoiding explicit loops or repeated expect statements.
The following example is part of a fragment to automate rlogin. The
exp_continue avoids having to write a second expect
statement (to look for the prompt again) if the rlogin prompts for a
password.
expect {
Password: {
stty -echo
send_user "password (for $user) on $host: "
expect_user -re "(.*)\n"
send_user "\n"
send "$expect_out(1,string)\r"
stty echo
exp_continue
} incorrect {
send_user "invalid password or account\n"
exit
} timeout {
send_user "connection to $host timed out\n"
exit
} eof {
send_user \
"connection to host failed: $expect_out(buffer)"
exit
} -re $prompt
}
For example, the following fragment might help a user guide an interaction
that is already totally automated. In this case, the terminal is put into
raw mode. If the user presses "+", a variable is incremented. If
"p" is pressed, several returns are sent to the process, perhaps
to poke it in some way, and "i" lets the user interact with the
process, effectively stealing away control from the script. In each case,
the exp_continue allows the current expect to continue
pattern matching after executing the current action.
stty raw -echo
expect_after {
-i $user_spawn_id
"p" {send "\r\r\r"; exp_continue}
"+" {incr foo; exp_continue}
"i" {interact; exp_continue}
"quit" exit
}
- By default, exp_continue resets the timeout timer. The timer is not
restarted, if exp_continue is called with the
-continue_timer flag.
- expect_after [expect_args]
- works identically to the expect_before except that if patterns from
both expect and expect_after can match, the expect
pattern is used. See the expect_before command for more
information.
- expect_background [expect_args]
- takes the same arguments as expect, however it returns immediately.
Patterns are tested whenever new input arrives. The pattern timeout
and default are meaningless to expect_background and are
silently discarded. Otherwise, the expect_background command uses
expect_before and expect_after patterns just like
expect does.
When expect_background actions are being evaluated, background
processing for the same spawn id is blocked. Background processing is
unblocked when the action completes. While background processing is
blocked, it is possible to do a (foreground) expect on the same
spawn id.
It is not possible to execute an expect while an
expect_background is unblocked. expect_background for a
particular spawn id is deleted by declaring a new expect_background with
the same spawn id. Declaring expect_background with no pattern
removes the given spawn id from the ability to match patterns in the
background.
- expect_before [expect_args]
- takes the same arguments as expect, however it returns immediately.
Pattern-action pairs from the most recent expect_before with the
same spawn id are implicitly added to any following expect
commands. If a pattern matches, it is treated as if it had been specified
in the expect command itself, and the associated body is executed
in the context of the expect command. If patterns from both
expect_before and expect can match, the expect_before
pattern is used.
If no pattern is specified, the spawn id is not checked for any patterns.
Unless overridden by a -i flag, expect_before patterns match
against the spawn id defined at the time that the expect_before
command was executed (not when its pattern is matched).
The -info flag causes expect_before to return the current
specifications of what patterns it will match. By default, it reports on
the current spawn id. An optional spawn id specification may be given for
information on that spawn id. For example
expect_before -info -i $proc
At most one spawn id specification may be given. The flag -indirect
suppresses direct spawn ids that come only from indirect specifications.
Instead of a spawn id specification, the flag "-all" will cause
"-info" to report on all spawn ids.
The output of the -info flag can be reused as the argument to
expect_before.
- expect_tty [expect_args]
- is like expect but it reads characters from /dev/tty (i.e.
keystrokes from the user). By default, reading is performed in cooked
mode. Thus, lines must end with a return in order for expect to see
them. This may be changed via stty (see the stty command
below).
- expect_user [expect_args]
- is like expect but it reads characters from stdin (i.e. keystrokes
from the user). By default, reading is performed in cooked mode. Thus,
lines must end with a return in order for expect to see them. This
may be changed via stty (see the stty command below).
- fork
- creates a new process. The new process is an exact copy of the current
Expect process. On success, fork returns 0 to the new
(child) process and returns the process ID of the child process to the
parent process. On failure (invariably due to lack of resources, e.g.,
swap space, memory), fork returns -1 to the parent process, and no
child process is created.
- Forked processes exit via the exit command, just like the original
process. Forked processes are allowed to write to the log files. If you do
not disable debugging or logging in most of the processes, the result can
be confusing.
- Some pty implementations may be confused by multiple readers and writers,
even momentarily. Thus, it is safest to fork before spawning
processes.
- interact [string1 body1] ... [stringn [bodyn]]
- gives control of the current process to the user, so that keystrokes are
sent to the current process, and the stdout and stderr of the current
process are returned.
- String-body pairs may be specified as arguments, in which case the body is
executed when the corresponding string is entered. (By default, the string
is not sent to the current process.) The interpreter command is
assumed, if the final body is missing.
- If the arguments to the entire interact statement require more than
one line, all the arguments may be "braced" into one so as to
avoid terminating each line with a backslash. In this one case, the usual
Tcl substitutions will occur despite the braces.
- For example, the following command runs interact with the following
string-body pairs defined: When ^Z is pressed, Expect is suspended.
(The -reset flag restores the terminal modes.) When ^A is pressed,
the user sees "you typed a control-A" and the process is sent a
^A. When $ is pressed, the user sees the date. When ^C is pressed,
Expect exits. If "foo" is entered, the user sees
"bar". When ~~ is pressed, the Expect interpreter runs
interactively.
set CTRLZ \032
interact {
-reset $CTRLZ {exec kill -STOP [pid]}
\001 {send_user "you typed a control-A\n";
send "\001"
}
$ {send_user "The date is [clock format [clock seconds]]."}
\003 exit
foo {send_user "bar"}
~~
}
- In string-body pairs, strings are matched in the order they are listed as
arguments. Strings that partially match are not sent to the current
process in anticipation of the remainder coming. If characters are then
entered such that there can no longer possibly be a match, only the part
of the string will be sent to the process that cannot possibly begin
another match. Thus, strings that are substrings of partial matches can
match later, if the original strings that was attempting to be match
ultimately fails.
- By default, string matching is exact with no wild cards. (In contrast, the
expect command uses glob-style patterns by default.) The -ex
flag may be used to protect patterns that might otherwise match
interact flags from doing so. Any pattern beginning with a
"-" should be protected this way. (All strings starting with
"-" are reserved for future options.)
The -re flag forces the string to be interpreted as a regexp-style
pattern. In this case, matching substrings are stored in the variable
interact_out similarly to the way expect stores its output
in the variable expect_out. The -indices flag is similarly
supported.
The pattern eof introduces an action that is executed upon
end-of-file. A separate eof pattern may also follow the
-output flag in which case it is matched if an eof is detected
while writing output. The default eof action is "return",
so that interact simply returns upon any EOF.
The pattern timeout introduces a timeout (in seconds) and action that
is executed after no characters have been read for a given time. The
timeout pattern applies to the most recently specified process.
There is no default timeout. The special variable "timeout"
(used by the expect command) has no affect on this timeout.
For example, the following statement could be used to autologout users who
have not typed anything for an hour but who still get frequent system
messages:
interact -input $user_spawn_id timeout 3600 return -output \
$spawn_id
If the pattern is the keyword null, and nulls are allowed (via the
remove_nulls command), the corresponding body is executed if a
single ASCII 0 is matched. It is not possible to match 0 bytes via glob or
regexp patterns.
Prefacing a pattern with the flag -iwrite causes the variable
interact_out(spawn_id) to be set to the spawn_id which matched the
pattern (or eof).
Actions such as break and continue cause control structures
(i.e., for, proc) to behave in the usual way. However
return causes interact to return to its caller, while
inter_return causes interact to cause a return in its
caller. For example, if "proc foo" called interact which
then executed the action inter_return, proc foo would
return. (This means that if interact calls interpreter
interactively typing return will cause the interact to continue,
while inter_return will cause the interact to return to its
caller.)
- During interact, raw mode is used so that all characters may be
passed to the current process. If the current process does not catch job
control signals, it will stop if sent a stop signal (by default ^Z). To
restart it, send a continue signal (such as by "kill -CONT
<pid>"). If you really want to send a SIGSTOP to such a process
(by ^Z), consider spawning csh first and then running your program. On the
other hand, if you want to send a SIGSTOP to Expect itself, first
call interpreter (perhaps by using an escape character), and then press
^Z.
- String-body pairs can be used as a shorthand for avoiding having to enter
the interpreter and execute commands interactively. The previous terminal
mode is used while the body of a string-body pair is being executed.
- For speed, actions execute in raw mode by default. The -reset flag
resets the terminal to the mode it had before interact was executed
(invariably, cooked mode). Note that characters entered when the mode is
being switched may be lost (an unfortunate feature of the terminal driver
on some systems). The only reason to use -reset is if your action
depends on running in cooked mode.
- The -echo flag sends characters that match the following pattern
back to the process that generated them as each character is read. This
may be useful when the user needs to see feedback from partially typed
patterns.
- If a pattern is being echoed but eventually fails to match, the characters
are sent to the spawned process. If the spawned process then echoes them,
the user will see the characters twice. -echo is probably only
appropriate in situations where the user is unlikely to not complete the
pattern. For example, the following excerpt is from rftp, the
recursive-ftp script, where the user is prompted to enter ~g, ~p, or ~l,
to get, put, or list the current directory recursively. These are so far
away from the normal ftp commands, that the user is unlikely to type ~
followed by anything else, except mistakenly, in which case, they'll
probably just ignore the result anyway.
interact {
-echo ~g {getcurdirectory 1}
-echo ~l {getcurdirectory 0}
-echo ~p {putcurdirectory}
}
The -nobuffer flag sends characters that match the following pattern
on to the output process as characters are read.
This is useful when you wish to let a program echo back the pattern. For
example, the following might be used to monitor where a person is dialing
(a Hayes-style modem). Each time "atd" is seen the script logs
the rest of the line.
proc lognumber {} {
interact -nobuffer -re "(.*)\r" return
puts $log "[clock format [clock seconds]]: dialed $interact_out(1,string)"
}
interact -nobuffer "atd" lognumber
- During interact, previous use of log_user is ignored. In
particular, interact will force its output to be logged (sent to
the standard output) since it is presumed the user doesn't wish to
interact blindly.
- The -o flag causes any following key-body pairs to be applied to
the output of the current process. This can be useful, for example, when
dealing with hosts that send unwanted characters during a telnet
session.
- By default, interact expects the user to be writing stdin and
reading stdout of the Expect process itself. The -u flag
(for "user") makes interact look for the user as the
process named by its argument (which must be a spawned id).
- This allows two unrelated processes to be joined together without using an
explicit loop. To aid in debugging, Expect diagnostics always go to stderr
(or stdout for certain logging and debugging information). For the same
reason, the interpreter command will read interactively from
stdin.
- For example, the following fragment creates a login process. Then it dials
the user (not shown), and finally connects the two together. Of course,
any process may be substituted for login. A shell, for example, would
allow the user to work without supplying an account and password.
spawn login
set login $spawn_id
spawn tip modem
# dial back out to user
# connect user to login
interact -u $login
To send output to multiple processes, list each spawn id list prefaced by a
-output flag. Input for a group of output spawn ids may be
determined by a spawn id list prefaced by a -input flag. (Both
-input and -output may take lists in the same form as the
-i flag in the expect command, except that any_spawn_id is
not meaningful in interact.) All following flags and strings (or
patterns) apply to this input until another -input flag appears. If no
-input appears, -output implies "-input $user_spawn_id
-output". (Similarly, with patterns that do not have -input.)
If one -input is specified, it overrides $user_spawn_id. If a
second -input is specified, it overrides $spawn_id. Additional
-input flags may be specified.
The two implied input processes default to having their outputs specified as
$spawn_id and $user_spawn_id (in reverse). If a -input flag appears
with no -output flag, characters from that process are discarded.
The -i flag introduces a replacement for the current spawn_id when no
other -input or -output flags are used. A -i flag implies a
-o flag.
It is possible to change the processes that are being interacted with by
using indirect spawn ids. (Indirect spawn ids are described in the section
on the expect command.) Indirect spawn ids may be specified with the -i,
-u, -input, or -output flags.
- interpreter [args]
- causes the user to be interactively prompted for Expect and Tcl
commands. The result of each command is printed.
- Actions such as break and continue cause control structures
(i.e., for, proc) to behave in the usual way. However
return causes interpreter to return to its caller, while
inter_return causes interpreter to cause a return in its
caller. For example, if "proc foo" called interpreter
which then executed the action inter_return, proc foo would
return. Any other command causes interpreter to continue prompting
for new commands.
- By default, the prompt contains two integers. The first integer describes
the depth of the evaluation stack (i.e., how many times Tcl_Eval has been
called). The second integer is the Tcl history identifier. The prompt can
be set by defining a procedure called "prompt1" whose return
value becomes the next prompt. If a statement has open quotes, parens,
braces, or brackets, a secondary prompt (by default "+> ") is
issued upon newline. The secondary prompt may be set by defining a
procedure called "prompt2".
- During interpreter, cooked mode is used, even if the its caller was
using raw mode.
- If stdin is closed, interpreter will return unless the -eof
flag is used, in which case the subsequent argument is invoked.
- log_file [args] [[-a] file]
- If a filename is provided, log_file will record a transcript of the
session (beginning at that point) in the file. log_file will stop
recording if no argument is given. Any previous log file is closed.
Instead of a filename, a Tcl file identifier may be provided by using the
-open or -leaveopen flags. This is similar to the
spawn command. (See spawn for more info.)
The -a flag forces output to be logged that was suppressed by the
log_user command.
By default, the log_file command appends to old files rather
than truncating them, for the convenience of being able to turn logging
off and on multiple times in one session. To truncate files, use the
-noappend flag.
The -info flag causes log_file to return a description of the most
recent non-info arguments given.
- log_user -info|0|1
- By default, the send/expect dialogue is logged to stdout (and a logfile if
open). The logging to stdout is disabled by the command "log_user
0" and reenabled by "log_user 1". Logging to the logfile is
unchanged.
The -info flag causes log_user to return a description of the most
recent non-info arguments given.
- match_max [-d] [-i spawn_id] [size]
- defines the size of the buffer (in bytes) used internally by
expect. With no size argument, the current size is
returned.
- With the -d flag, the default size is set. (The initial default is
2000.) With the -i flag, the size is set for the named spawn id,
otherwise it is set for the current process.
- overlay [-# spawn_id] [-# spawn_id] [...] program
[args]
- executes program args in place of the current Expect
program, which terminates. A bare hyphen argument forces a hyphen in front
of the command name as if it was a login shell. All spawn_ids are closed
except for those named as arguments. These are mapped onto the named file
identifiers.
- Spawn_ids are mapped to file identifiers for the new program to inherit.
For example, the following line runs chess and allows it to be controlled
by the current process - say, a chess master.
overlay -0 $spawn_id -1 $spawn_id -2 $spawn_id chess
This is more efficient than "interact -u", however, it sacrifices
the ability to do programmed interaction since the Expect process
is no longer in control.
- Note that no controlling terminal is provided. Thus, if you disconnect or
remap standard input, programs that do job control (shells, login, etc)
will not function properly.
- parity [-d] [-i spawn_id] [value]
- defines whether parity should be retained or stripped from the output of
spawned processes. If value is zero, parity is stripped, otherwise
it is not stripped. With no value argument, the current value is
returned.
- With the -d flag, the default parity value is set. (The initial
default is 1, i.e., parity is not stripped.) With the -i flag, the
parity value is set for the named spawn id, otherwise it is set for the
current process.
- remove_nulls [-d] [-i spawn_id] [value]
- defines whether nulls are retained or removed from the output of spawned
processes before pattern matching or storing in the variable
expect_out or interact_out. If value is 1, nulls are
removed. If value is 0, nulls are not removed. With no value
argument, the current value is returned.
- With the -d flag, the default value is set. (The initial default is
1, i.e., nulls are removed.) With the -i flag, the value is set for
the named spawn id, otherwise it is set for the current process.
Whether or not nulls are removed, Expect will record null bytes to
the log and stdout.
- send [-flags] string
- Sends string to the current process. For example, the command
send "hello world\r"
sends the characters, h e l l o <blank> w o r l d <return> to
the current process. (Tcl includes a printf-like command (called
format) which can build arbitrarily complex strings.)
- Characters are sent immediately although programs with line-buffered input
will not read the characters until a return character is sent. A return
character is denoted "\r".
The -- flag forces the next argument to be interpreted as a string
rather than a flag. Any string can be preceded by "--" whether
or not it actually looks like a flag. This provides a reliable mechanism
to specify variable strings without being tripped up by those that
accidentally look like flags. (All strings starting with "-" are
reserved for future options.)
The -i flag declares that the string be sent to the named spawn_id.
If the spawn_id is user_spawn_id, and the terminal is in raw mode,
newlines in the string are translated to return-newline sequences so that
they appear as if the terminal was in cooked mode. The -raw flag
disables this translation.
The -null flag sends null characters (0 bytes). By default, one null
is sent. An integer may follow the -null to indicate how many nulls
to send.
The -break flag generates a break condition. This only makes sense if
the spawn id refers to a tty device opened via "spawn -open". If
you have spawned a process such as tip, you should use tip's convention
for generating a break.
The -s flag forces output to be sent "slowly", thus avoid
the common situation where a computer outtypes an input buffer that was
designed for a human who would never outtype the same buffer. This output
is controlled by the value of the variable "send_slow" which
takes a two element list. The first element is an integer that describes
the number of bytes to send atomically. The second element is a real
number that describes the number of seconds by which the atomic sends must
be separated. For example, "set send_slow {10 .001}" would force
"send -s" to send strings with 1 millisecond in between each 10
characters sent.
The -h flag forces output to be sent (somewhat) like a human actually
typing. Human-like delays appear between the characters. (The algorithm is
based upon a Weibull distribution, with modifications to suit this
particular application.) This output is controlled by the value of the
variable "send_human" which takes a five element list. The first
two elements are average interarrival time of characters in seconds. The
first is used by default. The second is used at word endings, to simulate
the subtle pauses that occasionally occur at such transitions. The third
parameter is a measure of variability where .1 is quite variable, 1 is
reasonably variable, and 10 is quite invariable. The extremes are 0 to
infinity. The last two parameters are, respectively, a minimum and maximum
interarrival time. The minimum and maximum are used last and
"clip" the final time. The ultimate average can be quite
different from the given average if the minimum and maximum clip enough
values.
As an example, the following command emulates a fast and consistent typist:
set send_human {.1 .3 1 .05 2}
send -h "I'm hungry. Let's do lunch."
while the following might be more suitable after a hangover:
set send_human {.4 .4 .2 .5 100}
send -h "Goodd party lash night!"
Note that errors are not simulated, although you can set up error correction
situations yourself by embedding mistakes and corrections in a send
argument.
The flags for sending null characters, for sending breaks, for forcing slow
output and for human-style output are mutually exclusive. Only the one
specified last will be used. Furthermore, no string argument can be
specified with the flags for sending null characters or breaks.
It is a good idea to precede the first send to a process by an
expect. expect will wait for the process to start, while
send cannot. In particular, if the first send completes
before the process starts running, you run the risk of having your data
ignored. In situations where interactive programs offer no initial prompt,
you can precede send by a delay as in:
# To avoid giving hackers hints on how to break in,
# this system does not prompt for an external password.
# Wait for 5 seconds for exec to complete
spawn telnet very.secure.gov
sleep 5
send password\r
exp_send is an alias for send. If you are using Expectk
or some other variant of Expect in the Tk environment, send is
defined by Tk for an entirely different purpose. exp_send is
provided for compatibility between environments. Similar aliases are
provided for other Expect's other send commands.
- send_error [-flags] string
- is like send, except that the output is sent to stderr rather than
the current process.
- send_log [--] string
- is like send, except that the string is only sent to the log file
(see log_file.) The arguments are ignored if no log file is
open.
- send_tty [-flags] string
- is like send, except that the output is sent to /dev/tty rather
than the current process.
- send_user [-flags] string
- is like send, except that the output is sent to stdout rather than
the current process.
- sleep seconds
- causes the script to sleep for the given number of seconds. Seconds may be
a decimal number. Interrupts (and Tk events if you are using Expectk) are
processed while Expect sleeps.
- spawn [args] program [args]
- creates a new process running program args. Its stdin, stdout and
stderr are connected to Expect, so that they may be read and written by
other Expect commands. The connection is broken by close or
if the process itself closes any of the file identifiers.
- When a process is started by spawn, the variable spawn_id is
set to a descriptor referring to that process. The process described by
spawn_id is considered the current process. spawn_id
may be read or written, in effect providing job control.
- user_spawn_id is a global variable containing a descriptor which
refers to the user. For example, when spawn_id is set to this
value, expect behaves like expect_user.
error_spawn_id is a global variable containing a descriptor which
refers to the standard error. For example, when spawn_id is set to
this value, send behaves like send_error.
- tty_spawn_id is a global variable containing a descriptor which
refers to /dev/tty. If /dev/tty does not exist (such as in a cron, at, or
batch script), then tty_spawn_id is not defined. This may be tested
as:
if {[info vars tty_spawn_id]} {
# /dev/tty exists
} else {
# /dev/tty doesn't exist
# probably in cron, batch, or at script
}
- spawn returns the UNIX process id. If no process is spawned, 0 is
returned. The variable spawn_out(slave,name) is set to the name of
the pty slave device.
- By default, spawn echoes the command name and arguments. The
-noecho flag stops spawn from doing this.
- The -console flag causes console output to be redirected to the
spawned process. This is not supported on all systems.
Internally, spawn uses a pty, initialized the same way as the user's
tty. This is further initialized so that all settings are "sane"
(according to stty(1)). If the variable stty_init is defined, it is
interpreted in the style of stty arguments as further configuration. For
example, "set stty_init raw" will cause further spawned
processes's terminals to start in raw mode. -nottycopy skips the
initialization based on the user's tty. -nottyinit skips the
"sane" initialization.
- Normally, spawn takes little time to execute. If you notice spawn
taking a significant amount of time, it is probably encountering ptys that
are wedged. A number of tests are run on ptys to avoid entanglements with
errant processes. (These take 10 seconds per wedged pty.) Running Expect
with the -d option will show if Expect is encountering many
ptys in odd states. If you cannot kill the processes to which these ptys
are attached, your only recourse may be to reboot.
If program cannot be spawned successfully because exec(2) fails (e.g.
when program doesn't exist), an error message will be returned by
the next interact or expect command as if program had
run and produced the error message as output. This behavior is a natural
consequence of the implementation of spawn. Internally, spawn
forks, after which the spawned process has no way to communicate with the
original Expect process except by communication via the spawn_id.
The -open flag causes the next argument to be interpreted as a Tcl
file identifier (i.e., returned by open.) The spawn id can then be
used as if it were a spawned process. (The file identifier should no
longer be used.) This lets you treat raw devices, files, and pipelines as
spawned processes without using a pty. 0 is returned to indicate there is
no associated process. When the connection to the spawned process is
closed, so is the Tcl file identifier. The -leaveopen flag is
similar to -open except that -leaveopen causes the file
identifier to be left open even after the spawn id is closed.
The -pty flag causes a pty to be opened but no process spawned. 0 is
returned to indicate there is no associated process. Spawn_id is set as
usual.
The variable spawn_out(slave,fd) is set to a file identifier
corresponding to the pty slave. It can be closed using "close
-slave".
The -ignore flag names a signal to be ignored in the spawned process.
Otherwise, signals get the default behavior. Signals are named as in the
trap command, except that each signal requires a separate
flag.
- strace level
- causes following statements to be printed before being executed. (Tcl's
trace command traces variables.) level indicates how far down in
the call stack to trace. For example, the following command runs
Expect while tracing the first 4 levels of calls, but none below
that.
expect -c "strace 4" script.exp
The -info flag causes strace to return a description of the most
recent non-info arguments given.
- stty args
- changes terminal modes similarly to the external stty command.
By default, the controlling terminal is accessed. Other terminals can be
accessed by appending "< /dev/tty..." to the command. (Note
that the arguments should not be grouped into a single argument.)
Requests for status return it as the result of the command. If no status is
requested and the controlling terminal is accessed, the previous status of
the raw and echo attributes are returned in a form which can later be used
by the command.
For example, the arguments raw or -cooked put the terminal
into raw mode. The arguments -raw or cooked put the terminal
into cooked mode. The arguments echo and -echo put the
terminal into echo and noecho mode respectively.
- The following example illustrates how to temporarily disable echoing. This
could be used in otherwise-automatic scripts to avoid embedding passwords
in them. (See more discussion on this under EXPECT HINTS below.)
stty -echo
send_user "Password: "
expect_user -re "(.*)\n"
set password $expect_out(1,string)
stty echo
- system args
- gives args to sh(1) as input, just as if it had been typed as a
command from a terminal. Expect waits until the shell terminates.
The return status from sh is handled the same way that exec handles
its return status.
- In contrast to exec which redirects stdin and stdout to the script,
system performs no redirection (other than that indicated by the
string itself). Thus, it is possible to use programs which must talk
directly to /dev/tty. For the same reason, the results of system
are not recorded in the log.
- timestamp [args]
- returns a timestamp. With no arguments, the number of seconds since the
epoch is returned.
The -format flag introduces a string which is returned but with
substitutions made according to the POSIX rules for strftime. For example
%a is replaced by an abbreviated weekday name (i.e., Sat). Others are:
%a abbreviated weekday name
%A full weekday name
%b abbreviated month name
%B full month name
%c date-time as in: Wed Oct 6 11:45:56 1993
%d day of the month (01-31)
%H hour (00-23)
%I hour (01-12)
%j day (001-366)
%m month (01-12)
%M minute (00-59)
%p am or pm
%S second (00-61)
%u day (1-7, Monday is first day of week)
%U week (00-53, first Sunday is first day of week one)
%V week (01-53, ISO 8601 style)
%w day (0-6)
%W week (00-53, first Monday is first day of week one)
%x date-time as in: Wed Oct 6 1993
%X time as in: 23:59:59
%y year (00-99)
%Y year as in: 1993
%Z timezone (or nothing if not determinable)
%% a bare percent sign
Other % specifications are undefined. Other characters will be passed
through untouched. Only the C locale is supported.
The -seconds flag introduces a number of seconds since the epoch to
be used as a source from which to format. Otherwise, the current time is
used.
The -gmt flag forces timestamp output to use the GMT timezone. With
no flag, the local timezone is used.
- trap [[command] signals]
- causes the given command to be executed upon future receipt of any
of the given signals. The command is executed in the global scope. If
command is absent, the signal action is returned. If command
is the string SIG_IGN, the signals are ignored. If command is the
string SIG_DFL, the signals are result to the system default.
signals is either a single signal or a list of signals. Signals may
be specified numerically or symbolically as per signal(3). The
"SIG" prefix may be omitted.
With no arguments (or the argument -number), trap returns the signal
number of the trap command currently being executed.
The -code flag uses the return code of the command in place of
whatever code Tcl was about to return when the command originally started
running.
The -interp flag causes the command to be evaluated using the
interpreter active at the time the command started running rather than
when the trap was declared.
The -name flag causes the trap command to return the signal
name of the trap command currently being executed.
The -max flag causes the trap command to return the largest
signal number that can be set.
For example, the command "trap {send_user "Ouch!"}
SIGINT" will print "Ouch!" each time the user presses ^C.
By default, SIGINT (which can usually be generated by pressing ^C) and
SIGTERM cause Expect to exit. This is due to the following trap, created
by default when Expect starts.
trap exit {SIGINT SIGTERM}
If you use the -D flag to start the debugger, SIGINT is redefined to start
the interactive debugger. This is due to the following trap:
trap {exp_debug 1} SIGINT
The debugger trap can be changed by setting the environment variable
EXPECT_DEBUG_INIT to a new trap command.
You can, of course, override both of these just by adding trap commands to
your script. In particular, if you have your own "trap exit
SIGINT", this will override the debugger trap. This is useful if you
want to prevent users from getting to the debugger at all.
If you want to define your own trap on SIGINT but still trap to the debugger
when it is running, use:
if {![exp_debug]} {trap mystuff SIGINT}
Alternatively, you can trap to the debugger using some other signal.
trap will not let you override the action for SIGALRM as this is used
internally to Expect. The disconnect command sets SIGALRM to
SIG_IGN (ignore). You can reenable this as long as you disable it during
subsequent spawn commands.
See signal(3) for more info.
- wait [args]
- delays until a spawned process (or the current process if none is named)
terminates.
- wait normally returns a list of four integers. The first integer is
the pid of the process that was waited upon. The second integer is the
corresponding spawn id. The third integer is -1 if an operating system
error occurred, or 0 otherwise. If the third integer was 0, the fourth
integer is the status returned by the spawned process. If the third
integer was -1, the fourth integer is the value of errno set by the
operating system. The global variable errorCode is also set.
Additional elements may appear at the end of the return value from
wait. An optional fifth element identifies a class of information.
Currently, the only possible value for this element is CHILDKILLED in
which case the next two values are the C-style signal name and a short
textual description.
- The -i flag declares the process to wait corresponding to the named
spawn_id (NOT the process id). Inside a SIGCHLD handler, it is possible to
wait for any spawned process by using the spawn id -1.
The -nowait flag causes the wait to return immediately with the
indication of a successful wait. When the process exits (later), it will
automatically disappear without the need for an explicit wait.
The wait command may also be used wait for a forked process using the
arguments "-i -1". Unlike its use with spawned processes, this
command can be executed at any time. There is no control over which
process is reaped. However, the return value can be checked for the
process id.
Expect automatically knows about two built-in libraries for Expect scripts.
These are defined by the directories named in the variables exp_library and
exp_exec_library. Both are meant to contain utility files that can be used by
other scripts.
exp_library contains architecture-independent files. exp_exec_library contains
architecture-dependent files. Depending on your system, both directories may
be totally empty. The existence of the file $exp_exec_library/cat-buffers
describes whether your /bin/cat buffers by default.
A vgrind definition is available for pretty-printing
Expect scripts.
Assuming the vgrind definition supplied with the
Expect distribution is
correctly installed, you can use it as:
vgrind -lexpect file
It many not be apparent how to put everything together that the man page
describes. I encourage you to read and try out the examples in the example
directory of the
Expect distribution. Some of them are real programs.
Others are simply illustrative of certain techniques, and of course, a couple
are just quick hacks. The INSTALL file has a quick overview of these programs.
The
Expect papers (see SEE ALSO) are also useful. While some papers use
syntax corresponding to earlier versions of Expect, the accompanying
rationales are still valid and go into a lot more detail than this man page.
Extensions may collide with Expect's command names. For example,
send is
defined by Tk for an entirely different purpose. For this reason, most of the
Expect commands are also available as "exp_XXXX". Commands
and variables beginning with "exp", "inter",
"spawn", and "timeout" do not have aliases. Use the
extended command names if you need this compatibility between environments.
Expect takes a rather liberal view of scoping. In particular, variables
read by commands specific to the
Expect program will be sought first
from the local scope, and if not found, in the global scope. For example, this
obviates the need to place "global timeout" in every procedure you
write that uses
expect. On the other hand, variables written are always
in the local scope (unless a "global" command has been issued). The
most common problem this causes is when spawn is executed in a procedure.
Outside the procedure,
spawn_id no longer exists, so the spawned
process is no longer accessible simply because of scoping. Add a "global
spawn_id" to such a procedure.
If you cannot enable the multispawning capability (i.e., your system supports
neither select (BSD *.*), poll (SVR>2), nor something equivalent),
Expect will only be able to control a single process at a time. In this
case, do not attempt to set
spawn_id, nor should you execute processes
via exec while a spawned process is running. Furthermore, you will not be able
to
expect from multiple processes (including the user as one) at the
same time.
Terminal parameters can have a big effect on scripts. For example, if a script
is written to look for echoing, it will misbehave if echoing is turned off.
For this reason, Expect forces sane terminal parameters by default.
Unfortunately, this can make things unpleasant for other programs. As an
example, the emacs shell wants to change the "usual" mappings:
newlines get mapped to newlines instead of carriage-return newlines, and
echoing is disabled. This allows one to use emacs to edit the input line.
Unfortunately, Expect cannot possibly guess this.
You can request that Expect not override its default setting of terminal
parameters, but you must then be very careful when writing scripts for such
environments. In the case of emacs, avoid depending upon things like echoing
and end-of-line mappings.
The commands that accepted arguments braced into a single list (the
expect variants and
interact) use a heuristic to decide if the
list is actually one argument or many. The heuristic can fail only in the case
when the list actually does represent a single argument which has multiple
embedded \n's with non-whitespace characters between them. This seems
sufficiently improbable, however the argument "-nobrace" can be used
to force a single argument to be handled as a single argument. This could
conceivably be used with machine-generated Expect code. Similarly, -brace
forces a single argument to be handle as multiple patterns/actions.
It was really tempting to name the program "sex" (for either
"Smart EXec" or "Send-EXpect"), but good sense (or perhaps
just Puritanism) prevailed.
On some systems, when a shell is spawned, it complains about not being able to
access the tty but runs anyway. This means your system has a mechanism for
gaining the controlling tty that
Expect doesn't know about. Please find
out what it is, and send this information back to me.
Ultrix 4.1 (at least the latest versions around here) considers timeouts of
above 1000000 to be equivalent to 0.
Digital UNIX 4.0A (and probably other versions) refuses to allocate ptys if you
define a SIGCHLD handler. See grantpt page for more info.
IRIX 6.0 does not handle pty permissions correctly so that if Expect attempts to
allocate a pty previously used by someone else, it fails. Upgrade to IRIX 6.1.
Telnet (verified only under SunOS 4.1.2) hangs if TERM is not set. This is a
problem under cron, at and in cgi scripts, which do not define TERM. Thus, you
must set it explicitly - to what type is usually irrelevant. It just has to be
set to something! The following probably suffices for most cases.
set env(TERM) vt100
Tip (verified only under BSDI BSD/OS 3.1 i386) hangs if SHELL and HOME are not
set. This is a problem under cron, at and in cgi scripts, which do not define
these environment variables. Thus, you must set them explicitly - to what type
is usually irrelevant. It just has to be set to something! The following
probably suffices for most cases.
set env(SHELL) /bin/sh
set env(HOME) /usr/local/bin
Some implementations of ptys are designed so that the kernel throws away any
unread output after 10 to 15 seconds (actual number is
implementation-dependent) after the process has closed the file descriptor.
Thus
Expect programs such as
spawn date
sleep 20
expect
will fail. To avoid this, invoke non-interactive programs with
exec
rather than
spawn. While such situations are conceivable, in practice I
have never encountered a situation in which the final output of a truly
interactive program would be lost due to this behavior.
On the other hand, Cray UNICOS ptys throw away any unread output immediately
after the process has closed the file descriptor. I have reported this to Cray
and they are working on a fix.
Sometimes a delay is required between a prompt and a response, such as when a
tty interface is changing UART settings or matching baud rates by looking for
start/stop bits. Usually, all this is require is to sleep for a second or two.
A more robust technique is to retry until the hardware is ready to receive
input. The following example uses both strategies:
send "speed 9600\r";
sleep 1
expect {
timeout {send "\r"; exp_continue}
$prompt
}
trap -code will not work with any command that sits in Tcl's event loop, such as
sleep. The problem is that in the event loop, Tcl discards the return codes
from async event handlers. A workaround is to set a flag in the trap code.
Then check the flag immediately after the command (i.e., sleep).
The expect_background command ignores -timeout arguments and has no concept of
timeouts in general.
There are a couple of things about
Expect that may be non-intuitive. This
section attempts to address some of these things with a couple of suggestions.
A common expect problem is how to recognize shell prompts. Since these are
customized differently by differently people and different shells, portably
automating rlogin can be difficult without knowing the prompt. A reasonable
convention is to have users store a regular expression describing their prompt
(in particular, the end of it) in the environment variable EXPECT_PROMPT. Code
like the following can be used. If EXPECT_PROMPT doesn't exist, the code still
has a good chance of functioning correctly.
set prompt "(%|#|\\$) $" ;# default prompt
catch {set prompt $env(EXPECT_PROMPT)}
expect -re $prompt
I encourage you to write
expect patterns that include the end of whatever
you expect to see. This avoids the possibility of answering a question before
seeing the entire thing. In addition, while you may well be able to answer
questions before seeing them entirely, if you answer early, your answer may
appear echoed back in the middle of the question. In other words, the
resulting dialogue will be correct but look scrambled.
Most prompts include a space character at the end. For example, the prompt from
ftp is 'f', 't', 'p', '>' and <blank>. To match this prompt, you must
account for each of these characters. It is a common mistake not to include
the blank. Put the blank in explicitly.
If you use a pattern of the form X*, the * will match all the output received
from the end of X to the last thing received. This sounds intuitive but can be
somewhat confusing because the phrase "last thing received" can vary
depending upon the speed of the computer and the processing of I/O both by the
kernel and the device driver.
In particular, humans tend to see program output arriving in huge chunks
(atomically) when in reality most programs produce output one line at a time.
Assuming this is the case, the * in the pattern of the previous paragraph may
only match the end of the current line even though there seems to be more,
because at the time of the match that was all the output that had been
received.
expect has no way of knowing that further output is coming unless your
pattern specifically accounts for it.
Even depending on line-oriented buffering is unwise. Not only do programs rarely
make promises about the type of buffering they do, but system indigestion can
break output lines up so that lines break at seemingly random places. Thus, if
you can express the last few characters of a prompt when writing patterns, it
is wise to do so.
If you are waiting for a pattern in the last output of a program and the program
emits something else instead, you will not be able to detect that with the
timeout keyword. The reason is that
expect will not timeout -
instead it will get an
eof indication. Use that instead. Even better,
use both. That way if that line is ever moved around, you won't have to edit
the line itself.
Newlines are usually converted to carriage return, linefeed sequences when
output by the terminal driver. Thus, if you want a pattern that explicitly
matches the two lines, from, say, printf("foo\nbar"), you should use
the pattern "foo\r\nbar".
A similar translation occurs when reading from the user, via
expect_user.
In this case, when you press return, it will be translated to a newline. If
Expect then passes that to a program which sets its terminal to raw
mode (like telnet), there is going to be a problem, as the program expects a
true return. (Some programs are actually forgiving in that they will
automatically translate newlines to returns, but most don't.) Unfortunately,
there is no way to find out that a program put its terminal into raw mode.
Rather than manually replacing newlines with returns, the solution is to use the
command "stty raw", which will stop the translation. Note, however,
that this means that you will no longer get the cooked line-editing features.
interact implicitly sets your terminal to raw mode so this problem will
not arise then.
It is often useful to store passwords (or other private information) in
Expect scripts. This is not recommended since anything that is stored
on a computer is susceptible to being accessed by anyone. Thus, interactively
prompting for passwords from a script is a smarter idea than embedding them
literally. Nonetheless, sometimes such embedding is the only possibility.
Unfortunately, the UNIX file system has no direct way of creating scripts which
are executable but unreadable. Systems which support setgid shell scripts may
indirectly simulate this as follows:
Create the
Expect script (that contains the secret data) as usual. Make
its permissions be 750 (-rwxr-x---) and owned by a trusted group, i.e., a
group which is allowed to read it. If necessary, create a new group for this
purpose. Next, create a /bin/sh script with permissions 2751 (-rwxr-s--x)
owned by the same group as before.
The result is a script which may be executed (and read) by anyone. When invoked,
it runs the
Expect script.
Tcl(3),
libexpect(3)
"Exploring Expect: A Tcl-Based Toolkit for Automating Interactive
Programs" by Don Libes, pp. 602, ISBN 1-56592-090-2, O'Reilly and
Associates, 1995.
"expect: Curing Those Uncontrollable Fits of Interactivity" by Don
Libes, Proceedings of the Summer 1990 USENIX Conference, Anaheim,
California, June 11-15, 1990.
"Using expect to Automate System Administration Tasks"
by Don Libes, Proceedings of the 1990 USENIX Large Installation Systems
Administration Conference, Colorado Springs, Colorado, October 17-19, 1990.
"Tcl: An Embeddable Command Language" by John Ousterhout,
Proceedings of the Winter 1990 USENIX Conference, Washington, D.C., January
22-26, 1990.
"expect: Scripts for Controlling Interactive Programs" by Don
Libes, Computing Systems, Vol. 4, No. 2, University of California Press
Journals, November 1991.
"Regression Testing and Conformance Testing Interactive Programs",
by Don Libes, Proceedings of the Summer 1992 USENIX Conference, pp.
135-144, San Antonio, TX, June 12-15, 1992.
"Kibitz - Connecting Multiple Interactive Programs Together", by
Don Libes, Software - Practice & Experience, John Wiley & Sons,
West Sussex, England, Vol. 23, No. 5, May, 1993.
"A Debugger for Tcl Applications", by Don Libes, Proceedings of
the 1993 Tcl/Tk Workshop, Berkeley, CA, June 10-11, 1993.
Don Libes, National Institute of Standards and Technology
Thanks to John Ousterhout for Tcl, and Scott Paisley for inspiration. Thanks to
Rob Savoye for Expect's autoconfiguration code.
The HISTORY file documents much of the evolution of
expect. It makes
interesting reading and might give you further insight to this software.
Thanks to the people mentioned in it who sent me bug fixes and gave other
assistance.
Design and implementation of
Expect was paid for in part by the U.S.
government and is therefore in the public domain. However the author and NIST
would like credit if this program and documentation or portions of them are
used.