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EXPECT(1) |
FreeBSD General Commands Manual |
EXPECT(1) |
expect - programmed dialogue with interactive programs, Version 5
expect [ -dDinN ] [ -c cmds ] [ [
-[f|b] ] cmdfile ] [ args ]
Expect is a program that "talks" to other interactive programs
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.
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