autoexpect - generate an Expect script from watching a session
autoexpect [ args ] [ program args... ]
autoexpect watches you interacting with another program and creates an
Expect script that reproduces your interactions. For straightline
scripts, autoexpect saves substantial time over writing scripts by
hand. Even if you are an Expect expert, you will find it convenient to
use autoexpect to automate the more mindless parts of interactions. It
is much easier to cut/paste hunks of autoexpect scripts together than
to write them from scratch. And if you are a beginner, you may be able
to get away with learning nothing more about Expect than how to call
The simplest way to use autoexpect is to call it from the command line
with no arguments. For example:
By default, autoexpect spawns a shell for you. Given a program name
and arguments, autoexpect spawns that program. For example:
% autoexpect ftp ftp.cme.nist.gov
Once your spawned program is running, interact normally. When you have
exited the shell (or program that you specified), autoexpect will
create a new script for you. By default, autoexpect writes the new
script to "script.exp". You can override this with the -f flag
followed by a new script name.
The following example runs "ftp ftp.cme.nist.gov" and stores the
resulting Expect script in the file "nist".
% autoexpect -f nist ftp ftp.cme.nist.gov
It is important to understand that autoexpect does not guarantee a
working script because it necessarily has to guess about certain things
- and occasionally it guesses wrong. However, it is usually very easy
to identify and fix these problems. The typical problems are:
· Timing. A surprisingly large number of programs (rn, ksh,
zsh, telnet, etc.) and devices (e.g., modems) ignore
keystrokes that arrive "too quickly" after prompts. If you
find your new script hanging up at one spot, try adding a
short sleep just before the previous send.
You can force this behavior throughout by overriding the
variable "force_conservative" near the beginning of the
generated script. This "conservative" mode makes autoexpect
automatically pause briefly (one tenth of a second) before
sending each character. This pacifies every program I know
This conservative mode is useful if you just want to quickly
reassure yourself that the problem is a timing one (or if
you really don’t care about how fast the script runs). This
same mode can be forced before script generation by using
the -c flag.
Fortunately, these timing spots are rare. For example,
telnet ignores characters only after entering its escape
sequence. Modems only ignore characters immediately after
connecting to them for the first time. A few programs
exhibit this behavior all the time but typically have a
switch to disable it. For example, rn’s -T flag disables
The following example starts autoexpect in conservative
The -C flag defines a key to toggle conservative mode. The
following example starts autoexpect (in non-conservative
mode) with ^L as the toggle. (Note that the ^L is entered
literally - i.e., enter a real control-L).
autoexpect -C ^L
The following example starts autoexpect in conservative mode
with ^L as the toggle.
autoexpect -c -C ^L
· Echoing. Many program echo characters. For example, if you
type "more" to a shell, what autoexpect actually sees is:
you typed ’m’,
computer typed ’m’,
you typed ’o’,
computer typed ’o’,
you typed ’r’,
computer typed ’r’,
Without specific knowledge of the program, it is impossible
to know if you are waiting to see each character echoed
before typing the next. If autoexpect sees characters being
echoed, it assumes that it can send them all as a group
rather than interleaving them the way they originally
appeared. This makes the script more pleasant to read.
However, it could conceivably be incorrect if you really had
to wait to see each character echoed.
· Change. Autoexpect records every character from the
interaction in the script. This is desirable because it
gives you the ability to make judgements about what is
important and what can be replaced with a pattern match.
On the other hand, if you use commands whose output differs
from run to run, the generated scripts are not going to be
correct. For example, the "date" command always produces
different output. So using the date command while running
autoexpect is a sure way to produce a script that will
require editing in order for it to work.
The -p flag puts autoexpect into "prompt mode". In this
mode, autoexpect will only look for the the last line of
program output - which is usually the prompt. This handles
the date problem (see above) and most others.
The following example starts autoexpect in prompt mode.
The -P flag defines a key to toggle prompt mode. The
following example starts autoexpect (in non-prompt mode)
with ^P as the toggle. Note that the ^P is entered
literally - i.e., enter a real control-P.
autoexpect -P ^P
The following example starts autoexpect in prompt mode with
^P as the toggle.
autoexpect -p -P ^P
The -quiet flag disables informational messages produced by autoexpect.
The -Q flag names a quote character which can be used to enter
characters that autoexpect would otherwise consume because they are
used as toggles.
The following example shows a number of flags with quote used to
provide a way of entering the toggles literally.
autoexpect -P ^P -C ^L -Q ^Q
I don’t know if there is a "style" for Expect programs but autoexpect
should definitely not be held up as any model of style. For example,
autoexpect uses features of Expect that are intended specifically for
computer-generated scripting. So don’t try to faithfully write scripts
that appear as if they were generated by autoexpect. This is not
On the other hand, autoexpect scripts do show some worthwhile things.
For example, you can see how any string must be quoted in order to use
it in a Tcl script simply by running the strings through autoexpect.
"Exploring Expect: A Tcl-Based Toolkit for Automating Interactive
Programs" by Don Libes, O’Reilly and Associates, January 1995.
Don Libes, National Institute of Standards and Technology
expect and autoexpect are in the public domain. NIST and I would
appreciate credit if these programs or parts of them are used.
30 June 1995 AUTOEXPECT(1)