autoexpect(1)
AUTOEXPECT(1) USER COMMANDS AUTOEXPECT(1)
NAME
autoexpect - generate an Expect script from watching a ses-
sion
SYNOPSIS
autoexpect [ args ] [ program args... ]
INTRODUCTION
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 autoexpect.
The simplest way to use autoexpect is to call it from the
command line with no arguments. For example:
% autoexpect
By default, autoexpect spawns a shell for you. Given a pro-
gram 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 speci-
fied), 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:
o 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
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AUTOEXPECT(1) USER COMMANDS AUTOEXPECT(1)
up at one spot, try adding a short sleep just
before the previous send.
You can force this behavior throughout by overrid-
ing the variable "force_conservative" near the
beginning of the generated script. This "conserva-
tive" mode makes autoexpect automatically pause
briefly (one tenth of a second) before sending each
character. This pacifies every program I know of.
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
this behavior.
The following example starts autoexpect in conser-
vative mode.
autoexpect -c
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 conser-
vative mode with ^L as the toggle.
autoexpect -c -C ^L
o Echoing. Many program echo characters. For exam-
ple, if you type "more" to a shell, what autoexpect
actually sees is:
you typed 'm',
computer typed 'm',
you typed 'o',
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AUTOEXPECT(1) USER COMMANDS AUTOEXPECT(1)
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. How-
ever, it could conceivably be incorrect if you
really had to wait to see each character echoed.
o 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.
autoexpect -p
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.
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AUTOEXPECT(1) USER COMMANDS AUTOEXPECT(1)
autoexpect -p -P ^P
OTHER FLAGS
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
STYLE
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 useful.
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.
SEE ALSO
"Exploring Expect: A Tcl-Based Toolkit for Automating
Interactive Programs" by Don Libes, O'Reilly and Associates,
January 1995.
AUTHOR
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.
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