InfoMagic Source Code 1993 July/THE_SOURCE_CODE_CD_ROM.iso/languages/tcl/expect/expect-4.7/FAQ

Text File | 1993-04-12 | 26.9 KB | 651 lines

This is the Frequent-Asked-Questions (FAQ) file for Expect

This file represents questions I've received (with answers I've given)
about subjects that don't fit in the man page for one reason or
another.  In some cases, I've left the original questions.  I suppose
I could've stripped off the headers, but it seems more realistic to
see actual people who've asked the questions.  Thanks to everyone who
asked.

Hopefully, no one is embarrassed by seeing their name here.  If
anything, this probably reflects most poorly on me because it shows a
number of ideas other people would like me to add to Expect, that I
haven't.

Long rows of hyphens separate the different topics.  In cases where
I've reprinted the original question-letter and my answer, the two are
separated by a short row of hyphens.

The papers listed in the README file should also be consulted for highly
technical or philosophical discussion of the implementation, design and
practical application of Expect.

-Don

Here is a short summary of each question/answer.  You can search for
the number, for example, "#4" once you've found the subject you're
looking for.

#1 Why does expect need to be setuid root on Cray?
#2 Why isn't there an expect mailing list?
#3 How do you pronounce "Ousterhout" anyway?  (Or "Libes" for that matter?)
#4 How about distributing a test suite - or - just what are those other
    programs further down in the Makefile?
#5 Can expect automatically generate a script from watching a session?
#6 What do you think about the Perl rewrite of Expect?
#7 Why should I learn yet another language (Tcl) instead of writing my
    interaction in <a language I already know>.
#8 How come I get "ioctl(set): Inappropriate ..., bye recursed" ...
#9 Do we need to pay or ask for permission to distribute Expect?
#10 Can Expect understand screen-oriented (curses) programs?
#11 Why doesn't Expect kill telnet (or other programs) sometimes?
--------------------------------------------------------------------------
#1
From: libes (Don Libes)
To: [e-mail] (Lori Wong)
Subject: setuid in expect
Date: Thu, 24 Oct 91 16:15:20 EDT

>     I have been running expect now under UNICOS 6.1 and CSOS 1.0 (Cray
>Computer Corporation's OS).  The two machines that I am running expect
>on have stringent security features, one of which is to limit setuid
>privileges to specific individuals.  I was wondering if you would be
>kind enough to explain the purpose of the setuid that is needed by expect
>and whether it could be compiled to run without having to have setuid
>privilege?  I know it has to do with spawning and communicating with
>the various spawned tasks, but don't know enough of the details to be
>able to explain why expect specifically needs setuid and whether or not
>it could cause a security problem (could someone use it to enter into
>the system and wreak havoc, for example?).  Right now, I've limited
>the access of expect to my group, but need to know what the security
>implications are if I open it to all users.  I'd appreciate any light
>you can shed on this subject...

Root-access is needed to open a pty under Unicos.  Thus, all programs
accessing ptys must be setuid root.  If you do an "ls -l" of programs
like "script", "xterm", etc, you'll see this.

I have no idea why this is.  The requirement was probably for security
reasons to begin with, but it has the ironic effect of making more
programs require setuid and therefore greater possibility of errant
setuid programs.

In fact, there is one known Unicos bug relating to the way uids are
switched at exec time which requires further special coding.  If you
search for "Cray" in the Expect source you will see significant chunks
of code to get around the problem.

I don't know if this reassures you any.  All I can tell you is that a
number of Cray experts have looked into the situation and are happy
with the current implementation of Expect.

Don
--------------------------------------------------------------------------
#2
From: libes (Don Libes)
To: [e-mail] (David R. Clark)
Subject: Mailing list for expect
Date: Mon, 23 Sep 91 18:21:28 EDT

>Would be nice if their were an expect mailing list.  I would use it more
>often, and be made aware of other users.

Perhaps I'm too myopic, but I don't see the need for it.  I typically
get two or three expect questions a week, which I answer myself.

For one reason or another (usually a bug fix, but often, just revising
the documentation), I update expect about once every two weeks.
Personally, I'd hate being on the other end of something like this.
Who needs patches every two weeks for problems that probably aren't
even relevant to you?

>It would be helpful, too, if this served as an area for swapping programs.
>Many of the things that I want to do are done by others already.

Send me things that you'd like to distribute.  I'll either include
them with expect or put it in a publicly accessible directory so other
people can get it.  Yes, I know it's not as good as getting notified
via a mailing list, but actually I doubt there's such a need.  The
reality is that most of the programs expect is applied to have
poorly defined interfaces.  There are few portable expect scripts.

For example, you can't even write a guaranteed-portable script that
knows what a shell prompt looks like because everyone customizes them!
And the ftp scripts don't work on everyone's ftp because the ftp user
interface is not specified by the standard, so everyone's is
different.  And so on.

There is a Tcl newsgroup, comp.lang.tcl, which many expect users read.
It's pretty good for asking questions about Tcl, and there isn't that
much traffic that an occasional Expect question isn't looked upon
favorably.  Indeed, some of the sharpest Tcl hackers read the mailing
list, so I post news about new-releases of expect there first.  The
newsgroup is gatewayed to a mailing list ([e-mail])
which is further described in the Tcl documentation.

Don
--------------------------------------------------------------------------
#3
From: [e-mail] (John Ousterhout)
To: [e-mail]
Subject: Re: pronunciation?
Date: Tue, 29 May 90 21:26:10 PDT

Those of us in the family pronounce it "OH-stir-howt", where the
first syllable rhymes with "low", the second with "purr", and the
third with "doubt".  Unfortunately this isn't the correct Dutch
pronounciation for a name spelled this way (someplace along
the line it got misspelled:  it was originally "Oosterhout"), nor
is it what you'd guess if you use common sense.  So, we've gotten
used to responding to almost anything.

                    -John-

I suppose I should say something in kind.  "Libes" is pronounced
"Lee-bus" with stress on the first syllable.  Like John, though, I've
gotten used to responding to anything close. - Don
--------------------------------------------------------------------------
#4
From: libes (Don Libes)
To: [e-mail]
Subject: testing expect
Date: Mon, 17 Sep 90 14:33:51 EDT

>This is the header of the shar I have of expect.  The
>following files referred to in the Makefile were not
>included:
>    test/Makefile
>    test/checkall
>    ptytest
>    dumb.c
>    exho.c
>
>Is there a newer shar that has the test programs?

No.  These files are part of a test suite that I use.  However, I'm
not distributing them (yet) because they are too fragile.  (One of our
less experienced students wrote them, and he didn't do a very good
job, I'm afraid.  I have to go back and clean them up at some point.)
But it's not high on my priority list.

In the meantime, try some of the programs distributed in the test
directory.  They are a strong indication of whether expect works or
not.  If you any problems with them, let me know.

Don
--------------------------------------------------------------------------
#5
From: libes (Don Libes)
To: [e-mail]
Subject: expect
Date: Fri, 12 Oct 90 17:16:47 EDT

>I like "expect" and am thinking of using it to help automate the
>testing of interactive programs.  It would be useful if expect had a
>"watch me" mode, where it "looks over the shoulder" of the user and
>records his keystrokes for later use in an expect script.
>
>(Red Ryder and other Macintosh telecommunications packages offer this
>sort of thing.  You log onto Compuserve once in "watch me" mode, and
>RR keeps track of the keystrokes/prompts.  When you're done you have a
>script that can be used to log onto Compuserve automatically.)

I'd like to see how they do it.  The major problem is when you type
characters, they are invariably echoed.  So if you "interact" with a
system and type "finger", what expect sees is that
you typed 'f',
computer typed 'f',
you typed 'i',
computer typed 'i',
you typed 'n',
computer typed 'n',
...

I.e. expect has no way of knowing that you weren't waiting to see the
computer say 'f', before you typed 'f'.

You'd have to handle problems like this, kind of guessing if the
computer is echoing or you are really waiting for the response.  The
system actually doesn't echo exactly what you type, making this even
harder.  And there are other problems: sometimes characters get lumped
together rather than sent separately, sometimes echoing is turned off
for you.

If you run expect in debug mode while doing "interact", you'll see
what I mean.

Given that you'd have to do such severe editing of an automatically
produced script, I figure writing the script from scratch is easier.

Actually, I suggest you used the interact facility (or the UNIX script
program) and just edit the output.  Invariably, you want to change a
lot of text to *s and add alternatives (i.e. a lot of editing) anyway.

Do you have to do much editing with scripts that Red Ryder produces?
How does it handle these problems?  Does it support regular
expressions and alternation?  (Obviously, a computer-generated script
can't generate these automatically.)  Do you have to tell it whether
you are full/half-duplex or what kind of line-termination characters
you are using?

Is there anything else in Red Ryder that would be useful in expect?

>Before I look into adding a "watch me" feature, I thought I should
>ask: has this been done already?

You're welcome to give it a shot.  I'd be interested to see what you
come up with.

Don

------------------

From: (Pete TerMaat) <[e-mail]>
To: [e-mail] (Don Libes)
Subject: Re: expect
Date: Thu, 17 Jan 91 12:30:01 -0600

 > >I like "expect" and am thinking of using it to help automate the
 > >testing of interactive programs.  It would be useful if expect had a
 > >"watch me" mode, where it "looks over the shoulder" of the user and
 > >records his keystrokes for later use in an expect script.
 > >
 > >(Red Ryder and other Macintosh telecommunications packages offer this
 > >sort of thing.  You log onto Compuserve once in "watch me" mode, and
 > >RR keeps track of the keystrokes/prompts.  When you're done you have a
 > >script that can be used to log onto Compuserve automatically.)
 >
 > I'd like to see how they do it.  The major problem is when you type
 > characters, they are invariably echoed.

 > You'd have to handle problems like this, kind of guessing if the
 > computer is echoing or you are really waiting for the response.

That appears to be what Red Ryder does.  It works surprisingly well
for line-oriented things.  It produces unnecessarily lengthy (though
still working) scripts when you make a lot of corrections by
backspacing.  And it isn't suitable for character-oriented things like
editors, where there is no notion of a prompt.

 > If you run expect in debug mode while doing "interact", you'll see
 > what I mean.

Ah, thanks for the tip.  I hadn't appreciated the problem.

 > Actually, I suggest you used the interact facility (or the UNIX script
 > program) and just edit the output.  Invariably, you want to change a
 > lot of text to *s and add alternatives (i.e. a lot of editing) anyway.

I'm working with text editors and document viewers, so for every
character typed there can be a lot of output.  It wouldn't make sense
for me to wade through all that output and trim it down.

Writing the scripts from scratch, as you suggested, is currently my
best approach.  I'm also experimenting with a command which logs just
the input.

 > Do you have to do much editing with scripts that Red Ryder produces?

Here's an example from Microphone (another Macintosh communications
program), which is not as sophisticated in its watchme mode as Red
Ryder.  I had it watch me while I typed "echo this is a test" to the
shell.  It's pretty stupid, but (to my surprise) the script
nevertheless works, without any editing.

    6   Wait for Text  "% "
    7   Send Text String  "echo"
    8   Wait for Text  "% ech"
    9   Send Text String  " "
    10  Wait for Text  "echo "
    11  Send Text String  "this"
    12  Wait for Text  "o thi"
    13  Send Text String  " "
    14  Wait for Text  "this "
    15  Send Text String  "is a "
    16  Wait for Text  "is a "
    17  Send Text String  "te"
    18  Wait for Text  " a te"
    19  Send Text String  "st"
    20  Wait for Text  " test"
    21  Send Text String  "^M"
    22  Wait for Line Containing  " test"

Here's an example of the same thing done with Red Ryder watching.
Much better!

    PROMPT %
    PAUSE
    TYPE echo this is a test^M
    PROMPT %

Red Ryder appears to keep track of what was typed and eliminate that
from any possible prompts.  As you pointed out, what was typed is not
always what was printed, but in my experience (mostly using it to dial
up to UNIX sites) this hasn't been a problem.

 > How does it handle these problems?  Does it support regular
 > expressions and alternation?  (Obviously, a computer-generated script
 > can't generate these automatically.)

No, just literals.  Red Ryder won't go back further than the last line
of output, which usually works better than Microphone's more generous
approach.

 > Do you have to tell it whether you are full/half-duplex or what
 > kind of line-termination characters you are using?

Since it's a communications program it already has the info, but I
don't know that it uses this information when it creates the scripts.

 > Is there anything else in Red Ryder that would be useful in expect?

Good question.  I think expect has these programs beat though, with
the exception of a watchme feature.  A visual interface would be nice,
as one thing that I miss from Red Ryder is the status line, which
tells you the current command.  (I know you can sort of simulate this
by tracing the TCL code.)  Some of my expect scripts are long and it's
helpful to know what they are sending/expecting when they pause/hang.
As long as I'm dreaming, it would also be nice if I could single-step
through a script by pressing a "single-step" button.  I guess these
are more TCL issues than expect issues.

Microphone has a nice interface for novices.  You can write a script
with very little typing by pointing and clicking from menus of
keywords.  Red Ryder's language is less verbose and probably more
powerful, but neither is as powerful/flexible as expect/TCL.

 > >Before I look into adding a "watch me" feature, I thought I should
 > >ask: has this been done already?
 >
 > You're welcome to give it a shot.  I'd be interested to see what you
 > come up with.

Since it's not quite so useful for character-oriented editors as for
line-oriented things, I've decided for now just to write the scripts
from scratch.

I'll say again that I like the tool a lot--nice work!  There are other
people here using it for things like the testing of ksh, which
responds differently to signals when not used interactively.

I have some mods to make expect run on a Cray.  I was sort of waiting
to see if the mods are Cray-specific or System V specific before
forwarding them, but if you would like to incorporate them right away
I will send them.

-- Pete

--------------------------------------------------------------------------
#6
From: [e-mail] (Don Libes)
Subject: Re: Expect.pl, alpha release
Date: 2 Nov 90 03:06:40 GMT

In article <[e-mail]> [e-mail] (Randal Schwartz) writes:
>The motivation for writing this package is the fact
>that Don Libes doesn't like Perl. :-)

I've never said anything like that, nor is it true (although I will admit
that I've had a lot of trouble learning Perl.)  Fact is, I've written
several Perl hacks, at least one of which is used daily at my site.

>The matchup of expect<->tcl and expect.pl<->Perl made for some weird
>design tradeoffs.  I may start from mostly scratch and do everything
>right.  That is probably why I hesitate to implement the rest of the
>functions... they really don't fit in a Perl environment.

Actually, I discussed these issues with several people during the
development of expect.  The approach I took effectively sealed off the
user from the underlying C implementation, substituting the more shell-
like Tcl language and reducing the ability to screw themselves somehow.

In the approach you took, the user language IS Perl, which provides
incredible power and flexibility.  The primary disadvantage is that
the user may have to learn Perl, which is hard.

Also, as you noticed, some of the features (like logging) are a problem
for Perl.  Oh, and as you suspected, recursive invocations are useful -
consider writing scripts that are half automated and half interactive,
like the fsck script I showed at the LISA conference.

Please don't get me wrong.  I think Perl is very useful.  I desperately
want a copy of your book.  And I consider it a compliment that you
followed my implementation as faithfully as you did.  Though, I did
think some of your Perl code pretty weird!

Actually, in my USENIX paper I stated that I fully expected someone to
incorporate the expect primitives into a shell, Perl, whatever.  I was
just showing proof of concept.  It just happened to turn out to be
worth keeping around.

In fact, I owe a lot for it to John Ousterhout who wrote Tcl.

Don Libes          [e-mail]      ...!uunet!cme-durer!libes
------------------
Article 10362 in comp.lang.perl:
From: [e-mail] (Randal L. Schwartz)
Subject: Re: perl4.035 & Solaris2.1 & sockets problem
Message-ID: <[e-mail]>
Date: 18 Feb 93 16:01:26 GMT
References: <[e-mail]> <[e-mail]>
Organization: Stonehenge Consulting Services; Portland, Oregon, USA
Lines: 26
In-Reply-To: dnoble@hobbs's message of 17 Feb 93 22:14:30 GMT

>>>>> In article <[e-mail]>, dnoble@hobbs (David Noble) writes:
David> Check to see if 'sys/socket.ph' is required by the script. If it's not
David> there, the script may have hard-coded some constants that are different
David> under Solaris. Reminds me of some code in chat2.pl:
David>         unless (socket(S, 2, 1, 6)) {
David>                 # XXX hardwired $AF_SOCKET, $SOCK_STREAM, 'tcp'
David>                 # but who the heck would change these anyway? (:-)

Yup.  I've been bitten by this code (*my* code) myself when I moved to
a blecchy sysV environment.

All because I had used chat2 on only the few boxes (all BSD-derived)
that I had access to at the time, and I was too lazy to run h2ph. :-)

*Someday* soon, after the 5.0 camel update, and Learning Perl hits the
stands, I'm going to rewrite the chat2 stuff to make it portable, add
some documentation, and then release it (finally!) as a Beta release.
(It's still just an alpha, folks!  Enough stuff to make it work for
*my* needs, but not really meant as a general tool yet!... sigh.)

print "Just another Perl [book and class, but not lib code :-] hacker,"
--
Randal L. Schwartz
--------------------------------------------------------------------------
#7
From: libes (Don Libes)
To: Aamod Sane <[e-mail]>
Cc: libes
Subject: Re: Expect, Tcl, programmed dialogue etc.
Date: Mon, 2 Sep 91 15:47:14 EDT

>    >>A friend told me about "expect". But then, I have to know the
>    >>idiocies of "tcl". I would like to know if there is an alternative
>    >>to expect that is also useful in other places, so that I do not
>    >>have to spend time getting used to tcl for just this one tool.
>
>    Your reasoning is shortsighted.  Tcl is a language that can be used in
>    other applications.  It won't be a waste of your time to learn it.
>
>I have nothing against tcl as such.
>The reluctance to learn it comes mainly from the feeling that half my
>life seems to be spent learning new languages that differ very little
>from existing ones, and differ in annoying little details at that.
>To add to the misery, every implementation has its own
>idiosyncracies...:-(

Ironically, Tcl was written specifically to halt this very problem.

The author recognized that every utility seems to have its own
idiosyncratic .rc file or programming language.  Tcl was designed as a
general-purpose language that could be included with any utility, to
avoid having everyone hack up their own new language.

In this context, your statements to the newsgroup do Tcl a great
disservice.

Don
------------------------------------------------------------------------
#8
From: [e-mail] (James B. Davis)
To: [e-mail]
Subject: How come I get "ioctl(set): Inappropriate ..., bye recursed" ...
Date: Tue, 10 Dec 91 10:47:21 MST

Every time I ^C out of a expect script run I get:

ioctl(set): Inappropriate ioctl for device
bye recursed

Is this standard or am I doing something wrong?

[e-mail]
---------------
From: Michael Grant <[e-mail]>
Subject: Re: How come I get "ioctl(set): Inappropriate ..., bye recursed" ...
Date: Tue, 10 Dec 91 16:05:01 EST

The problem was that I hadn't run the fixincludes shellscript and
recompiled gcc with itself during gcc installation.  I recompiled gcc
with itself, then ran the fixincludes script, the messages went away.

Michael Grant

--------------------------------------------------------------------------
#9
From: libes (Don Libes)
To: Mohammad Reza Jahanbin <[e-mail]>
Subject: Copyright Question.
Date: Tue, 26 Jan 93 23:46:24 EST

Mohammad Reza Jahanbin writes:
>Before anything let me thank you on behalf of ComputeVision R&D for
>putting so much effort into expect. Part of CV has been using expect
>for the past two years or so to build variety of tools including an
>automated testbed for a product.
>
>CV is currently considering shipping the automated testbed to some of its
>retailers, to enable them to perform their own tests before distributing
>the product.
>
>The Question is, are we allowed to ship expect? Do we need to ask
>anyone for permission? Do we need to say or write anything in the
>documentation? Do we need to pay for it?
>
>I have not been able to find any copyright (or indeed copyleft) notices
>in the usual expect distribution. Would you be able to clarify our position.

Sorry to delay in responding.  I sent your request to my management
and they had to discuss it (if they didn't, there would be no reason
to pay them).  While they continue to discuss it, I can tell you
informally the gist of what they will eventually say:

You are allowed to do just about anything with Expect.  You can even
sell it.  You need not ask our permission.  You need not pay for it.
(It is my understanding that your tax dollars, in effect, already have
paid for it.)

You cannot claim that you wrote it (since this would be a lie), nor
can you attempt to copyright it (this would be fruitless as it is a
work of the US government and therefore not subject to copyright).

NIST would appreciate any credit you can give for this work.  One line
may suffice (as far as I'm concerned) although there should be
something to the effect that this software was produced for research
purposes.  No warantee, guarantee, liability is implied.

My management would appreciate it if you sent a letter on your company
letterhead suitably praising Expect and briefly describing how it has
helped your business.  Send this to the following individuals:

John Lyons, Director
NIST
Admin Bldg, Rm A-1134
Gaithersburg, MD 20899

John Simpson, Director, Manufacturing Engineering Laboratory
NIST
Bldg 220, Rm B-322
Gaithersburg, MD 20899

Howard Bloom, Factory Automation Systems Division
NIST
Bldg 220, Rm A-127
Gaithersburg, MD 20899

Jeane Ford, Product Data Engineering Group
NIST
Bldg 220, Rm A-127
Gaithersburg, MD 20899


If you feel more indebted than a letter can express, your company can
sign a CRADA (Cooperative Research and Development Agreement) with
NIST.  This is a contract that can be customized as you like.
Typically, CRADA's state that we give you explicit permission to
distribute or commercialize our code, and that we are willing not to
divulge any company secrets you tell us.  CRADA's can also state
that we will share further developments with you, or that you are
giving us money or software, or even just sending us bugs, fixes and
experiences.

These contracts are looked upon by Congress as an indication that we
are helping American industry (i.e., doing our job).  Even though they
seem vague and almost pointless, they essentially are brownie points
for NIST when it comes to asking for funding from Congress each year.

I hope this has answered your questions.  Let me know if you have
further questions.

Don
----------------------------------------------------------------------
#10 Can Expect understand screen-oriented (curses) programs?

Mark Weissman ([e-mail]) and Christopher Matheus modified a
version of Expect that has a built-in Curses emulator with commands to
expect patterns by rows and columns.  It even understands patterns
such as highlight and underscore.

This program is called Expecterm and can ftp'd from
harbor.ecn.purdue.edu (128.46.128.76) or ftp.ibp.fr (132.227.60.2) as
/tcl/extensions/expecTerm1.0beta.tar.Z

Subject to experience, Expecterm is likely to change rapidly (the user
interface, especially) so we have not integrated this into the
main-line of Expect.  When Expecterm settles down, it will be combined
with Expect itself.

----------------------------------------------------------------------
#11 Why doesn't Expect kill telnet (or other programs) sometimes?

To: [e-mail]
Subject: Re: need help running telnet expect script from cron on sunos 4.1.3
--text follows this line--
[e-mail] writes:
>       The only problem I am still having with the script I wrote is that
>    the telnet does not seem to die on it's own, unless I turn on debugging.

Actually, Expect doesn't explicitly kill processes at all.  Generally,
processes kill themselves after reading EOF on input.  So it just seems
like Expect kills all of its children.

>    I was forced to save the pid of the spawned telnet, and kill it with an
>    'exec kill $pid' in a proc that is hopefully called before the script
>    exits. This seems to work fine, but it makes me nervous since omnet
>    charges for connect time, and leaving a hung telnet lying around could
>    get expensive. I warned the rest of the staff so that they will also be
>    on the lookout for any possible hung telnets to omnet.

The problem is that telnet is not recognizing EOF.  (This is quite
understandable since real users can't actually generate one from the
telnet user interface.)  The solution is to either 1) explicitly drive
telnet to kill itself (i.e., a graceful logout) followed by "expect
eof" or 2) "exec kill" as you are doing.

Don