Thread: Re: [Expectperl-discuss] Nested telnet sessions using Expect.pm module

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>>> Note:  A know B but doesn't know C - in another words, to get to C you
have
>>> to go through B.

Yes.. well, I guess it depends on what you're trying to say behind the
words.   Remember that you're spawning ONE process (or should be).  Once
you've done that and successfully logged into A, you should INVOKE telnet
client on A to get to B, so there's no more "spawning" (from a perl module
perspective), as B and C have no clue what the heck SPAWN is.. they just
know what telnet is.  Just imagine that you are invoking telnet on the
command line from host to host to host, and that's ultimately what expects
doing with the single telnet session you spawned to A.  Imagine it that way
and you should be able to see enough of what's going on to know how to use
expect and code it.  Remember that each time you hop, the STDOUT and STDERR
channels get lashed together, and become STDIN to the thing that created it
(parent.)  They all get lashed together like the Alaskan pipeline, all the
way back to your original spawned process in your expect script.  In this
daisy-chain telnet example you're trying to do, it is the only STDIN that
your script should be dealing with.

I don't know if that's the understanding you need, or if I'm confusing you
more.  Bottom line, If you can do it from the command line, i.e., telnet
from A to B to C and so forth, then so can expect.  If you can't do it,
then neither can expect.  It's that simple.  All expect does is provide a
way to automate the steps.  The only difference between opening a process
in Perl vs. Expect is that perl (by itself) cannot open a bi-directional
pipe to a process.  I.e., it can do this

     open (TELNET, " telnet $HOSTA | ");

which would allow you to read from the session, or you can do this:

     open (TELNET, "| telnet $HOSTA ");

to write to the process, but you cannot do both at the same time like this:

     open (TELNET, "| telnet $HOSTB | ");

that's where Expect can help.  The telnet module is an alternative that
also does this, but only for telnet.  Can't spawn a chess program on the
command line and interact with it using telnet module, but you can do it
using Expect (for all you telnet.pm zealots out there, that's the
difference)

If you want to look at primitive code that represents this idea, then it
would look something like this:

use Expect;

$HOSTA=xx.xx.xx.1;
$HOSTB=xx.xx.xx.2;
$HOSTC=xx.xx.xx.3;

$username="abc";
$password="123";

#------------
# telnet to A
#------------
my $exp = Expect->spawn("telnet $HOSTA") or die "Cannot spawn telnet: $!
\n";
$timeout=20;
expect($timeout, "login: ");
$exp->send("$username\n");
expect($timeout, "password: ");
$exp->send("$password\n");
$expect($timeout, '-re', "[%#>] $");         # $HOSTA prompt

#------------
# telnet to B
#------------
$exp->send("telnet $HOSTB\n");
expect($timeout, "login: ");
$exp->send("$username\n");
expect($timeout, "password: ");
$exp->send("$password\n");
$expect($timeout, '-re', "[%#>] $");         # $HOSTB prompt

#------------
# telnet to C
#------------
$exp->send("telnet $HOSTC\n");
expect($timeout, "login: ");
$exp->send("$username\n");
expect($timeout, "password: ");
$exp->send("$password\n");
$expect($timeout, '-re', "[%#>] $");         # $HOSTC prompt

Braindead simple example, but you should get the idea.  Do a perldoc on
Expect.pm and print it out, go to staples and buy a binder, put it in there
and carry it around / put it on your desk at work also.  If you REALLY want
to get nuts and rule the world with Expect, go out and buy Don Libes most
excellent O'Reilly book.  Tcl is such a simple language, that you would
have no problem figuring enough of it out on the fly to literally use this
book as a supercharged reference for the Perl module, that is, unless
you're a Perl zealot and can't for religious reasons..  although the perl
module is not 100% translation, it's close enough for government work (so
the saying goes.)

Anyways, hope this helps you man.

                    Hailey Nguyen                                                                                       
                    <Hai...@Su...>                     To:     Chris Muth <mut...@mc...>                
                    Sent by:                                    cc:     Hailey Nguyen <Hai...@Su...>,          
                    exp...@li...urc        exp...@li...                
                    eforge.net                                  Subject:     Re: [Expectperl-discuss] Nested telnet     
                                                                sessions using   Expect.pm module                       

                    10/02/2003 04:11 PM                                                                                 

Hi Chris,

>>> First you will have to login to A.  That involves what you have, plus
>>> you will have to $exp->expect() for whatever telnet responds with when
>>> it asks for the password.  Then use a $exp->send() to send the
password.
>>> Then $exp->expect() for the prompt on A.  Once you are logged into A,
>>> use a $exp->send() to call telnet $B on A to login to B, $exp->expect()
>>> for the password prompt, and then $exp->send() it.  Once logged into B,
>>> do the same to login to C, and the same for D, and the same for ...

Still struggling with this. As soon as I logged into B from A I lose
control of that session/connection. So $exp->send() won't do anything.
Did you write something like this before. Can I have an example?

Note:  A know B but doesn't know C - in another words, to get to C you have
to go through B.

Thanks a million,
Hailey

>>>>
>>>> Please show me how to do nested telnet sessions using Expect.pm
module?
>>>>
>>>> 1- telnet to machine A
>>>> 2- from A to mcahine B
>>>> 3- from B to machine C
>>>>
>>>> -----
>>>> use Expect;
>>>>
>>>> my $exp = Expect->spawn("telnet $somehost")
>>>>    or die "Cannot spawn telnet: $!\n";
>>>>
>>>> ...
>>>>
>>>> -----
>>>> Your help is greatly appreciated. Please reply directly to me since
>>>> I am not on the alias.
>>>>

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