expectperl-discuss

[Expectperl-discuss] blocking expect calls?

[<ex...@th...>]

I'm trying to write a script in perl, using the expect.pm module, which will
connect via ssh to a remote system and run a series of commands.  I can connect
and run commands, but am having trouble with the interactive aspects of the script.

I need to check the status of the system and make calls accordingly, but cannot
find a way to make "blocking" calls (expect, wait, send) or catch the return
value (e.g. send ("ls\n") and catch the results).

Could you folks provide me with sample code or links to documentation that could
help with this?  I've read through the man, er perldoc, page and could not find
solutions there.

thanks,
Andrew
ex...@th...

Re: [Expectperl-discuss] blocking expect calls?

[Bala A. <ba...@sb...>]

Expect doesn't have a blocking mode or concept. Except
gets chunks from the kernel buffer and it isn't always
keeping up with the interacting program. That is,
expect is usually behind and the application it is
interacting with is usually ahead. To sync up both,
(to block like you alluded to) , you need to loop on
the pattern you are looking for. You need to consume
all the patterns that are available on the stdout,
produced either by you "sending" them or produced by
the application. If you pass up any input, then your
expect program may appear to work, but not
consistently. 


Take ls \n for example. You need to loop looking for
the command to return to unix prompt such $ or # or >
or what have you.

While waiting - you should consume everything that
comes your way by using expect(3,'-re', "(.*?)\n") 
(note .*? won't consume \n thus you have hard code \n.

Every time you consume you should put that out to a
buffer such as  $buffer .= $obj->match() ;
Sometimes you may have to use expect_before() but you
have to play with it to see what suits your response
best.

I will be happy to post some samples if you need more
help. Good luck expecting.


B Ayres

--- ex...@th... wrote:
> I'm trying to write a script in perl, using the
> expect.pm module, which will
> connect via ssh to a remote system and run a series
> of commands.  I can connect
> and run commands, but am having trouble with the
> interactive aspects of the script.
> 
> I need to check the status of the system and make
> calls accordingly, but cannot
> find a way to make "blocking" calls (expect, wait,
> send) or catch the return
> value (e.g. send ("ls\n") and catch the results).
> 
> Could you folks provide me with sample code or links
> to documentation that could
> help with this?  I've read through the man, er
> perldoc, page and could not find
> solutions there.
> 
> thanks,
> Andrew
> ex...@th...
> 
> 
>
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Re: [Expectperl-discuss] blocking expect calls?

[Austin S. <te...@of...>]

On Mon, Jul 12, 2004 at 07:23:41PM -0700, Bala Ayres wrote:
> Expect doesn't have a blocking mode or concept.

	Not quite true, case in point: $session->expect();

	If you pass undef as the first argument to expect() it will
block until it has matching patterns. In the example above it will block
until EOF. This is useful e.g. where you wait for a process about to
end but want to make sure it finishes spitting out its output first.

> Except
> gets chunks from the kernel buffer and it isn't always
> keeping up with the interacting program. That is,
> expect is usually behind and the application it is
> interacting with is usually ahead. To sync up both,
> (to block like you alluded to) , you need to loop on
> the pattern you are looking for. You need to consume
> all the patterns that are available on the stdout,
> produced either by you "sending" them or produced by
> the application. If you pass up any input, then your
> expect program may appear to work, but not
> consistently. 
> 
> 
> Take ls \n for example. You need to loop looking for
> the command to return to unix prompt such $ or # or >
> or what have you.
> 
> While waiting - you should consume everything that
> comes your way by using expect(3,'-re', "(.*?)\n") 
> (note .*? won't consume \n thus you have hard code \n.
> 

	You can do a nonblocking grab of existing output by
doing expect(0, '.*'). The advantage being that if there is no
data available it won't wait the 3 seconds as in the example above.

> Every time you consume you should put that out to a
> buffer such as  $buffer .= $obj->match() ;
> Sometimes you may have to use expect_before() but you
> have to play with it to see what suits your response
> best.
> 
> I will be happy to post some samples if you need more
> help. Good luck expecting.
> 

	There are also a few examples included with the tutorial. They
are generally out of date, but maybe a good place to start as well.

	If you have code that would be of general use please copy it here,
perhaps it would be useful to add to the module.

	Austin