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Full Discussion: Signal handling in Perl
Top Forums Shell Programming and Scripting Signal handling in Perl Post 302152331 by drl on Wednesday 19th of December 2007 03:44:31 PM
Old 12-19-2007
Hi.

This worked for me. Here's the simple driver script:
Code:
#!/bin/sh -

# @(#) s1       Demonstrate catching signal in perl, return to shell.

echo
echo " Calling perl script."

./user1

echo
echo " Returned from perl script."

exit 0

and the perl script it calls is:
Code:
#!/usr/bin/perl

$SIG{'INT'} = 'Handler';

#some code
print "\n Will wait for you to enter ^C ";
my ($junk) + <>;

#signal handling

sub Handler {
  print "\n Caught ^C \n";
  exit(0);
}

I moved the hash setting above the print and read. Executed twice, once with a simple RETURN and once with ^C yields:
Code:
user-problem/228 % ./s1

 Calling perl script.

 Will wait for you to enter ^C

 Returned from perl script.
user-problem/228 % ./s1

 Calling perl script.

 Will wait for you to enter ^C
 Caught ^C

 Returned from perl script.

So in both cases, control returns to the shell. My understanding is that signals are caught by the perl process, but not seen by the shell process, like most things for parent-child processes.

If you replaced the shell process with the perl script, say with exec, then the behavior described by the OP would be seen. I verified that with a separate script.

The Programming Perl 3rd, p 413, advises not doing much in the handler beyond setting a global variable, q.v. So I suppose it's possible that if you had a lot of code in the handler, you might run into trouble; PP suggests that a memory fault could occur, even for print statements.

Do this help or confuse the issue? ... cheers, drl
Last edited by drl; 12-19-2007 at 04:52 PM.. Reason: Add PP reference.
 

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LEARN ABOUT DEBIAN

pperl

PPERL(1p)						User Contributed Perl Documentation						 PPERL(1p)

NAME

       PPerl - Make perl scripts persistent in memory

SYNOPSIS

	 $ pperl foo.pl

DESCRIPTION

       This program turns ordinary perl scripts into long running daemons, making subsequent executions extremely fast. It forks several processes
       for each script, allowing many processes to call the script at once.

       It works a lot like SpeedyCGI, but is written a little differently. I didn't use the SpeedyCGI codebase, because I couldn't get it to
       compile, and needed something ASAP.

       The easiest way to use this is to change your shebang line from:

	 #!/usr/bin/perl -w

       To use pperl instead:

	 #!/usr/bin/pperl -w

WARNINGS

       Like other persistent environments, this one has problems with things like BEGIN blocks, global variables, etc. So beware, and try checking
       the mod_perl guide at http://perl.apache.org/guide/ for lots of information that applies to many persistent perl environments.

Parameters
	 $ pperl <perl params> -- <pperl params> scriptname <script params>

       The perl params are sent to the perl binary the first time it is started up.  See perlrun for details.

       The pperl params control how pperl works. Try -h for an overview.

       The script params are passed to the script on every invocation. The script also gets any current environment variables, the current working
       directory, and everything on STDIN.

Killing
       In order to kill a currently running PPerl process, use:

	 pperl -- -k <scriptname>

       You need to make sure the path to the script is the same as when it was invoked.

       Alternatively look for a .pid file for the script in your tmp directory, and kill (with SIGINT) the process with that PID.

ENVIRONMENT

       pperl uses the PPERL_TMP_PATH environment variable to determine the directory where to store the files used for inter-process
       communication.  By default, the subdirectory .pperl of the user's home directory is used.

BUGS

       The process does not reload when the script or modules change.

       $^S is not represented identically with respect to perl, since your script will be run within an eval block

AUTHOR

       Matt Sergeant, matt@sergeant.org. Copyright 2001 MessageLabs Ltd.

SEE ALSO

       perl. perlrun.

perl v5.14.2							    2011-11-15								 PPERL(1p)
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