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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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build-lives-rfx-plugin

build-lives-rfx-plugin(1)				      General Commands Manual					 build-lives-rfx-plugin(1)

NAME

       build-lives-rfx-plugin - builds rendered effects for LiVES

SYNOPSIS

       build-lives-rfx-plugin script_name [plugin_dir] -get section file

DESCRIPTION

       This perl script is used by LiVES to compile an RFX (rendered effect) plugin for LiVES. It is generally called from build-lives-rfx-plugin-
       multi for a script which has a language code representing LiVES-perl. The script_name must be  the  full  (absolute)  path  to  the  plugin
       script,	and  plugin_dir  can  be  used to specify the output directory where the compiled plugin should be generated. If plugin_dir is not
       defined then /tmp is assumed.

       The second variant with -get is used to print out a script section from a plugin script to stdout. It is generally only used internally	by
       LiVES.

       Return values The script returns the following values

       0 - success 1 - the value of a trigger was greater than the number of parameters 2 - a value could not be read from the script file 3 - the
       language code of the plugin script was not equivalent to LiVES-perl 4 - the API version level of the plugin script  was	invalid  5  -  the
       <define> section was missing from the plugin script

SEE ALSO

       build-lives-rfx-plugin-multi(1), lives(1)

AUTHOR

       Gabriel Finch a.k.a Salsaman (salsaman@xs4all.nl)

								    May 9 2010						 build-lives-rfx-plugin(1)
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