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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 OSX

findbin

FindBin(3pm)						 Perl Programmers Reference Guide					      FindBin(3pm)

NAME

       FindBin - Locate directory of original perl script

SYNOPSIS

	use FindBin;
	use lib "$FindBin::Bin/../lib";

	or

	use FindBin qw($Bin);
	use lib "$Bin/../lib";

DESCRIPTION

       Locates the full path to the script bin directory to allow the use of paths relative to the bin directory.

       This allows a user to setup a directory tree for some software with directories "<root>/bin" and "<root>/lib", and then the above example
       will allow the use of modules in the lib directory without knowing where the software tree is installed.

       If perl is invoked using the -e option or the perl script is read from "STDIN" then FindBin sets both $Bin and $RealBin to the current
       directory.

EXPORTABLE VARIABLES

	$Bin	     - path to bin directory from where script was invoked
	$Script      - basename of script from which perl was invoked
	$RealBin     - $Bin with all links resolved
	$RealScript  - $Script with all links resolved

KNOWN ISSUES

       If there are two modules using "FindBin" from different directories under the same interpreter, this won't work. Since "FindBin" uses a
       "BEGIN" block, it'll be executed only once, and only the first caller will get it right. This is a problem under mod_perl and other
       persistent Perl environments, where you shouldn't use this module. Which also means that you should avoid using "FindBin" in modules that
       you plan to put on CPAN. To make sure that "FindBin" will work is to call the "again" function:

	 use FindBin;
	 FindBin::again(); # or FindBin->again;

       In former versions of FindBin there was no "again" function. The workaround was to force the "BEGIN" block to be executed again:

	 delete $INC{'FindBin.pm'};
	 require FindBin;

AUTHORS

       FindBin is supported as part of the core perl distribution. Please send bug reports to <perlbug@perl.org> using the perlbug program
       included with perl.

       Graham Barr <gbarr@pobox.com> Nick Ing-Simmons <nik@tiuk.ti.com>

COPYRIGHT

       Copyright (c) 1995 Graham Barr & Nick Ing-Simmons. All rights reserved.	This program is free software; you can redistribute it and/or
       modify it under the same terms as Perl itself.

perl v5.16.2							    2012-10-11							      FindBin(3pm)
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