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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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IO::Async::PID(3pm)					User Contributed Perl Documentation				       IO::Async::PID(3pm)

NAME
"IO::Async::PID" - event callback on exit of a child process SYNOPSIS
use IO::Async::PID; use POSIX qw( WEXITSTATUS ); use IO::Async::Loop; my $loop = IO::Async::Loop->new; my $kid = $loop->fork( code => sub { print "Child sleeping.. "; sleep 10; print "Child exiting "; return 20; }, ); print "Child process $kid started "; my $pid = IO::Async::PID->new( pid => $kid, on_exit => sub { my ( $self, $exitcode ) = @_; printf "Child process %d exited with status %d ", $self->pid, WEXITSTATUS($exitcode); }, ); $loop->add( $pid ); $loop->run; DESCRIPTION
This subclass of IO::Async::Notifier invokes its callback when a process exits. For most use cases, a IO::Async::Process object provides more control of setting up the process, connecting filehandles to it, sending data to and receiving data from it. EVENTS
The following events are invoked, either using subclass methods or CODE references in parameters: on_exit $exitcode Invoked when the watched process exits. PARAMETERS
The following named parameters may be passed to "new" or "configure": pid => INT The process ID to watch. Must be given before the object has been added to the containing "IO::Async::Loop" object. on_exit => CODE CODE reference for the "on_exit" event. Once the "on_exit" continuation has been invoked, the "IO::Async::PID" object is removed from the containing "IO::Async::Loop" object. METHODS
$process_id = $pid->pid Returns the underlying process ID $pid->kill( $signal ) Sends a signal to the process AUTHOR
Paul Evans <leonerd@leonerd.org.uk> perl v5.14.2 2012-10-24 IO::Async::PID(3pm)
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