#!/usr/local/perl/5.10.0/bin/perl

use strict;
use warnings;

use POSIX;
use Data::Dumper;
$Data::Dumper::Useqq = 1;

my $inf;
my $sender_pid;

POSIX::sigaction(
           SIGINT,
           POSIX::SigAction->new(
               sub {
                   $inf = Dumper \@_;
                   $sender_pid = unpack "x16S", $_[2];     # <--
               },
               0,
               POSIX::SA_SIGINFO
           ),
       );

kill 'INT', $$;

print $inf;
print "Sender PID: $sender_pid\n";
print "Own PID:    $$\n";

__END__
$VAR1 = [
          "INT",
          {
            "code" => 0,
            "signo" => 2
          },
          "\2\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0RQ\0\0005\4\0\0\270\273}\0\0\0\0\0`\257i\0\0\0\0\0\3342E\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\370\25e\0\0\0\0\0\30 e\0\0\0\0\0\1\0\0\0\0\0\0\0\r\0\0\0\0\0\0\0\360b8\213\377\177\0\0\370b8\213\377\177\0\0\1\0\0\0\0\0\0\0\3IM\0\0\0\0\0"
        ];
Sender PID: 20818   (as we're sending the signal ourself, the sender is $$)
Own PID:    20818