#!/usr/bin/perl -w
use strict;
sub ps { system "ps Tf -o pid,ppid,pgrp,sid,cmd"; }
$SIG{CHLD} = 'IGNORE';
my $snoop = fork();
if ( $snoop == 0 ){
    setpgrp;
    system("sleep 20 ;");
    exit;
}
ps();
sleep 1;

print  "PID:  $snoop\n";
printf "PGRP: %d\n", getpgrp($snoop);
kill -1, getpgrp($snoop);
ps();

__END__
  PID  PPID  PGRP   SID CMD
 2360  2358  2360  2360 bash -rcfile .bashrc
19537  2360 19537  2360  \_ /usr/bin/perl -w ./964597.pl
19538 19537 19538  2360      \_ /usr/bin/perl -w ./964597.pl
19540 19538 19538  2360      |   \_ sh -c sleep 20 ;
19541 19540 19538  2360      |       \_ sleep 20
19539 19537 19537  2360      \_ ps Tf -o pid,ppid,pgrp,sid,cmd
PID:  19538
PGRP: 19538
  PID  PPID  PGRP   SID CMD
 2360  2358  2360  2360 bash -rcfile .bashrc
19537  2360 19537  2360  \_ /usr/bin/perl -w ./964597.pl
19542 19537 19537  2360      \_ ps Tf -o pid,ppid,pgrp,sid,cmd