#!/usr/bin/perl

my $sid = getppid;  # for the 'ps' process selection only

if (my $pid = fork()) {
    sleep 1; # wait somewhat until tree of children is set up
    # show related processes
    system "ps f -s $sid -o pid,ppid,pgrp,sid,cmd";

    # kill process group after timeout
    sleep 10;
    kill -9, $pid;
    wait;
    print "killed children\n";

    # show remaining processes
    system "ps f -s $sid -o pid,ppid,pgrp,sid,cmd";
    
    # do something else...
    sleep 10;
    
} elsif (defined $pid) {
    # create new process group
    setpgrp;
    # run something (consisting of several processes) that hangs
    system 'bash -c "cat; echo"';
    exit;

} else {
    die "couldn't fork";
}

##</code><code>##

$ ./698259.pl
  PID  PPID  PGRP   SID CMD
 2963  2960  2963  2963 bash
 4074  2963  4074  2963  \_ /usr/bin/perl ./698259.pl
 4075  4074  4075  2963      \_ /usr/bin/perl ./698259.pl
 4076  4075  4075  2963      |   \_ bash -c cat; echo
 4077  4076  4075  2963      |       \_ cat
 4078  4074  4074  2963      \_ ps f -s 2963 -o pid,ppid,pgrp,sid,cmd
killed children
  PID  PPID  PGRP   SID CMD
 2963  2960  2963  2963 bash
 4074  2963  4074  2963  \_ /usr/bin/perl ./698259.pl
 4079  4074  4074  2963      \_ ps f -s 2963 -o pid,ppid,pgrp,sid,cmd