#!/usr/bin/perl

if (my $pid = fork()) {

    # kill process group after timeout
    sleep 3;
    show_procs();
    kill -9, $pid;  # negative signal number kills group
    wait;
    print "killed children\n";
    show_procs();   # show remaining processes

    # ...
    
} elsif (defined $pid) {
    
    setpgrp;  # create new process group
    
    # run something (consisting of several processes) that takes a while
    exec 'find / | grep foo';

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

sub show_procs {
    system "ps Tf -o pid,ppid,pgrp,sid,cmd";
}

__END__
$ ./841709.pl
  PID  PPID  PGRP   SID CMD
12046 12044 12046 12046 bash -rcfile .bashrc
 3881 12046  3881 12046  \_ /usr/bin/perl ./841709.pl
 3882  3881  3882 12046      \_ sh -c find / | grep foo
 3883  3882  3882 12046      |   \_ find /
 3884  3882  3882 12046      |   \_ grep foo
 3885  3881  3881 12046      \_ ps Tf -o pid,ppid,pgrp,sid,cmd
killed children
  PID  PPID  PGRP   SID CMD
12046 12044 12046 12046 bash -rcfile .bashrc
 3881 12046  3881 12046  \_ /usr/bin/perl ./841709.pl
 3886  3881  3881 12046      \_ ps Tf -o pid,ppid,pgrp,sid,cmd