PID => [ PPID, COMMAND ]

##</code><code>##

#!/usr/bin/env perl

use strict;
use warnings;

my (%ps_data, @defunct_processes);

while (<DATA>) {
    next if $. == 1;  # Skip header: 'PID PPID COMMAND'
    chomp;
    my ($pid, $ppid, $cmd) = split ' ', $_, 3;
    $ps_data{$pid} = [$ppid => $cmd];
    push @defunct_processes, $pid if $cmd eq '<defunct>';
}

for my $pid (@defunct_processes) {
    my @trace;

    while ($pid >= 1) {
        push @trace, [$pid, @{$ps_data{$pid}}];
        $pid = $ps_data{$pid}[0];
    }
   
    printf "%4d  %4d  %s\n", @$_ for reverse @trace;
}

__DATA__
 PID  PPID  COMMAND
   0     0  sched
   1     0  /sbin/init
   7     0  vmtasks
 105     1  /usr/lib/saf/sac
7184     1  /usr/bin/java
7222     1  /usr/lib/utmpd
7501  6223  /usr/sbin/nscd
7507  7184  /bin/sh
7508  7507  /usr/bin/perl
7510  5044  /usr/bin/grep
7512  4333  /usr/bin/egrep
7515  7508  sh
7516  7515  <defunct>

##</code><code>##

   1     0  /sbin/init
7184     1  /usr/bin/java
7507  7184  /bin/sh
7508  7507  /usr/bin/perl
7515  7508  sh
7516  7515  <defunct>