#!/usr/bin/env perl

use strict;
use warnings;

use constant {
    CHILD            => 0,
    PARENT           => 1,
    GRANDPARENT      => 2,
    GREATGRANDPARENT => 3,
};

my $table = [
    { pid => 0,     ppid => 0,     cmd => 'root' },
    { pid => 603,   ppid => 0,     cmd => 'cron_parent' },
    { pid => 18421, ppid => 603,   cmd => 'cron_child' },
    { pid => 18423, ppid => 18421, cmd => 'sh_mon' },
    { pid => 18425, ppid => 18423, cmd => 'sh_kit' },
    { pid => 18444, ppid => 18425, cmd => 'java' },
    { pid => 28421, ppid => 603,   cmd => 'cron_child' },
    { pid => 28423, ppid => 18421, cmd => 'sh_mon' },
    { pid => 28425, ppid => 18423, cmd => 'sh_kit' },
    { pid => 28444, ppid => 18425, cmd => 'java' },
    { pid => 28445, ppid => 18425, cmd => 'java' },
    { pid => 99999, ppid => 18421, cmd => 'java' },
    { pid => 2,     ppid => 1,     cmd => 'unwanted' },
];

my $ancestry = 3;
my %tree; 

{
    my %all;

    for (@$table) {
        $all{$_->{pid}} = $_;
        $tree{$_->{pid}} = [ $_ ] if $_->{cmd} =~ /java/;
    }

    for my $child (keys %tree) {
        my $ppid = $all{$child}{ppid};

        for (1 .. $ancestry) {
            push @{$tree{$child}}, {%{$all{$ppid}}};
            $ppid = $all{$ppid}{ppid};
        }
    }
}

use Data::Dump;
print "*** All parents ***\n";
dd [ map { $tree{$_}[PARENT] } sort keys %tree ];

print "*** 18444 grandparent ***\n";
dd $tree{18444}[GRANDPARENT];

print "*** 18444 greatgrandparent ***\n";
dd $tree{18444}[GREATGRANDPARENT];

print "*** All ancestries ***\n";
dd \%tree;