#!/usr/bin/perl

# https://perlmonks.org/?node_id=1228107

use strict;
use warnings;

my $firsthash =
  {
  "./bye_world.pl"         => { data => 4, pid => { 7302 => 2 } },
  "./hello_world.pl"       => { data => 4, pid => { 7287 => 2 } },
  "/perl/5.14.1/strict.pm" => { data => 6, pid => { 7287 => 1, 7302 => 1 } },
  "/some_text.txt/"        => { data => 2, pid => { 7287 => 1, 7302 => 1 } },
  };

my $secondhash =
  {
  7287 => { name => "./hello_world.pl", parent => "###" },
  7299 => { name => "echo Hello World ", parent => 7287 },
  7302 => { name => "./bye_world.pl", parent => 7287 },
  7305 => { name => "echo Bye World ", parent => 7302 },
  };

sub parents
  {
  my ($name, $pid) = @_;
  exists $secondhash->{$pid} or return '';
  my $secondname = $secondhash->{$pid}{name};
  return ($name ne $secondname and ",$secondname") .
    parents($secondname, $secondhash->{$pid}{parent});
  }

for my $name ( keys %$firsthash )
  {
  for my $pid ( keys %{ $firsthash->{$name}{pid} } )
    {
    print $name, parents($name, $pid), "\n";
    }
  }