find old debian packages after upgrade

find-old-debian-packages.php

<?php

/* yeah i know, php buuuuuh */

exec('apt-cache dumpavail | grep "Package:"  | awk \'{print $2}\' > packages.txt');
exec('dpkg -l | awk \'{print $2}\' > installed.txt');

$packages = file_get_contents('packages.txt');
$packages = str_replace("\r", '', $packages);
$packages = array_filter((array) explode("\n", $packages));


$installed = file_get_contents('installed.txt');
$installed = str_replace("\r", '', $installed);
$installed = array_filter((array) explode("\n", $installed));

foreach ($installed as $_pkg)
{
    $__pkg = array_filter((array)explode(':', $_pkg));
    $_pkg = array_shift($__pkg);
    unset($__pkg);
    if (!in_array($_pkg, $packages))
    {
        echo $_pkg;
        echo "\n";
    }
}