<?php

$string1 = 'http://2.2.2.2/~machinehost/deployment_folder/';
$string2 = '/~machinehost/deployment_folder/users/bob/settings';

$split = str_split($string2);

$needle = '';
$matches = array();
foreach($split as $needleAppend) {
    if (!empty($needle)) {
        if (strpos($string1, $needle) === false) {
            $needle = '';
        } else {
            $matches[] = $needle;
        }
    }
    $needle = empty($needle) ? $needleAppend : $needle . $needleAppend;
}

function sortByLength($a,$b) {
    return strlen($b)-strlen($a);
}

usort($matches, 'sortByLength');
$largestString = array_shift($matches);
$remainder = substr($string2, strlen($largestString));

var_dump($remainder);