- var_dump: documentation ( source)
- str_replace: documentation ( source)
- preg_replace: documentation ( source)
<?php
$subject = "we went to see a ewe";
var_dump(str_replace(['e', 'w'], ['w', 'e'], $subject));
var_dump(str_replace([0 => 'e', 1 => 'w'], [0 => 'w', 1 => 'e'], $subject));
var_dump(preg_replace(['/e/', '/w/'], ['w', 'e'], $subject));
var_dump(preg_replace([0 => '/e/', 1 => '/w/'], [0 => 'w', 1 => 'e'], $subject));