http://phpsnips.com/603/Escape-user-input-before-preg_replace#.VBG_A_mSySo Sometimes you need to do preg_replace on user input. Don't forget to escape all special characters or you'll get funny results.

escape_user_input_before_preg_replace.php

<?php 
$input = str_replace(array('^', '.', '|', '(', ')', '[', ']', '*', '+', '?', '{', '}', '$' ),  
        array('\^', '\.', '\|', '\(', '\)', '\[', '\]', '\*', '\+', '\?', '\{', '\}', '\$' ), $input);