strlen( $url_contents )
$ext = substr(strstr("test.test.php", '.'), 1);
http://us2.php.net/manual/en/function.strstr.php
strpos() is faster if you only want to see if substr exists...
$start_offset = strpos( $url_contents , $search_char , $offset );
strtolower()
addcslashes() returns a string with slashes added in front of chars...
ltrim() / rtrim() strips whitespace
implode() string fron an array
strip_tags() strips html & php tags from a string
If search and replace are arrays, then str_replace() takes a value from each array