strings

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