Useful Functions

Arrays

array_key_exists($key, $array)

Strings

$len = strlen("text");

$pos = strpos("text", "x");

str_replace("old", "new", "text");

Files

file_exists($filename)

$text = file_get_contents($filename);

$root = simplexml_load_file($filename);

Path info:

$name_part = pathinfo($filename, PATHINFO_FILENAME);
$ext_part = pathinfo($filename, PATHINFO_EXTENSION);

$size_array = getimagesize($filename);