Return part of a string (PHP 3, PHP 4, PHP 5)

string substr ( string string, int start [, int length] )

substr() returns the portion of string specified by the start and length parameters.

If start is non-negative, the returned string will start at the start'th position in string, counting from zero. For instance, in the string 'abcdef', the character at position 0 is 'a', the character at position 2 is 'c', and so forth.

(copia / incolla della doc PHP, una piccola lettura è sempre utile...)