strlen($s) returns an integer denoting the length of $s. str_word_count($s1[,$i=0[,$s2]]) returns the number of words in $s1. If $i is 1, an array containing all the words will be returned. If $i is 2, an associative array will be returned, where the key is the character position and the value is the word itself. $s2 is a list of additional characters which will be considered as ‘word’. substr_count($s1, $s2 [,$i1[,$i2]]) returns the no. of times $s2 is found in $s1. $i1 is the offset of where to start the counting. $i2 is the maximum length after the specified offset to search for the substring. count_chars($s[,$i=0]) counts the no. of times every byte value (from 0 to 255) is found in $s. If $i is 0, it gives an array with the byte-value as key and the frequency as value. $i=1 is same as $i=0, but it only lists byte-values occurring at least once. $i=2 is the same as $i=0 but it only lists byte-values occurring zero time. $i=3 returns a string of all unique characters. $i=4 returns a string of all not used characters.