preg_match Perform a regular expression match intpreg_match stringpattern stringsubject arraymatches intflags intoffset Searches subject for a match to the regular expression given in pattern. If matches is provided, then it is filled with the results of search. $matches[0] will contain the text that matched the full pattern, $matches[1] will have the text that matched the first captured parenthesized subpattern, and so on. flags can be the following flag: PREG_OFFSET_CAPTURE If this flag is passed, for every occurring match the appendant string offset will also be returned. Note that this changes the return value in an array where every element is an array consisting of the matched string at offset 0 and its string offset into subject at offset 1. This flag is available since PHP 4.3.0 . The flags parameter is available since PHP 4.3.0. Normally, the search starts from the beginning of the subject string. The optional parameter offset can be used to specify the alternate place from which to start the search. The offset parameter is available since PHP 4.3.3. Using offset is not equivalent to passing substr($subject, $offset) to preg_match in place of the subject string, because pattern can contain assertions such as ^, $ or (?<=x). Compare: ]]> &example.outputs; while this example ]]> will produce Array ( [0] => def [1] => 0 ) ) ]]> preg_match returns the number of times pattern matches. That will be either 0 times (no match) or 1 time because preg_match will stop searching after the first match. preg_match_all on the contrary will continue until it reaches the end of subject. preg_match returns &false; if an error occurred. Do not use preg_match if you only want to check if one string is contained in another string. Use strpos or strstr instead as they will be faster. ]]> ]]> ]]> &example.outputs; See also preg_match_all, preg_replace, and preg_split.