PHP preg_match() Function

Use a regular expression to do a case-insensitive search for "w3schools" in a string:

<?php
$str = "Visit W3Schools";
$pattern = "/w3schools/i";
echo preg_match($pattern, $str);
?>

Definition and Usage

The preg_match() function returns whether a match was found in a string.

preg_match(pattern, input, matches, flags, offset)

Parameter	Description
pattern	Required. Contains a regular expression indicating what to search for
input	Required. The string in which the search will be performed
matches	Optional. The variable used in this parameter will be populated with an array containing all of the matches that were found
flags	Optional. A set of options that change how the matches array is structured: `PREG_OFFSET_CAPTURE` - When this option is enabled, each match, instead of being a string, will be an array where the first element is a substring containing the match and the second element is the position of the first character of the substring in the input. `PREG_UNMATCHED_AS_NULL` - When this option is enabled, unmatched subpatterns will be returned as NULL instead of as an empty string.
offset	Optional. Defaults to 0. Indicates how far into the string to begin searching. The preg_match() function will not find matches that occur before the position given in this parameter

Return Value:	Returns 1 if a match was found, 0 if no matches were found and false if an error occurred
PHP Version:	4+
Changelog:	PHP 7.2 - Added the PREG_UNMATCHED_AS_NULL flag PHP 5.3.6 - The function returns false when the offset is longer than the length of the input PHP 5.2.2 - Named subpatterns can use the (?'name') and (? <name>) syntax in addition to the previous (?P<name>)

Use PREG_OFFSET_CAPTURE to find the position in the input string in which the matches were found:

<?php
$str = "Welcome to W3Schools";
$pattern = "/w3schools/i";
preg_match($pattern, $str, $matches, PREG_OFFSET_CAPTURE);
print_r($matches);
?>