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PHP preg_match_all() Function

❮ PHP RegExp Reference


Find all occurrences of "ain" in a string:

$str = "The rain in SPAIN falls mainly on the plains.";
$pattern = "/ain/i";
if(preg_match_all($pattern, $str, $matches)) {
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Definition and Usage

The preg_match_all() function returns the number of matches of a pattern that were found in a string and populates a variable with the matches that were found.


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

Parameter Values

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.

One of the following structures may be selected:
  • PREG_PATTERN_ORDER - Default. Each element in the matches array is an array of matches from the same grouping in the regular expression, with index 0 corresponding to matches of the whole expression and the remaining indices for subpattern matches.
  • PREG_SET_ORDER - Each element in the matches array contains matches of all groupings for one of the found matches in the string.
Any number of the following options may be applied:
  • 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

Technical Details

Return Value: Returns the number of matches found or false if an error occurred
PHP Version: 4+
Changelog: PHP 7.2 - Added the PREG_UNMATCHED_AS_NULL flag

PHP 5.4 - The matches parameter became optional

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>)

More Examples


Use PREG_PATTERN_ORDER to set the structure of the matches array. In this example, each element in the matches array has all of the matches for one of the groupings of the regular expression.

$str = "abc ABC";
$pattern = "/((a)b)(c)/i";
if(preg_match_all($pattern, $str, $matches, PREG_PATTERN_ORDER)) {
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❮ PHP RegExp Reference