PHP Regular Expression subpatterns
Description
Parentheses inside regular expressions define subpatterns that should be matched individually.
Subpatterns allow you to match very specific criteria.
For example, "(I|You) like (PHP|Java)" would match
- "I like PHP",
- "I like Java",
- "You like PHP", and
- "You like Java".
Syntax
() creates subpatterns.
Example 1
The following table shows a list of regular expressions using parentheses, and whether or not a match is made.
| Regexp | Result |
|---|---|
| print preg_match("/(PHP|Mac OS X)/","PHP") | True |
| print preg_match("/(PHP|Mac OS X){2}/", "Mac OS X PHP") | True |
| print preg_match("/(PHP|Mac OS X){2}/","Mac OS X PHP") | False; there's a space in there, which is not part of the regexp |
| preg_match("/P(HP|ython)/","Python") | True |
| preg_match("/Windows ([0-9][0-9]+|Me|XP)/", "Windows 2000") | True; matches Windows 95, Windows 98, Windows 2000, 2003, Me, and XP |
| preg_match("/Windows (([0-9][0-9]+|Me|XP)|Codename (Vista|7))/","Windows Codename Vista") | True; |
Use Subpatterns to Group Patterns
We can use quantifiers (such as * and ?) to match the whole subpattern a certain number of times. For example:
<?PHP
echo preg_match( "/(row,? )+your boat/", "row, row, row your boat" );
?>
The subpattern in this regular expression is "(row,?)". The letters 'r', 'o', and 'w', followed by either zero or one comma, followed by a space character.
This subpattern is matched at least one time because of the following + quantifier.
We can retrieve the individual subpattern matches in the matches array passed to preg_match().
The first element of the array contains the entire matched text as usual, and each subsequent element contains any matched subpatterns:
<?PHP/* ww w .ja v a 2 s . c o m*/
preg_match( "/(\d+\/\d+\/\d+) (\d+\:\d+.+)/", "7/18/2013 9:21AM", $matches );
echo $matches[0] . "\n"; // Displays "7/18/2013 9:21AM"
echo $matches[1] . "\n"; // Displays "7/18/2013"
echo $matches[2] . "\n"; // Displays "9:21AM"
?>