'PHP's preg_match() and preg_match_all() functions

What do the preg_match() and preg_match_all() functions do and how can I use them?

phppreg-matchpreg-match-all


Solution 1:[1]

Both preg_match and preg_match_all functions in PHP use Perl compatible regular expressions.

You can watch this series to fully understand Perl compatible regular expressions: https://www.youtube.com/watch?v=GVZOJ1rEnUg&list=PLfdtiltiRHWGRPyPMGuLPWuiWgEI9Kp1w

preg_match($pattern, $subject, &$matches, $flags, $offset)

The preg_match function is used to search for a particular $pattern in a $subject string and when the pattern is found the first time, it stops searching for it. It outputs matches in the $matches, where $matches[0] will contain the text that matched the full pattern, $matches[1] will have the text that matched the first captured parenthesized sub-pattern, and so on.

Example of preg_match()

<?php
preg_match(
    "|<[^>]+>(.*)</[^>]+>|U",
    "<b>example: </b><div align=left>this is a test</div>",
    $matches
);

var_dump($matches);

Output: 

array(2) {
  [0]=>
  string(16) "<b>example: </b>"
  [1]=>
  string(9) "example: "
}

preg_match_all($pattern, $subject, &$matches, $flags)

The preg_match_all function searches for all the matches in a string and outputs them in a multi-dimensional array ($matches) ordered according to $flags. When no $flags value is passed, it orders results so that $matches[0] is an array of full pattern matches, $matches[1] is an array of strings matched by the first parenthesized sub-pattern, and so on.

Example of preg_match_all()

<?php
preg_match_all(
    "|<[^>]+>(.*)</[^>]+>|U",
    "<b>example: </b><div align=left>this is a test</div>",
    $matches
);

var_dump($matches);

Output: 

array(2) {
  [0]=>
  array(2) {
    [0]=>
    string(16) "<b>example: </b>"
    [1]=>
    string(36) "<div align=left>this is a test</div>"
  }
  [1]=>
  array(2) {
    [0]=>
    string(9) "example: "
    [1]=>
    string(14) "this is a test"
  }
}

Solution 2:[2]

A concrete example:

preg_match("/find[ ]*(me)/", "find me find   me", $matches):
$matches = Array(
    [0] => find me
    [1] => me
)

preg_match_all("/find[ ]*(me)/", "find me find   me", $matches):
$matches = Array(
    [0] => Array
        (
            [0] => find me
            [1] => find   me
        )

    [1] => Array
        (
            [0] => me
            [1] => me
        )
)

preg_grep("/find[ ]*(me)/", ["find me find    me", "find  me findme"]):
$matches = Array
(
    [0] => find me find    me
    [1] => find  me findme
)

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 Ronin
Solution 2

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