Parameters

pattern

The pattern to search for, as a string.

subject

The input string.

matches

Array of all matches in multi-dimensional array ordered according to flags.

flags

Can be a combination of the following flags (note that it doesn't make sense to use PREG_PATTERN_ORDER together with PREG_SET_ORDER):

PREG_PATTERN_ORDER

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 subpattern, and so on.

<?php
preg_match_all("|<[^>]+>(.*)</[^>]+>|U",
    "<b>example: </b><div align=left>this is a test</div>",
    $out, PREG_PATTERN_ORDER);
echo $out[0][0] . ", " . $out[0][1] . "\n";
echo $out[1][0] . ", " . $out[1][1] . "\n";
?>

The above example will output:

<b>example: </b>, <div align=left>this is a test</div>
example: , this is a test

So, $out[0] contains array of strings that matched full pattern, and $out[1] contains array of strings enclosed by tags.

If the pattern contains named subpatterns, $matches additionally contains entries for keys with the subpattern name.

If the pattern contains duplicate named subpatterns, only the rightmost subpattern is stored in $matches[NAME].

<?php
preg_match_all(
    '/(?J)(?<match>foo)|(?<match>bar)/',
    'foo bar',
    $matches,
    PREG_PATTERN_ORDER
);
print_r($matches['match']);
?>

The above example will output:

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

PREG_SET_ORDER

Orders results so that $matches[0] is an array of first set of matches, $matches[1] is an array of second set of matches, and so on.

<?php
preg_match_all("|<[^>]+>(.*)</[^>]+>|U",
    "<b>example: </b><div align=\"left\">this is a test</div>",
    $out, PREG_SET_ORDER);
echo $out[0][0] . ", " . $out[0][1] . "\n";
echo $out[1][0] . ", " . $out[1][1] . "\n";
?>

The above example will output:

<b>example: </b>, example:
<div align="left">this is a test</div>, this is a test

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 value of matches into an array of arrays where every element is an array consisting of the matched string at offset 0 and its string offset into subject at offset 1.

<?php
preg_match_all('/(foo)(bar)(baz)/', 'foobarbaz', $matches, PREG_OFFSET_CAPTURE);
print_r($matches);
?>

The above example will output:

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

        )

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

        )

    [2] => Array
        (
            [0] => Array
                (
                    [0] => bar
                    [1] => 3
                )

        )

    [3] => Array
        (
            [0] => Array
                (
                    [0] => baz
                    [1] => 6
                )

        )

)

If no order flag is given, PREG_PATTERN_ORDER is assumed.

offset

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 (in bytes).

Note:

Using offset is not equivalent to passing substr($subject, $offset) to preg_match_all() in place of the subject string, because pattern can contain assertions such as ^, $ or (?<=x). See preg_match() for examples.