What is preg_match_all in php?

[PHP 4, PHP 5, PHP 7, PHP 8]

preg_match_all — Perform a global regular expression match

Description

preg_match_all[
    string $pattern,
    string $subject,
    array &$matches = null,
    int $flags = 0,
    int $offset = 0
]: int|false

After the first match is found, the subsequent searches are continued on from end of the last match.

Parameters

The pattern to search for, as a string.

The input string.

Array of all matches in multi-dimensional array ordered according to 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]:

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.

The above example will output:

example: , 
this is a test
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].

The above example will output:

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

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.

The above example will output:

example: , example:
this is a test
, this is a test

If this flag is passed, for every occurring match the appendant string offset [in bytes] 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.

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 this flag is passed, unmatched subpatterns are reported as null; otherwise they are reported as an empty string.

If no order flag is given, PREG_PATTERN_ORDER is assumed.

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 [?

Example #2 Find matching HTML tags [greedy]

The above example will output:

matched: bold text
part 1: 
part 2: b
part 3: bold text
part 4: 

matched: click me
part 1: 
part 2: a
part 3: click me
part 4: 

Example #3 Using named subpattern

The above example will output:

Array
[
    [0] => Array
        [
            [0] => a: 1
            [1] => b: 2
            [2] => c: 3
        ]

    [name] => Array
        [
            [0] => a
            [1] => b
            [2] => c
        ]

    [1] => Array
        [
            [0] => a
            [1] => b
            [2] => c
        ]

    [digit] => Array
        [
            [0] => 1
            [1] => 2
            [2] => 3
        ]

    [2] => Array
        [
            [0] => 1
            [1] => 2
            [2] => 3
        ]

]

See Also

• PCRE Patterns
• preg_quote[] - Quote regular expression characters
• preg_match[] - Perform a regular expression match
• preg_replace[] - Perform a regular expression search and replace
• preg_split[] - Split string by a regular expression
• preg_last_error[] - Returns the error code of the last PCRE regex execution

buuh ¶

11 years ago

if you want to extract all {token}s from a string:



output:

Array
[
    [0] => Array
        [
            [0] => {token1}
            [1] => {token2}
        ]

]

Daniel Klein ¶

7 years ago

The code that john at mccarthy dot net posted is not necessary. If you want your results grouped by individual match simply use:

E.g.

mnc at u dot nu ¶

16 years ago

PREG_OFFSET_CAPTURE always seems to provide byte offsets, rather than character position offsets, even when you are using the unicode /u modifier.

phpnet at sinful-music dot com ¶

16 years ago

Here's some fleecy code to 1. validate RCF2822 conformity of address lists and 2. to extract the address specification [the part commonly known as 'email']. I wouldn't suggest using it for input form email checking, but it might be just what you want for other email applications. I know it can be optimized further, but that part I'll leave up to you nutcrackers. The total length of the resulting Regex is about 30000 bytes. That because it accepts comments. You can remove that by setting $cfws to $fws and it shrinks to about 6000 bytes. Conformity checking is absolutely and strictly referring to RFC2822. Have fun and email me if you have any enhancements!