preg_match

Description

Searches subject for a match to the regular expression given in pattern.

Parameters

pattern

The pattern to search for, as a string.

subject

The input string.

matches

If matches is provided, then it is filled with the results of search. $matches[0] will contain the text that matched the full pattern, $matches[1] will have the text that matched the first captured parenthesized subpattern, and so on.

flags

flags can be a combination of the following flags:

PREG_OFFSET_CAPTURE

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

phpCopy

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

The above example will output:

output

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

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

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

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

)

PREG_UNMATCHED_AS_NULL

If this flag is passed, unmatched subpatterns are reported as null and are always included in the results (including trailing ones). Without this flag, unmatched subpatterns that are followed by a matched subpattern are reported as an empty string, while trailing unmatched subpatterns are omitted from the results entirely.

phpCopy

<?php
preg_match('/(a)(b)*(c)/', 'ac', $matches);
var_dump($matches);
preg_match('/(a)(b)*(c)/', 'ac', $matches, PREG_UNMATCHED_AS_NULL);
var_dump($matches);

// Trailing unmatched subpatterns:
preg_match('/(a)(b)?(c)?/', 'a', $matches);
var_dump($matches);
preg_match('/(a)(b)?(c)?/', 'a', $matches, PREG_UNMATCHED_AS_NULL);
var_dump($matches);
?>

The above example will output:

output

array(4) {
  [0]=>
  string(2) "ac"
  [1]=>
  string(1) "a"
  [2]=>
  string(0) ""
  [3]=>
  string(1) "c"
}
array(4) {
  [0]=>
  string(2) "ac"
  [1]=>
  string(1) "a"
  [2]=>
  NULL
  [3]=>
  string(1) "c"
}
array(2) {
  [0]=>
  string(1) "a"
  [1]=>
  string(1) "a"
}
array(4) {
  [0]=>
  string(1) "a"
  [1]=>
  string(1) "a"
  [2]=>
  NULL
  [3]=>
  NULL
}

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() in place of the subject string, because pattern can contain assertions such as ^, $ or (?<=x). Compare:

phpCopy

<?php
$subject = "abcdef";
$pattern = '/^def/';
preg_match($pattern, $subject, $matches, PREG_OFFSET_CAPTURE, 3);
print_r($matches);
?>

The above example will output:

output

Array
(
)

while this example

phpCopy

<?php
$subject = "abcdef";
$pattern = '/^def/';
preg_match($pattern, substr($subject,3), $matches, PREG_OFFSET_CAPTURE);
print_r($matches);
?>

will produce

output

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

)

Alternatively, to avoid using substr(), use the \G assertion rather than the ^ anchor, or the A modifier; both of which do not work with the offset parameter.

Return Values

preg_match() returns 1 if the pattern matches given subject, 0 if it does not,Falseforfailure.

Falseproblem

Errors/Exceptions Warning

Changelog

Examples

Find the string of text "php"

<?php
// The "i" after the pattern delimiter indicates a case-insensitive search
if (preg_match("/php/i", "PHP is the web scripting language of choice.")) {
    echo "A match was found.";
} else {
    echo "A match was not found.";
}
?>

Find the word "web"

<?php
/* The \b in the pattern indicates a word boundary, so only the distinct
 * word "web" is matched, and not a word partial like "webbing" or "cobweb" */
if (preg_match("/\bweb\b/i", "PHP is the web scripting language of choice.")) {
    echo "A match was found.";
} else {
    echo "A match was not found.";
}

echo "\n";

if (preg_match("/\bweb\b/i", "PHP is the website scripting language of choice.")) {
    echo "A match was found.";
} else {
    echo "A match was not found.";
}
?>

Getting the domain name out of a URL

<?php
// get host name from URL
preg_match('@^(?:http://)?([^/]+)@i',
    "http://www.php.net/index.html", $matches);
$host = $matches[1];

// get last two segments of host name
preg_match('/[^.]+\.[^.]+$/', $host, $matches);
echo "domain name is: {$matches[0]}\n";
?>

The above example will output:

domain name is: php.net

Using named subpattern

<?php

$str = 'foobar: 2008';

preg_match('/(?P<name>\w+): (?P<digit>\d+)/', $str, $matches);

/* Alternative */
// preg_match('/(?<name>\w+): (?<digit>\d+)/', $str, $matches);

print_r($matches);

?>

The above example will output:

Array
(
    [0] => foobar: 2008
    [name] => foobar
    [1] => foobar
    [digit] => 2008
    [2] => 2008
)

Notes

See Also

• PCRE Patterns
• preg_quote()
• preg_match_all()
• preg_replace()
• preg_split()
• preg_last_error()
• preg_last_error_msg()