preg_match

Description
Syntax
Examples
Links

Description

The preg_match of PCRE for PHP perform a regular expression match.

Syntax

preg_match(
    string $pattern,
    string $subject,
    array &$matches = null,
    int $flags = 0,
    int $offset = 0
): int|false

Parameters

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:

Contant	Description
PREG_OFFSET_CAPTURE	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.
PREG_UNMATCHED_AS_NULL	Unmatched subpatterns are reported as NULL; otherwise they are reported as an empty string.

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). Alternatively, to avoid using substr(), use the \G assertion rather than the ^ anchor, or the A modifier instead, both of which work with the offset parameter.

<?

$pattern = "#php#";
$subject = "PHP stands for PHP: Hypertext Preprocessor";

$return = preg_match($pattern, $subject);

echo $return;

?>

2 · pattern subject · case-insensitive

<?

$pattern = "#php#i";
$subject = "PHP stands for PHP: Hypertext Preprocessor";

$return = preg_match($pattern, $subject);

echo $return;

?>

3 · matches

<?

$pattern = "#php#i";
$subject = "PHP stands for PHP: Hypertext Preprocessor";

preg_match($pattern, $subject, $matches);

print_r($matches);

?>

Array
(
    [0] => PHP
)

4 · flags · PREG_OFFSET_CAPTURE

<?

$pattern = "#(preg)(offset)(capture)#";
$subject = "pregoffsetcapture";
$flags = PREG_OFFSET_CAPTURE;

preg_match($pattern, $subject, $matches, $flags);

print_r($matches);

?>

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

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

    [2] => Array
        (
            [0] => offset
            [1] => 4
        )

    [3] => Array
        (
            [0] => capture
            [1] => 10
        )

)

5 · flags · PREG_UNMATCHED_AS_NULL

<?

$pattern = "#(preg)(unmatched)*(as)#";
$subject = "pregas";
$flags = PREG_UNMATCHED_AS_NULL;

preg_match($pattern, $subject, $matches1);
preg_match($pattern, $subject, $matches2, $flags);

var_export($matches1);
echo PHP_EOL;
var_export($matches2);

?>

array (
  0 => 'pregas',
  1 => 'preg',
  2 => '',
  3 => 'as',
)
array (
  0 => 'pregas',
  1 => 'preg',
  2 => NULL,
  3 => 'as',
)

6 · offset

<?

$pattern = "#offset#";
$subject = "offset offset offset";
$flags = PREG_OFFSET_CAPTURE;
$offset = 1;

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

print_r($matches);

?>

Array
(
    [0] => Array
        (
            [0] => offset
            [1] => 7
        )

)

7 · word boundary

<?

$pattern = "#\bweb\b#";
$subject1 = "PHP is the web scripting language of choice.";
$subject2 = "PHP is the website scripting language of choice.";

$return1 = preg_match($pattern, $subject1);
$return2 = preg_match($pattern, $subject2);

echo $return1 . PHP_EOL;
echo $return2;

?>

1
0

8 · named subpattern

<?

$pattern = "#(?<name>\w+): (?<digit>\d+)#";
$subject = "year: 2001";

preg_match($pattern, $subject, $matches);

print_r($matches);

?>

Array
(
    [0] => year: 2001
    [name] => year
    [1] => year
    [digit] => 2001
    [2] => 2001
)

9 · URL

<?

$pattern = "#^(?:https?://)?([^/]+)#i";
$subject = "https://sub.domain.com/";

preg_match($pattern, $subject, $matches);

print_r($matches);

$pattern = "#[^.]+\.[^.]+$#";
$subject = $matches[1];

preg_match($pattern, $subject, $matches);

print_r($matches);

?>

Array
(
    [0] => https://sub.domain.com
    [1] => sub.domain.com
)
Array
(
    [0] => domain.com
)