PHP preg_match() Function

The preg_match function is used to perform a regular expression match.

Syntax

int preg_match ( string $pattern , string $subject [, array &$matches [, int $flags = 0 [, int $offset = 0 ]]] )

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

Parameter description:

$pattern: The pattern to search for, as a string.
$subject: The input string.
$matches: If the matches parameter is provided, it will be filled with the search results. $matches
$flags: flags can be set to the following flag values:
1. PREG_OFFSET_CAPTURE: If this flag is passed, for every occurrence of a match, the string offset (relative to the target string) will be appended. Note: This changes the array filled into the matches parameter, making each element an array where the 0th element is the matched string and the 1st element is the offset of that matched string in the target string subject.
offset: Usually, the search starts from the beginning of the target string. The optional parameter offset is used to specify starting the search from a certain position in the target string (in bytes).

Return Value

Returns the number of matches for pattern. Its value will be 0 (no match) or 1, because preg_match() stops searching after the first match. preg_match_all() is different; it continues searching subject until the end is reached. If an error occurs, preg_match() returns FALSE.

Examples

Find the text string "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 "The matching string php was found."; } else { echo "The matching string php was not found."; } ?>

The execution result is as follows:

查找到匹配的字符串 php。

Find the word "web"

<?php /*The \b in the pattern marks a word boundary, so only the standalone word "web" will be matched, and not * parts of a word such as "webbing" or "cobweb"*/ if (preg_match("/\bweb\b/i", "PHP is the web scripting language of choice.")) { echo "A matching string was found.\n"; } else { echo "No matching string was found.\n"; } if (preg_match("/\bweb\b/i", "PHP is the website scripting language of choice.")) { echo "A matching string was found.\n"; } else { echo "No matching string was found.\n"; } ?>

The execution result is as follows:

Matching string found.

Get the domain name from URL

<?php //Get the host name from the URL preg_match('@^(?:http://)?([^/]+)@i', "http://www.example.com/index.html", $matches); $host = $matches[1]; //Get the last two parts of the host name preg_match('/[^.]+\.[^.]+$/', $host, $matches); echo "domain name is: {$matches[0]}\n"; ?>

The execution result is as follows:

domain name is: example.com

Using Named Subgroups

<?php $str = 'foobar: 2008'; preg_match('/(?P<name>\w+): (?P<digit>\d+)/', $str, $matches); /*The following example works under PHP 5.2.2 (PCRE 7.0) or later; however, for backward compatibility, the above approach is the recommended syntax.*/ // preg_match('/(?<name>\w+): (?<digit>\d+)/', $str, $matches); print_r($matches); ?>

The execution result is as follows:

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

PHP Regular Expressions (PCRE)

Other Extensions