(PHP 4, PHP 5, PHP 7)
preg_match — Perform a regular expression match
$pattern
, string $subject
[, array &$matches
[, int $flags = 0
[, int $offset = 0
]]] )
Searches subject for a match to the regular
expression given in pattern.
patternThe pattern to search for, as a string.
subjectThe 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 the following flag:
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 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('/(foo)(bar)(baz)/', 'foobarbaz', $matches, PREG_OFFSET_CAPTURE);
print_r($matches);
?>
The above example will 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
)
)
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
offsetis not equivalent to passing substr($subject, $offset) to preg_match() in place of the subject string, becausepatterncan contain assertions such as ^, $ or (?<=x). Compare:<?php
$subject = "abcdef";
$pattern = '/^def/';
preg_match($pattern, $subject, $matches, PREG_OFFSET_CAPTURE, 3);
print_r($matches);
?>The above example will output:
Array ( )while this example
<?php
$subject = "abcdef";
$pattern = '/^def/';
preg_match($pattern, substr($subject,3), $matches, PREG_OFFSET_CAPTURE);
print_r($matches);
?>will produce
Array ( [0] => Array ( [0] => def [1] => 0 ) )
preg_match() returns 1 if the pattern
matches given subject, 0 if it does not, or FALSE
if an error occurred.
This function may
return Boolean FALSE, but may also return a non-Boolean value which
evaluates to FALSE. Please read the section on Booleans for more
information. Use the ===
operator for testing the return value of this
function.
| Version | Description |
|---|---|
| 5.3.6 |
Returns FALSE if offset is higher than
subject length.
|
| 5.2.2 | Named subpatterns now accept the syntax (?<name>) and (?'name') as well as (?P<name>). Previous versions accepted only (?P<name>). |
Example #1 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.";
}
?>
Example #2 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.";
}
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.";
}
?>
Example #3 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
Example #4 Using named subpattern
<?php
$str = 'foobar: 2008';
preg_match('/(?P<name>\w+): (?P<digit>\d+)/', $str, $matches);
/* This also works in PHP 5.2.2 (PCRE 7.0) and later, however
* the above form is recommended for backwards compatibility */
// 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
)
Do not use preg_match() if you only want to check if one string is contained in another string. Use strpos() instead as it will be faster.