preg_match
(PHP 4, PHP 5, PHP 7)
preg_match — Perform a regular expression match
Description
$pattern
, string $subject
[, array &$matches
[, int $flags
= 0
[, int $offset
= 0
]]] )
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 intosubject
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 ) )
-
PREG_UNMATCHED_AS_NULL
-
If this flag is passed, unmatched subpatterns are reported as
NULL
; otherwise they are reported as an empty string.<?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);
?>The above example will 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" }
-
-
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 passingsubstr($subject, $offset)
to preg_match() in place of the subject string, becausepattern
can 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 ) )
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.
Return Values
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.
Changelog
Version | Description |
---|---|
7.2.0 |
The PREG_UNMATCHED_AS_NULL is now supported for the
$flags parameter.
|
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>). |
Examples
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 )
Notes
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.
See Also
- PCRE Patterns
- preg_quote() - Quote regular expression characters
- preg_match_all() - Perform a global 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
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