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preg_match
Perform a regular expression match
(PHP 4, PHP 5)
int preg_match ( string pattern, string subject [, array &matches [, int flags [, int offset]]] )
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 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 return value
in an array where every element is an array consisting of the matched
string at index
0and its string offset into subject at index1.
- 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:<?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
)
)
Return Values
preg_match() returns the number of times
pattern matches. That will be either 0 times
(no match) or 1 time because preg_match() will stop
searching after the first match. preg_match_all()
on the contrary will continue until it reaches the end of
subject.
preg_match() returns FALSE if an error occurred.
ChangeLog
| Version | Description |
|---|---|
| 4.3.3 | The offset parameter was added |
| 4.3.0 |
The PREG_OFFSET_CAPTURE flag was added
|
| 4.3.0 | The flags parameter was added |
Examples
Example 1718. 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 1719. 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 1720. 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
Notes
Do not use preg_match() if you only want to check if one string is contained in another string. Use strpos() or strstr() instead as they will be faster.