What is preg_match function?
If you want to know whether a string consists of a sub string that matches with a regular expression pattern or you want to know the sub string’s position in the string if it exists, then use preg_match() function. After finding the first match, this function stops further searching.
Syntax:
preg_match(pattern, subject, matches flags, offset)
Parameters:
pattern (Mandatory): This parameter is a regular expression that you’ll search in the “subject” parameter to find any match (Check Example 1).
subject (Mandatory): This is the main string where you’ll find match (Check Example 1).
matches (Optional): If any match found, this parameter stores search result as an array.
- matches[0]: It contains string found in the “subject” parameter that matches the full pattern (Check example 2).
- matches[1]: If there are groups in the regular expression, this element contains the first captured group’s (or first captured parenthesized pattern’s) result (Check example 2).
- matches[2]: If there are groups in the regular expression, this element contains the second captured group’s (or second captured parenthesized pattern’s) result (Check example 2).
- matches[3]: and, so on.
flags (Optional): you can use two values (PREG_OFFSET_CAPTURE and PREG_UNMATCHED_AS_NULL) as flags to return different values from the function-
- PREG_OFFSET_CAPTURE: If you use this, the function returns each match as an array whether the “pattern” parameter has groups (Check example 3) or not (Check example 4). Each array has two elements – first element is the matching string found in the “subject” parameter and the second element is the matching position in the “subject” parameter.
- PREG_UNMATCHED_AS_NULL: If you use this, the function returns NULL for each unmatched group used in the “pattern” parameter (Check example 5).
offset (Optional): Instead of starting search from the beginning of the “subject” parameter, if you want to start it from a specific position, mention by this “offset” parameter. (Check example 6).
Return Values:
- It returns 1 if match found (Check example 7).
- It returns 0 if no match found (Check example 8).
- It returns FALSE if an error occurred.
Examples:
Example 1:
<pre>
<?php
$pattern = '/function/';
$str = "Learning PHP built-in functions make development easier.";
if (preg_match($pattern, $str)) {
echo "Match found.";
}else{
echo "Match not found.";
}
?>
</pre>
Output:
Match found.
Explanation:
Example 2:
<pre>
<?php
$pattern = '/(PHP) (built-in)/';
$str = "Learn PHP built-in functions.";
if (preg_match($pattern, $str, $matches)) {
print_r($matches);
}
?>
</pre>
Output:
Array(
[0] => PHP built-in
[1] => PHP
[2] => built-in
)
Explanation:
Example 3:
<pre>
<?php
$pattern = '/(PHP) (built-in)/';
$str = "Learn PHP built-in functions.";
if (preg_match($pattern, $str, $matches, PREG_OFFSET_CAPTURE)) {
print_r($matches);
}
?>
</pre>
Output:
Array
(
[0] => Array
(
[0] => PHP built-in
[1] => 6
)
[1] => Array
(
[0] => PHP
[1] => 6
)
[2] => Array
(
[0] => built-in
[1] => 10
)
)
Explanation:
Example 4:
<pre>
<?php
$pattern = '/PHP/';
$str = "Let's Learn PHP";
if (preg_match($pattern, $str, $matches, PREG_OFFSET_CAPTURE)) {
print_r($matches);
}
?>
Output:
Array(
[0] => Array
(
[0] => PHP
[1] => 12
)
)
Explanation:
Example 5:
<pre>
<?php
preg_match('/(built)*(function)/', 'PHP built-in function', $matches, PREG_UNMATCHED_AS_NULL);
var_dump($matches);
?>
</pre>
Output:
array(3) {
[0]=> string(8) “function”
[1]=> NULL
[2]=> string(8) “function”
}
Explanation:
Example 6:
<pre>
<?php
$pattern = '/learn/';
$str = "Do learn PHP built-in functions.";
if (preg_match($pattern, $str, $matches, PREG_OFFSET_CAPTURE, 4)) {
print_r($matches);
}else{
echo "Match not found";
}
?>
Output:
Match not found
Explanation:
Example 7:
<?php
$pattern = '/PHP/';
$str = "PHP built-in functions.";
$return_val = preg_match($pattern, $str);
echo $return_val;
?>
Output:
1
Explanation:
Example 8:
<?php
$pattern = '/JavaScript/';
$str = "PHP built-in functions.";
$return_val = preg_match($pattern, $str);
echo $return_val;
?>
Output:
0
Explanation:
PHP Version Support:
PHP 4, PHP 5, PHP 7, PHP 8
Summary: PHP preg_match() Function
preg_match() is a very powerful function as it uses regular expression pattern to find a sub string in a substring. You can also know the position of the substring in the string too. It is one of the Perl Compatible Regular Expressions (PCRE) functions in PHP.