How to Use preg_match in PHP: Syntax and Examples

Use preg_match in PHP to check if a string matches a pattern defined by a regular expression. It returns 1 if the pattern matches, 0 if not, and false on error. The basic syntax is preg_match('/pattern/', $string, $matches) where $matches stores the found results.

Syntax

The preg_match function checks if a string matches a regular expression pattern.

• pattern: The regular expression enclosed in delimiters, usually slashes /pattern/.
• subject: The string you want to test.
• matches (optional): An array to store the matched parts.
• flags and offset (optional): Advanced options for matching behavior.

php

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

Example

This example checks if the string contains the word "cat" and prints the matched word.

php

<?php
$pattern = '/cat/';
$text = 'The cat is sleeping.';
if (preg_match($pattern, $text, $matches)) {
    echo "Match found: " . $matches[0];
} else {
    echo "No match found.";
}
?>

Output

Match found: cat

Common Pitfalls

Common mistakes when using preg_match include:

• Forgetting delimiters around the pattern (e.g., using cat instead of /cat/).
• Not escaping special characters in the pattern.
• Assuming preg_match returns the matched string instead of 1 or 0.
• Not checking the return value before using the $matches array.

php

<?php
// Wrong: missing delimiters
// preg_match('cat', 'cat', $matches); // This causes a warning

// Right: with delimiters
preg_match('/cat/', 'cat', $matches);
echo $matches[0]; // Outputs: cat
?>

Output

cat

Quick Reference

Usage	Description
preg_match('/pattern/', $string)	Returns 1 if pattern matches, 0 if not
preg_match('/pattern/', $string, $matches)	Stores matched parts in $matches array
Use delimiters like / or #	Required around the regex pattern
Escape special chars with \\	To match characters like . * + ? etc.
Check return value before using $matches	Avoid errors if no match found

Key Takeaways

Always enclose your regex pattern in delimiters like slashes (/pattern/).

preg_match returns 1 if a match is found, 0 if not, and false on error.

Use the optional $matches array to get the matched text from the string.

Escape special regex characters to match them literally.

Check the return value before accessing $matches to avoid errors.