Pattern matching in PHP

PHP does pattern matching mainly with regular expressions, using the PCRE (preg_*) functions. A pattern is written between delimiters, e.g. /pattern/flags.

Main functions

Function	Purpose
preg_match($p,$s, $m)` | Finds the first match; returns 1/0 and fills `$m
preg_match_all($p,$s, $m)	Finds all matches
preg_replace($p,$r, $s)	Replaces matches
preg_split($p,$s)	Splits a string on a pattern
preg_grep($p,$arr)	Filters array elements that match

Common syntax

• . any character, \d digit, \w word character, \s whitespace
• ^ start, $ end
• * 0+, + 1+, ? 0 or 1, {n,m} range
• [abc] character class, (a|b) alternation, ( ) capture group
• Flags: i case-insensitive, m multiline

Examples

<?php
// 1. Simple match
if (preg_match("/web/i", "Web Technology")) {
    echo "Found";
}

// 2. Validate an email
$email = "user@example.com";
if (preg_match("/^[\w.+-]+@[\w-]+\.[a-z]{2,}$/i",$email)) {
    echo "Valid email";
}

// 3. Extract digits with a capture group
preg_match("/(\d{3})-(\d{4})/", "Call 555-1234", $m);
echo $m[1] .$m[2];        // 5551234

// 4. Replace
echo preg_replace("/\s+/", " ", "too    many   spaces");   // too many spaces

// 5. Find all numbers
preg_match_all("/\d+/", "a1 b22 c333", $all);
print_r($all[0]);          // 1, 22, 333
?>

Simple (non-regex) matching

For plain text, use strpos(), str_contains(), str_starts_with(), and strcmp(). Use fnmatch() for shell-style wildcards.

Use preg_* for flexible patterns and the simple functions when a fixed substring is enough (they are faster).