PHP preg_match() Function

What does preg_match() do?

preg_match() searches $subject for the first match of a Perl-compatible regular expression (PCRE). It returns 1 if the pattern matches and 0 if not, and fills $matches with the full match ($matches[0]) and any capture groups.

Syntax

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

Parameters

• $pattern - The regex including delimiters, e.g. '/^\d+$/'. Modifiers follow the closing delimiter: i case-insensitive, u UTF-8, m multiline, s dot matches newline.
• $subject - The string to search.
• $matches - Optional. Filled with the full match at index 0, numbered groups at 1, 2 ..., and named groups by name.
• $flags - PREG_OFFSET_CAPTURE (also return positions) or PREG_UNMATCHED_AS_NULL.
• $offset - Byte position to start searching from.

Return value

1 on a match, 0 if there is no match, or false if the pattern is invalid. Compare with === 1 when the difference matters.

preg_match() examples

Every example below shows the exact output it produces. Paste any of them into the editor above (or the online compiler) to run it.

1. Match and capture a number

<?php
$text = "Order #4521 shipped on 2026-03-15";
if (preg_match('/#(\d+)/', $text, $matches)) {
    echo "Full match: " . $matches[0] . "\n";
    echo "Order number: " . $matches[1] . "\n";
}
var_dump(preg_match('/refund/', $text));

Output:

Full match: #4521
Order number: 4521
int(0)

2. Named capture groups

<?php
$date = "2026-03-15";
if (preg_match('/^(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})$/', $date, $m)) {
    echo "Year: {$m['year']}, Month: {$m['month']}, Day: {$m['day']}\n";
}

Output:

Year: 2026, Month: 03, Day: 15

3. Validate input with a regex

<?php
$checks = [
    'username'  => ['/^[a-z0-9_]{3,16}$/', 'john_doe'],
    'zip code'  => ['/^\d{5}(-\d{4})?$/', '12345-678'],
    'hex color' => ['/^#[0-9a-f]{6}$/i', '#1A2b3C'],
];
foreach ($checks as $label => [$pattern, $value]) {
    $ok = preg_match($pattern, $value) === 1;
    echo str_pad($label, 10) . $value . " => " . ($ok ? "valid" : "invalid") . "\n";
}

Output:

username  john_doe => valid
zip code  12345-678 => invalid
hex color #1A2b3C => valid

4. Starts with, ends with, case-insensitive

<?php
$text = "mr.sanket";
echo preg_match('/^mr/', $text) ? "starts with mr\n" : "does not start with mr\n";
echo preg_match('/sanket$/', $text) ? "ends with sanket\n" : "does not end with sanket\n";
echo preg_match('/^MR/i', $text) ? "case-insensitive match\n" : "no match\n";

Output:

starts with mr
ends with sanket
case-insensitive match

5. All matches with preg_match_all()

<?php
$text = "Prices: $4.99, $12.50 and $100";
$count = preg_match_all('/\$(\d+(?:\.\d{2})?)/', $text, $matches);
echo "Found $count prices: " . implode(", ", $matches[1]) . "\n";

Output:

Found 3 prices: 4.99, 12.50, 100

Common mistakes and gotchas

• Delimiters are required: preg_match("\d+", $s) fails with a warning. Write '/\d+/', or '#...#' when the pattern contains slashes.
• Use single quotes for patterns so PHP does not interpret \d or $ inside double-quoted strings.
• User input in patterns: escape it with preg_quote($input, '/').
• Emails and URLs: prefer filter_var($email, FILTER_VALIDATE_EMAIL) over hand-written regexes.
• Only the first match: use preg_match_all() to find every match.