Cron Day-of-Month Field Regex for PHP

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching cron day-of-month field, ported and verified for PHP. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your PHP project — whether you're validating in a Laravel validator, a WordPress plugin, or a standalone PHP script.

Php Implementation

<?php
// Cron Day-of-Month Field
// ReDoS-checked | RegexVault — Dev & Systems > Cron

define('CRON_DAYOFMONTH_FIELD_PATTERN', '/^(?:[?]|\*(?:\/[1-9]|\/[12][0-9]|\/3[01])?|(?:[1-9]|[12][0-9]|3[01])(?:-(?:[1-9]|[12][0-9]|3[01]))?(?:\/[1-9]|\/[12][0-9]|\/3[01])?(?:,(?:[1-9]|[12][0-9]|3[01]))*)$/');

function validate_cron_dayofmonth_field(string $input): bool {
    return (bool) preg_match(CRON_DAYOFMONTH_FIELD_PATTERN, $input);
}

// Example
var_dump(validate_cron_dayofmonth_field("*")); // bool(true)

Test Cases

When to use this pattern

This pattern is drawn from the Dev & Systems > Cron category and has been checked for ReDoS risk. That matters for PHP developers because especially relevant in PHP where PCRE backtracking limits can trigger silent failures on malicious input. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

? is used in Quartz scheduler and AWS EventBridge to indicate no specific value. Standard Unix cron does not support ?. Day 31 is structurally valid but semantically invalid for short months.