regex - Validating Crontab Entries with PHP

Question

What is the best way to validate a crontab entry with PHP? Should I be using a regex, or an external library? I've got a PHP script that adds/removes entries from a crontab file, but want to have some way to verify that the time interval portion is in a valid format.

Answer 1

Who said regular expressions can't do that?

Courtesy of my employer, Salir.com, here's a PHPUnit test which does such validation. Feel free to modify & distribute. I'll appreciate if you keep the @author notice & link to web site.

<?php
/**
 * @author Jordi Salvat i Alabart - with thanks to <a href="www.salir.com">Salir.com</a>.
 */

abstract class CrontabChecker extends PHPUnit_Framework_TestCase {
    protected function assertFileIsValidUserCrontab($file) {
        $f= @fopen($file, 'r', 1);
        $this->assertTrue($f !== false, 'Crontab file must exist');
        while (($line= fgets($f)) !== false) {
            $this->assertLineIsValid($line);
        }
    }

    protected function assertLineIsValid($line) {
        $regexp= $this->buildRegexp();
        $this->assertTrue(preg_match("/$regexp/", $line) !== 0);
    }

    private function buildRegexp() {
        $numbers= array(
            'min'=>'[0-5]?d',
            'hour'=>'[01]?d|2[0-3]',
            'day'=>'0?[1-9]|[12]d|3[01]',
            'month'=>'[1-9]|1[012]',
            'dow'=>'[0-7]'
        );

        foreach($numbers as $field=>$number) {
            $range= "($number)(-($number)(/d+)?)?";
            $field_re[$field]= "*(/d+)?|$range(,$range)*";
        }

        $field_re['month'].='|jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec';
        $field_re['dow'].='|mon|tue|wed|thu|fri|sat|sun';

        $fields_re= '('.join(')s+(', $field_re).')';

        $replacements= '@reboot|@yearly|@annually|@monthly|@weekly|@daily|@midnight|@hourly';

        return '^s*('.
                '$'.
                '|#'.
                '|w+s*='.
                "|$fields_res+S".
                "|($replacements)s+S".
            ')';
    }
}