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

Answer 1

Thanks to Jordi Salvat i Alabart who posted great solution.

I have only modified existing solution posted by Jordi Salvat i Alabart. It worked for me well, but I wanted to extract particular parts by capturing groups. I have added non-capturing parentheses to be able to extract particular parts of crontab record. It is easy to see which capture group to use when you test output regex at: http://www.regexplanet.com/advanced/java/index.html

Salir.com.
 */

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' => '[0-6]'
    );

    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_re\s+" .
            "|($replacements)\s+" .
            ')' .
            '([^\\s]+)\\s+' .
            '(.*)$';
}

This code generates regex:

^\s*($|#|\w+\s*=|(\*(?:\/\d+)?|(?:[0-5]?\d)(?:-(?:[0-5]?\d)(?:\/\d+)?)?(?:,(?:[0-5]?\d)(?:-(?:[0-5]?\d)(?:\/\d+)?)?)*)\s+(\*(?:\/\d+)?|(?:[01]?\d|2[0-3])(?:-(?:[01]?\d|2[0-3])(?:\/\d+)?)?(?:,(?:[01]?\d|2[0-3])(?:-(?:[01]?\d|2[0-3])(?:\/\d+)?)?)*)\s+(\*(?:\/\d+)?|(?:0?[1-9]|[12]\d|3[01])(?:-(?:0?[1-9]|[12]\d|3[01])(?:\/\d+)?)?(?:,(?:0?[1-9]|[12]\d|3[01])(?:-(?:0?[1-9]|[12]\d|3[01])(?:\/\d+)?)?)*)\s+(\*(?:\/\d+)?|(?:[1-9]|1[012])(?:-(?:[1-9]|1[012])(?:\/\d+)?)?(?:,(?:[1-9]|1[012])(?:-(?:[1-9]|1[012])(?:\/\d+)?)?)*|jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\s+(\*(?:\/\d+)?|(?:[0-6])(?:-(?:[0-6])(?:\/\d+)?)?(?:,(?:[0-6])(?:-(?:[0-6])(?:\/\d+)?)?)*|mon|tue|wed|thu|fri|sat|sun)\s+|(@reboot|@yearly|@annually|@monthly|@weekly|@daily|@midnight|@hourly)\s+)([^\s]+)\s+(.*)$

Or Java alternative to generate this regex (without @X stuff):

public static String buildRegex(){
    // numbers intervals and regex
    Map numbers = new HashMap();
    numbers.put("min", "[0-5]?\\d");
    numbers.put("hour", "[01]?\\d|2[0-3]");
    numbers.put("day", "0?[1-9]|[12]\\d|3[01]");
    numbers.put("month", "[1-9]|1[012]");
    numbers.put("dow", "[0-6]");

    Map field_re = new HashMap();

    // expand regex to contain different time specifiers
    for(String field : numbers.keySet()){
        String number = numbers.get(field);
        String range = "(?:"+number+")(?:-(?:"+number+")(?:\\/\\d+)?)?";
        field_re.put(field, "\\*(?:\\/\\d+)?|"+range+"(?:,"+range+")*");
    }

    // add string specifiers
    String monthRE = field_re.get("month");
    monthRE = monthRE + "|jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec";
    field_re.put("month", monthRE);

    String dowRE = field_re.get("dow");
    dowRE = dowRE + "|mon|tue|wed|thu|fri|sat|sun";
    field_re.put("dow", dowRE);

    StringBuilder fieldsReSB = new StringBuilder();
    fieldsReSB.append("^\\s*(")
            .append("$")
            .append("|#")
            .append("|\\w+\\s*=")
            .append("|");        
            .append("(")
            .append(field_re.get("min")).append(")\\s+(")
            .append(field_re.get("hour")).append(")\\s+(")
            .append(field_re.get("day")).append(")\\s+(")
            .append(field_re.get("month")).append(")\\s+(")
            .append(field_re.get("dow"))
            .append(")")
            .append("\\s+)")
            .append("([^\\s]+)\\s+")
            .append("(.*)$");

    return fieldsReSB.toString();
}