C# expression to validate a Cron job

Whats the best way to validate something like this expression is a valid cron expression, (in C#)

“At 00:00 on Friday.”
Cron Expression passed in
0 0 * * FRI

>Solution :

You can use this: https://www.nuget.org/packages/NCrontab.Advanced/

or using this reference:

https://quartznet.sourceforge.io/apidoc/2.0/html/

bool IsValid = IsValidSchedule("0 0 * * FRI"); 

Then:

   public static bool IsValidSchedule(string schedule) {
    
            var valid = CronExpression.IsValidExpression(schedule);
            // Some expressions are parsed as valid by the above method but they are not valid, like "* * * ? * *&54".
            //In order to avoid such invalid expressions an additional check is required, that is done using the below regex.
    
            var regex = @"^\s*($|#|\w+\s*=|(\?|\*|(?:[0-5]?\d)(?:(?:-|\/|\,)(?:[0-5]?\d))?(?:,(?:[0-5]?\d)(?:(?:-|\/|\,)(?:[0-5]?\d))?)*)\s+(\?|\*|(?:[0-5]?\d)(?:(?:-|\/|\,)(?:[0-5]?\d))?(?:,(?:[0-5]?\d)(?:(?:-|\/|\,)(?:[0-5]?\d))?)*)\s+(\?|\*|(?:[01]?\d|2[0-3])(?:(?:-|\/|\,)(?:[01]?\d|2[0-3]))?(?:,(?:[01]?\d|2[0-3])(?:(?:-|\/|\,)(?:[01]?\d|2[0-3]))?)*)\s+(\?|\*|(?:0?[1-9]|[12]\d|3[01])(?:(?:-|\/|\,)(?:0?[1-9]|[12]\d|3[01]))?(?:,(?:0?[1-9]|[12]\d|3[01])(?:(?:-|\/|\,)(?:0?[1-9]|[12]\d|3[01]))?)*)\s+(\?|\*|(?:[1-9]|1[012])(?:(?:-|\/|\,)(?:[1-9]|1[012]))?(?:L|W)?(?:,(?:[1-9]|1[012])(?:(?:-|\/|\,)(?:[1-9]|1[012]))?(?:L|W)?)*|\?|\*|(?:JAN|FEB|MAR|APR|MAY|JUN|JUL|AUG|SEP|OCT|NOV|DEC)(?:(?:-)(?:JAN|FEB|MAR|APR|MAY|JUN|JUL|AUG|SEP|OCT|NOV|DEC))?(?:,(?:JAN|FEB|MAR|APR|MAY|JUN|JUL|AUG|SEP|OCT|NOV|DEC)(?:(?:-)(?:JAN|FEB|MAR|APR|MAY|JUN|JUL|AUG|SEP|OCT|NOV|DEC))?)*)\s+(\?|\*|(?:[0-6])(?:(?:-|\/|\,|#)(?:[0-6]))?(?:L)?(?:,(?:[0-6])(?:(?:-|\/|\,|#)(?:[0-6]))?(?:L)?)*|\?|\*|(?:MON|TUE|WED|THU|FRI|SAT|SUN)(?:(?:-)(?:MON|TUE|WED|THU|FRI|SAT|SUN))?(?:,(?:MON|TUE|WED|THU|FRI|SAT|SUN)(?:(?:-)(?:MON|TUE|WED|THU|FRI|SAT|SUN))?)*)(|\s)+(\?|\*|(?:|\d{4})(?:(?:-|\/|\,)(?:|\d{4}))?(?:,(?:|\d{4})(?:(?:-|\/|\,)(?:|\d{4}))?)*))$";
    
            return valid&& Regex.IsMatch(schedule, regex);
        }