从 CRON 表达式中获取分钟数 (c#)

Question

I'm trying to find a way how to get a specific value from a CRON expression.

Eg I have this CRON expression "*/5 * * * *" and I need to get minutes. The result must be 5. All I found it's example of usage NCrontab library. It shows how to get schedule:

var schedule = CrontabSchedule.Parse("*/5 * * * *");

Is there any way to solve this problem?

Answer 1

If you simply need the minutes, you shouldn't need the NCrontab library. You can parse this simple enough yourself.

var expression = "*/5 * * * *";
var split = expression.Split(" ".ToCharArray(), StringSplitOptions.RemoveEmptyEntries);

if (split.Length < 5)
    throw new Exception("Invalid CRON expression");

var onlyDigits = "0123456789";

// strip non numeric chars
var minutes = new string(split[0].Where(c => onlyDigits.Contains(c)).ToArray());

Answer 2

I use regular expressions. Try this:

internal static Match GetExpressionRegex(string expression)
        => Regex.Match(
            expression,
            "(?<Minutes>[0-9*,/-]+) (?<Hours>[0-9*,/-]+) (?<Days>[0-9*,/-]+) (?<Month>[0-9*,/\\-a-z]+) (?<DayOfWeek>[0-9*,/\\-a-z]+)",
            RegexOptions.Singleline,
            TimeSpan.FromSeconds(0.2)
        );

Code Reference: https://github.com/rashadrivera/CronExpression/blob/master/CronExpression/Internals/CronExpressionHelper.cs