A regular expression only works character by character, not token by token. So, if you want to match a two-digit number, you have to specify two characters that can match 0 through 9.

Your expression  [0-59\*] will allow the characters 0,1,2,3,4,5,9 and *, which, likely, isn't what you wanted. To match a digit between 0 and 59, or a *, you could use the following regular expression:

  ([012345]?\d|\*)

[download]

That is, you allow the first digit (if any) to be between 0 and 5, and then require a second digit after it, you just don't care what it is.

For matching digits between 0 and 23, it gets trickier:

  ([01]?\d|2[0123]|\*)

[download]

The approach is to match (optionally) a zero or one, and then any digit. If the first digit is a 2, we explicitly require a 0, 1, 2 or 3.

Is there any reason you're forced to parsing the crontab yourself? There is Schedule::Cron and some other Crontab parsers, and your regular expression does not cover the weirder (Vixie) cron extensions like */3, which allows to trigger an event every 3 units, or 1,5,7,9,11, which would trigger the event at 1 minute, 5 minutes, 7 minutes and so on.

Update: ikegami pointed out that I forgot to allow for *.

In reply to Re: simple pattern match ? by Corion
in thread simple pattern match ? by Anonymous Monk

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