http://qs321.pair.com?node_id=371015

Ananda has asked for the wisdom of the Perl Monks concerning the following question:

Hello Monks,

I am trying to achieve date validation in a single regex without any additional test conditions. The validations include:

a)Check date format
b)Check for leap
c)Check for the correct number of days in a month

I have followed various examples but have not acheived the desired result.

Thanks in advance for all the help extended.

Ananda

Replies are listed 'Best First'.
Re: Date Validation using just a regex
by Sidhekin (Priest) on Jul 01, 2004 at 09:16 UTC

    Why on earth ... ? Well, why not ... 

    /(?=\d{4}-\d\d-\d\d)             # Date format
 (?=.{8}(?:0[1-9]|[12]\d|3[01])) # Day 01-31
 (?=.{5}(?:0[1-9]|1[0-2]))       # Month 01-12
 (?!.{5}(?:0[2469]|11)-31)       # Not 31 days in those months
 (?!.{5}02-30)                   # Never 30 days in Feb
 (?!...[13579]-02-29)            # Not a leap year
 (?!..[13579][048]-02-29)        # -"-
 (?!..[02468][26]-02-29)         # -"-
 (?!.[13579]00-02-29)            # -"-
 (?![13579][048]00-02-29)        # -"-
 (?![02468][26]00-02-29)         # -"-
/x

    [download]

    print "Just another Perl ${\(trickster and hacker)},"
    The Sidhekin proves Sidhe did it!

[reply]
[d/l]
[select]
      Consider forwarding this node off to Abigail-II for inclusion in Regexp::Common! I'm sure that he'll request that you make it more generic, but I also know that "dates" is on the "to do list" for the module... Zak


      ----
      Zak - the office
[reply]
Re: Date Validation using just a regex
by beable (Friar) on Jul 01, 2004 at 09:08 UTC
    Ananda, I think you have set yourself an impossible task. For example, some countries write dates with the month first, some with the day first, and some with the year first. If a date was "01/02/03", how could you possibly work out what it means? Secondly, why try to do this in a regex, when there are modules which can do it? CPAN time modules CPAN date modules
[reply]

      Difficult yes, unwise perhaps, but not impossible.

      If presented with 01/02/03, with absolutely no context, then you would be correct, but that is rarely the case. All it takes is a few heuristics to be able to make sense of that date.

[reply]
[d/l]
Re: Date Validation using just a regex
by delirium (Chaplain) on Jul 01, 2004 at 15:52 UTC
    If you don't mind an expression regex...

    while(<>){
    chomp;

    $_ = 'Use YYYY-MM-DD format' unless s/^(\d{4})-(\d\d)-(\d\d)$/
    $1<1 || $2<1 || $3<1 ? 'Year, month, and day must be greater than 
+0' :
    $2>12 ? 'Month must be less than 13' :
    $3>31 ? 'Day must be less than 32' :
    $3==30&&$2==2 ? 'February has less than 30 days' :
    $3==29 && $2==2 && $1%4!=0 ? 'February only has 29 days in a leap 
+year' :
    $3==31 && $2 =~ m!0[2469]|11! ? '30 days hath September, yada yada
+..' : $_ /e;

    print ": $_ :\n";
}

    [download]
[reply]
[d/l]

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