Personally, I would do a simple regular expression to split the date string into year, month and date and then use one of the the popular Date handling modules to do the validation - a regular expression to get the correct days for the months is going to be monstrous if not impossible.

/J\

I think the simple, straight-forward answer is: don't. Use a regular expression to pull apart the data, and do minor syntax checking, and use other date-related modules to do semantic checking.

Here's a solution that uses the core module Time::Local

use Time::Local qw( timegm );

/(\d{4})[-\/.](\d{2})[-\/.](\d{2})/
  or die("Bad format\n");

my $time = eval { timegm(0, 0, 0, $3, $2, $1) };
die("Bad date\n") if $@;
[download]

Switch timegm for timelocal if you prefer.

You're trying to make a regex do the work of a subroutine. The way to do leap day checks requires division checks on the year, but you only need to worry about that if the month February and the day is 29.

Date::Calc (mentioned above) has a check_date() function that can do exactly what you are looking for (provided you split the date into year, month and day first).

use strict;
use warnings;
use Date::Calc qw(check_date);

my $date = "9999/12/11";
my($year,$month,$day) = $date =~ /(\d+)\/(\d+)\/(\d+)/;
print "$year/$month/$day is ";
if(check_date($year,$month,$day) && $year >=1753 && $year <= 9999)
{
    print "valid";
}
else
{
    print "not valid\n";
}
[download]

Chris

That has the added benefit of being easier to understand when you take a look at this code again a month from now.

I'm going to echo don't. To start with, as other's have pointed out RE is the wrong tool for this job and modules such as Date::Calc are there to do it for you. But then threre's the issue of your "simple" regular expression that is broken. I'm surprised no one pointed it out...

((17((5[3-9])|([6-9]\d)))|((18|19)\d\d)|([2-9]\d\d\d))[-/.](0[1-9]|1[0
+12])[- /.](0[1-9]|[12][0-9]|3[01])   
                                                        ^ unescaped / 
+terminates the RE if you use it in /((17...)/
but even if you encapsulate it in a variable there's still problems:

#!/usr/bin/perl

@sampdata = qw (
894/7/14
1752/8/12
1753/12/24
1957/8/30
3998/4/22
9999/3/15
10000/1/1
);

$re = "((17((5[3-9])|([6-9]\d)))|((18|19)\d\d)|([2-9]\d\d\d))[-/.](0[1
+-9]|1[012])[- /.](0[1-9]|
[12][0-9]|3[01])";

while (<@sampdata>) {
        print;
        print ( /$re/ ? " is " : " is not " );
        print " in range 1753 to 9999\n";
}

__END__



894/7/14 is not  in range 1753 to 9999
1752/8/12 is not  in range 1753 to 9999
1753/12/24 is  in range 1753 to 9999
1957/8/30 is not  in range 1753 to 9999
3998/4/22 is not  in range 1753 to 9999
9999/3/15 is not  in range 1753 to 9999
10000/1/1 is not  in range 1753 to 9999

So a change of 
    ((17((5[3-9])|([6-9]\d)))
to 
    ((17((5[3-9])|(1([6-9]\d))))
Seems to be in order.

Re: the two instances of [-/.], was the second one supposed to include
+ a space?
[download]

There's another good resource called the regular expressions library - try this listing for some examples.

There's another good resource called the regular expressions library - try this listing for some examples.

You apparently haven't seen my rant about that place. Nor looked at the number of specific items in the past few months that I've commented on that are broke, misleading, or should be better done without regex.

That place is a joke. Blind leading the blind.

-- Randal L. Schwartz, Perl hacker
Be sure to read my standard disclaimer if this is a reply.

You're right of course - I hadn't come across your blog post about it (and being a bit of a newb, haven't seen your perlmonks posts).

Mixing my metaphores perhaps, but there's more than one way to do it, but some ways are more equal than others :)

#!perl  -w
use strict;

for my $y ( 1753 .. 9999 )
{
for my $m ( 1 .. 12 )
{
for my $d ( 1 .. 31 )
{
my $date = sprintf "%04d/%02d/%02d", $y, $m, $d;

if ( $date !~ 
m/^
########################
# Year 
([2-9]\d{3}|1[89]\d\d|17[6-9]\d|175[3-9])
\/ #####################
# Month
(0[1-9]|1[0-2])
\/ #####################
# Day
(
0[1-9]|1\d|2[0-8]|  # 01 - 28
(?<=(?:0[13578]|10|12)\/)(?:29|3[01])| #  to 31
(?<=(?:0[469]|11)\/)(?:29|30)| #  to 30
(?<=(?:
    (?:2[048]|3[26]|4[048]|5[26]|6[048]|7[26]|8[048]|9[26])00|
    \d\d(?:0[48]|1[26]|2[048]|3[26]|4[048]|5[26]|6[048]|7[26]|8[048]|9
+[26])\/02\/)
    )(?:29) # Leap year
)
########################
$/x 
)
{
print "$date is invalid\n";
}
# Else $1 == year, $2 == month, $3 == day
}}}
[download]

Update: I realized that I made a mistake listing leap-years. I've now fixed that, but it further demonstrates why a module is better.