I agree that the requirements seem slightly misguided, but here is an attempt anyway. The approach is to make two subs, one that validates a year, month and date, and one that splits a number into all possible year,month and date combos and to pass to the first.

Its late, I'm tired, so this could definitely be improved, but its a start. 

#!/usr/bin/perl -w

use strict;

=pod

yyyymmdd
yyyyddmm
ddmmyyyy
mmddyyyy
yymmdd
yyddmm
ddmmyy
mmddyy

=cut

my %months = (
  1=>31, 2=>28, 3=>31, 4=>30, 5=>31, 6=>30,
  7=>31, 8=>31, 9=>31, 10=>31, 11=>30, 12=>31 ); 

for (<DATA> ) {
  chomp;
  print "$_ ";  
  print validate( $_ ) ? 'yep' : 'nope';
  print "\n";
}

sub validate_ymd {
  my ($y,$m,$d) = @_;

  # last minute addition / hack to make year 4 digit
  if ( length( $y ) == 2 ) {
    if ( $y > 3 ) {
      $y += 1900;
    } else {
      # close readers will see that these are equivalent...
      return 1 if validate_ymd( 1900 + $y, $m, $d ); 
      return 1 if validate_ymd( 2000 + $y, $m, $d );
      return 0;
    } 
  } 

  $y = int($y); $m=int($m); $d=int($d);

  return 0 if $y > 2003;
  return 0 if $y < 1900;

  my $leap = 0;
  if ( $m == 2 and !$y or !($y % 4) ) {
    $leap = 1;
  }

  return 0 unless exists $months{$m};
  return 0 unless $d and $d <= $months{$m} + $leap;
  print " (y $y m $m d $d) ";
  return 1;
}

sub validate {
  my $date = shift;
  return 0 if $date =~ /\D/; 

  my $length = length( $date );
  return 0 unless $length == 6 or $length == 8; 

  my @attempts;
  if ( $length == 6 ) {
    $date =~ /(..)(..)(..)/; 
    push @attempts, [$1,$2,$3], [$1,$3,$2], [$3,$1,$2], [$3,$2,$1];  

  } elsif ( $length == 8 ) {
    $date =~ /(....)(..)(..)/;
    push @attempts, [$1,$2,$3], [$1,$3,$2];  
    $date =~ /(..)(..)(....)/;
    push @attempts, [$3,$1,$2], [$3,$2,$1];  
  }
  foreach ( @attempts ) {
    return 1 if validate_ymd( @$_ );
  }
  return 0;
}

__DATA__
20000229
19970229
29020300
291254
002902
19990223
101172

[download]

gives: 

20000229  (y 2000 m 2 d 29) yep
19970229 nope
29020300 nope
291254  (y 1954 m 12 d 29) yep
002902  (y 1900 m 2 d 29) yep
19990223  (y 1999 m 2 d 23) yep
101172  (y 1972 m 10 d 11) yep

[download]

In reply to Re: Numeric Date Validation by qq
in thread Numeric Date Validation by booter

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