Shell Programming and Scripting

20120426

20122604

/^20\d\d(0[1-9]|1[012])(0[1-9]|[12][0-9]|3[01])$/

 
$ cat one.pl
#!/bin/perl
use Time::Local;
my $date = $ARGV[0];
$date =~ s/\s+$//;
$date =~ s/^\s*//;
my ($year, $month, $day) = unpack "A4 A2 A2", $date;
eval{ 
    timelocal(0,0,0,$day, $month-1, $year); # dies in case of bad date
    print "$date is valid\n";
} or print "Bad date: $@";

bash-3.2$ perl one.pl 20120430
20120430 is valid

bash-3.2$ perl one.pl 20120431
Bad date: Day '31' out of range 1..30 at one.pl line 8

bash-3.2$ perl one.pl 20120231
Bad date: Day '31' out of range 1..29 at one.pl line 8

bash-3.2$ perl one.pl 20120229
20120229 is valid

bash-3.2$ perl one.pl 20120230
Bad date: Day '30' out of range 1..29 at one.pl line 8