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";
}
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