#!/usr/bin/perl -l

use strict;
use warnings;

{
    my %df = (
        '99/99/99'   => [qw|DD / MM / RR|],
        '99/99/9999' => [qw|DD / MM / YYYY|],
        '9999/99/99' => [qw|YYYY / MM / DD|],
    );

    sub dateformat {
        my @in=split /(9+)/, shift;
        shift @in;
        my @out=@{ $df{join '/', @in[0,2,4]} };
        @out[1,3]=@in[1,3];
        join '', @out;
    }
}

chomp, print dateformat $_ while <DATA>;

__END__
99-99/99
99.99.9999
9999.99-99