my %dateformat = (
  '99(.)99(.)99' => '"DD${1}MM${2}RR"',
  '99(.)99(.)9999' => '"DD${1}MM${2}YYYY"',
  '9999(.)99(.)99' => '"YYYY${1}MM${2}DD"',
);
DATE: while (<DATA>) {    ## updated: it was 'foreach'
    chomp;
    foreach my $k (keys %dateformat) {
        next unless /^$k$/;
        my $trans = $_;
        $trans =~ s/^$k$/$dateformat{$k}/ee;
        print "translated <$_> to <$trans>\n";
        next DATE;
    }
    warn "$_ unmatched\n";
}
__DATA__
99/99/9999
99/99/99
99-99-9999
9999999
9999@99#99