/^(\d)(?!\d*\1)(\d)(?!\d*\2)(\d)(?!\d*\3)\d$/;

##</code><code>##

use warnings;
use strict;
for my $one (0 .. 3) {
    for my $two (0 .. 3) {
        for my $three (0 .. 3) {
            for my $four (0 .. 4) {
                my $test = "$one$two$three$four";
                print "$test\n" if $test=~m/^[0-3]{4}$/ and $test=~m/^(\d)(?!\d*\1)(\d)(?!\d*\2)(\d)(?!\d*\3)\d$/;
            }
        }
    }
}

##</code><code>##

0123
0132
0213
0231
0312
0321
1023
1032
1203
1230
1302
1320
2013
2031
2103
2130
2301
2310
3012
3021
3102
3120
3201
3210