perl -le'%h=(), undef @h{split"",$_}, keys %h == 3 and print for "0000".."9999"'

##</code><code>##

#!/usr/bin/perl -lw
use strict;

for ( '0000'..'9999' ) {
    my %h;
    undef @h{split'',$_};
    keys %h == 3 and print;
}