#!/usr/bin/perl -w
# filename: combo
use strict;

my $entry = shift;

my @array =
    $entry =~ m/^(\d)(\d)(\d)$/ ?
    ($1.$2.$3, $1.$3.$2, $2.$1.$3, $2.$3.$1, $3.$1.$2, $3.$2.$1) :
    ();

@array or die "Bad input: ${entry}\n";

@array = do {
    my %hash;
    @hash{@array} = ();
    keys %hash;
};

print "${entry} was entered.",
    " The different combinations would be @{array}.\n";

__END__
$ perl combo 123
123 was entered. The different combinations would be 231 123 312 321 213 132.
$ perl combo 122
122 was entered. The different combinations would be 221 212 122.