use Algorithm::Combinatorics qw[ permutations ];

my $iter = permutations( [ reverse 0 .. 9 ] );

print join '', @$_ while defined( $_ = $iter->next );
9876543210
9876543201
9876543120
9876543102
9876543021
9876543012
9876542310
9876542301
9876542130
9876542103
9876542031
9876542013
9876541320
...