perl -le "@a = sort{ print qq($a $b); 0 }@ARGV" 1 2 3 4
1 2
3 4
1 3
3 2

perl -le "@a = sort{ print qq($a $b); 1 }@ARGV" 1 2 3 4
1 2
3 4
2 4
2 3

perl -le "@a = sort{ print qq($a $b); -1 }@ARGV" 1 2 3 4
1 2
3 4
1 3
3 2
2 4                                                      # one iteration more with -1