#!/usr/bin/perl
use strict;

permute("1 2 3 4","");

sub permute {
  my $old = @_[0];
  my $new = @_[1];
  my @old = split(/ /,$old);
  my @new = split(/ /,$new);

  print "old = @old | new = @new\n"; #helpful in seeing what's going on

  unless (@old) { print "@new\n"; } else {
    my $i;
    foreach $i (0..$#old) {
      my @new1 = @new;
      my @old1 = @old;
      unshift(@new1,splice(@old1,$i,1));
      my $new1 = join(' ',@new1);
      my $old1 = join(' ',@old1);
      permute($old1,$new1);
    }
  }
}