#Sample use:
my @elts= @ARGV;
my $sep= " ";
do {
    if(  ! @ARGV  ) {
        print "What to permute? ";
        my $line= <STDIN>;
        chomp( $line );
        exit 0   if  "" eq $line;
        if(  $line =~ / /  ) {
            $sep= " ";
            @elts= split " ", $line;
        } else {
            $sep= "";
            @elts= split //, $line;
        }
    }
    @elts= sort @elts;
    my $cnt= 0;
    do {
        print ++$cnt, ": ", join( $sep, @elts ), "\n";
    } while( nextpermute(@elts) );
} while(  ! @ARGV  );
exit 0;