./combinations.pl a b

output:
a,a
a,b
b,a
b,b

##</code><code>##

#!/usr/bin/perl
#################################################################################
#FILE                : combinations.pl
#USAGE                           :  ./combinations.pl arguments
#                                               eg,
#                                                       ./combinations.pl a b
#                                                       output:
#                                                       a,a
#                                                       a,b
#                                                       b,a
#                                                       b,b
#DESCRIPTION         : This program will give possible combinations or elements
#                                               in a set,
#                                               eg,
#                                               if a,b is the input(argument ot the program
#                                               the output is
#                                               a,a
#                                               a,b
#                                               b,a
#                                               b,b
#                                               the idea to create this program is, when I wanted my program
#                                               to work for multiple configurations like a,b etc
#                                               then I have to look out for atleast four combinations.
#AUTHOR              : Targetsmart
#CREATED DATE        : 17/12/2008 17:12:58 IST
#       ( NOTE : Date format is DD/MM/YYYY HH:MM:SS  )
##################################################################################
use strict;
use warnings;
use diagnostics;
use Data::Dumper;
use Clone qw(clone); # for deep copy of data structures

our (@Buf,$Possibilities);
if(@ARGV){
&process(&populatedata(@ARGV));
}else{
        #my @actualdata= qw(connection no-connection);
        my @actualdata= qw(a b);
        #my @actualdata= (0..6);
        &process(&populatedata(@actualdata));
}

################################################################################
# just a replication of actual array into number of arrays of same content
# the number of arrays depends on the size of the array
# eg,
# a,b is actual array
# this function will prepare
# [a,b], [a,b]

# a,b,c is actual array
# this function will prepare
# [a,b,c], [a,b,c], [a,b,c]

sub populatedata {
        my (@mainResult);
        push (@mainResult , [@_]) for 0..$#_;
        return \@mainResult;
}
################################################################################

################################################################################
# this recursive function which is take the replicated array like
# [a,b,c], [a,b,c], [a,b,c]
#  and produce the possible combinations.
# like
# a,a,a
# a,a,b
# a,a,c
# a,b,a
# ....
sub process()
{
        my($Data) = shift;
        my $MyArray =  shift @{$Data};
#print Dumper  $MyArray;
        foreach my $Index (@{$MyArray})
        {
                push(@Buf,$Index);
# checking the next array if exists
                if(exists $Data->[0]){
# if there is a next array then supply the data
# by doing a clone to retain the actual $data for
# recursion, if not cloned then the actual data
# reference will not be retained
# eg,
# consider the array or arrays
# [a,b],[a,b] exist
# when cloned
# a,a
# a,b  after printing this
# recursion will return
# but the $Data is already emptied out not available for printing 'b' combination
# b,a
# b,b
# BUT if we clone
# a,a
# a,b  after printing this
# recursion will return
# but the $Data is will contain [a,b] and available for printing 'b' combination
# b,a
# b,b
                        &process(clone($Data));
                        pop(@Buf);
                }else{
                        $"=",";
# counting the combination sequence number.
                        $Possibilities++;
                        print "$Possibilities,@Buf\n";
                        pop @Buf;
                }
        }
}

################################################################################