Combining results

Say I had two lists of the same hashes and some were removed on the second list due to being cracked is there a program that can join the lists so that both hashes would ouput like so :

65XXf9823a0XXXXab7c7e7XXXX04c3d4:65XXf9823a0XXXXab7c7e7XXXX04c3d4

or just notice there are duplicates in each file and output them on the same line.