Something to consider, how many people do I want to use my software? If you are writing a program that will be used by lots of people from a variety companies, locations then it is hard to be consultant for that sort of software. Better to either give it away, or use some sort of encryption to hide the source (for example Acme::Clean).

Your other option is that you intend to sell your software to a few large clients. Generally you sell the software for large sums of money and you can protect your code with licensing agreements. That will keep the code from being installed on every Tom, Dick and Harry's business, but I don't think it will keep your customer from installing it a few times on their site. The other advantage of this arrangement is that customers are more likely to use you in a consulting gig, so that is another potential place for income.

As for the question, 'Can you profit?' The Answer is yes, the question how can you profit becomes a bigger question. Finding a solution to a problem is one thing, it is another to convince people that your solution would solve their problem.