I have a tool that generates tests and predicts the output. The idea is that if I have a failure I can compare the prediction to the actual output and see where they diverged. The problem is the actual output contains some lines twice, which confuses `diff`. I want to remove the duplicates, so that I can compare them easily. Basically, something like `sort -u` but without the sorting.

Is there any unix command line tool that can do this?