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Comment by nunoferreira | Hacker News Reader

What about "comm" - compare two sorted files line by line. You can easily get occurrences only in file 1, in both files, only in file 2.

Super powerful and saved me hours of work.

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comm is a really useful tool, with one big caveat — you must make sure your input files are all sorted the exact same way. If not, you can get unexpected results, and worse, might not even realize it.

This may seem obvious, but there are many tiny ways that sorts can differ between locales, operating systems and programs (e.g. Excel), especially when dealing with Unicode. It may look the same 99% of the time, and you may not realize until later that you’ve accidentally filtered out values.

Absolutely! From my experience I only use with listings from the same source with the same sort tool (mostly unix sort).

My advice is to sort the files just-in-time using the shell:

    comm <(sort fileA.txt) <(sort fileB.txt)

GNU comm prints a warning if either file is not sorted, unless all input lines are pairable.

Comm is perfect for scripting usage but you might find diff better for human usage. Added bonus diff also does binary.

Plus diff was in part written by the author of the linked content :).