Super User is a question and answer site for computer enthusiasts and power users. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I need to take two text files and check to see if a line that exists in File A doesn't exist anywhere in File B.

Each line in File A that does not exist in File B should be copied to an output log.

A friend of mine suggested SED but I've never used it before, so how would I go about doing this?

share|improve this question

It sounds like the lines are intended to be unique and order doesn't matter, so try this:

sort fileA > fileA.sort
sort fileB > fileB.sort
diff fileA.sort fileB.sort | sed -n "/^</{s/< //;p}"
share|improve this answer

Lines that only exist in fileA:

comm -23 <(sort fileA) <(sort fileB) > output.txt

All lines unique to fileA will be saved in the file output.txt.

share|improve this answer
Process substitution using the <(...) notation is an elegant solution. I thought about suggesting that form myself but it's only in bash, not the other shells, and it wasn't clear what shell the OP was using. – Nicole Hamilton Dec 2 '12 at 18:40

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .