Diff-ing files with Linux command

Question

What Linux command allow me to check if all the lines in file A exist in file B? (it's almost like a diff, but not quite). Also file A has uniq lines, as is the case with file B as well.

Answer 1

The comm command compares two sorted files, line by line, and is part of GNU coreutils.

Answer 2

Are you looking for a better diff tool?

https://stackoverflow.com/questions/12625/best-diff-tool