Comparing two files in linux terminal

if you have vim installed,try this:

vimdiff file1 file2

or

vim -d file1 file2

you will find it fantastic.

Sort them and use comm:

comm -23 <(sort a.txt) <(sort b.txt)

comm compares (sorted) input files and by default outputs three columns: lines that are unique to a, lines that are unique to b, and lines that are present in both. By specifying -1, -2 and/or -3 you can suppress the corresponding output. Therefore comm -23 a b lists only the entries that are unique to a. I use the <(...) syntax to sort the files on the fly, if they are already sorted you don't need this.

If you prefer the diff output style from git diff, you can use it with the --no-index flag to compare files not in a git repository:

git diff --no-index a.txt b.txt

Using a couple of files with around 200k file name strings in each, I benchmarked (with the built-in timecommand) this approach vs some of the other answers here:

git diff --no-index a.txt b.txt# ~1.2scomm -23 <(sort a.txt) <(sort b.txt)# ~0.2sdiff a.txt b.txt# ~2.6ssdiff a.txt b.txt# ~2.7svimdiff a.txt b.txt# ~3.2s

comm seems to be the fastest by far, while git diff --no-index appears to be the fastest approach for diff-style output.

Update 2018-03-25 You can actually omit the --no-index flag unless you are inside a git repository and want to compare untracked files within that repository. From the man pages:

This form is to compare the given two paths on the filesystem. You can omit the --no-index option when running the command in a working tree controlled by Git and at least one of the paths points outside the working tree, or when running the command outside a working tree controlled by Git.