Comparing two files in linux terminal

Question

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
# ~1.2s

comm -23 <(sort a.txt) <(sort b.txt)
# ~0.2s

diff a.txt b.txt
# ~2.6s

sdiff a.txt b.txt
# ~2.7s

vimdiff 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.

Try sdiff (man sdiff)

sdiff -s file1 file2

You can use diff tool in linux to compare two files. You can use --changed-group-format and --unchanged-group-format options to filter required data.

Following three options can use to select the relevant group for each option:

• '%<' get lines from FILE1

• '%>' get lines from FILE2

• '' (empty string) for removing lines from both files.

E.g: diff --changed-group-format="%<" --unchanged-group-format="" file1.txt file2.txt

[root@vmoracle11 tmp]# cat file1.txt 
test one
test two
test three
test four
test eight
[root@vmoracle11 tmp]# cat file2.txt 
test one
test three
test nine
[root@vmoracle11 tmp]# diff --changed-group-format='%<' --unchanged-group-format='' file1.txt file2.txt 
test two
test four
test eight

You can also use: colordiff: Displays the output of diff with colors.

About vimdiff: It allows you to compare files via SSH, for example :

vimdiff /var/log/secure scp://192.168.1.25/var/log/secure

Extracted from: http://www.sysadmit.com/2016/05/linux-diferencias-entre-dos-archivos.html