How you extract the diff from two text files in linux

Q: You have the two files file1.txt and file2.txt. Now what you want to get is the lines in file1, but not in file2, how to do this by command in linux?

A: If your files are sorted already in linux, then there is a command already has this ability to do:

comm

NAME
 comm - compare two sorted files line by line

SYNOPSIS
 comm [OPTION]... FILE1 FILE2

...

-1 suppress lines unique to FILE1

-2 suppress lines unique to FILE2

-3 suppress lines that appear in both files

So this command will solve your issue:

comm -2 -3 file1.txt file2.txt > fileResult.txt

 

But if your file is not sorted, how?

There is another way to solve this too, suppose all your lines are less than 400 chars.

diff -a --width=400 --suppress-common-lines -y file1.txt file2.txt > fileResult.txt

 

By this diff command, the result you get is not clear in fact, as it compensates each line with “…..(spaces)….<“, so you still need to find and search this kind of extras and remove them.

If you get a better way in diff way, please let me know. Thanks here.