I have two files, both with a lot of data, what I need is compare the first word of each file (each file always starts with a number, and each number could have many digits). The files are identical when these numbers are the same. Example: I have 3 files: a.txt, b.txt and c.txt a.txt content is "1 a b c 3 5 6 hjkj" b.txt content is "1 c f a 1234 h" c.txt content is "2 a b c 3 5 6 hjkj" diff a.txt b.txt should return "files are identical" diff a.txt c.txt should return "files are different" How can I compare them using the diff command?