Diff-command: doesn't print lines that are different but still says the two files are different

Question

I'm using the diff command to compare two text files. They need to be literally matched.

So I use the diff:

diff binary.out binary.expected

(By the way, those files are NOT binary files. They are text file. I call them binary because that's the name of the project)

and got

Binary files binary.out and binary.expected differ

When I use another diff tool, the smartest of all (AKA human), and there's really nothing different between the two files.

Does anyone happen to know what's going on here?

Thanks.

Answer 1

diff from diffutils says the following about text/binary:

diff determines whether a file is text or binary by checking the first few bytes in the file; the exact number of bytes is system dependent, but it is typically several thousand. If every byte in that part of the file is non-null, diff considers the file to be text; otherwise it considers the file to be binary.

hence GNU diff have a quite open definition of what is text, and the use of the --text option to force it to treat the file as text should seldom be needed.

Have you checked if binary.out or binary.expected contains null characters? What version is your diff program?