man diff does not correspond to the diff version installed

Question

executing man diff tells the following:

NAME
       diff - compare files line by line

SYNOPSIS
       diff [OPTION]... FILES

DESCRIPTION
       Compare files line by line.

       -i  --ignore-case
              Ignore case differences in file contents.

[...]
       -q  --brief
              Output only whether files differ.
[...]

but when I use the -q option, it fails with fatal: invalid diff option/value: -q

Why does the man of the diff command do not correspond to the version installed?

How to fix it?

Is there a brew package who has a version of the diff command with the -q option? (brew coreutils and binutils do not have the diff command)

OSX 10.11.5

Update with your questions

$ which diff
/usr/bin/diff

$ diff --version
usage: git diff --no-index <path> <path>

$ diff -v
usage: git diff --no-index <path> <path>

$ command diff --version
diff (GNU diffutils) 2.8.1

I use brew and https://github.com/donnemartin/dev-setup

If I disable the .bash_profile installed by dev-setup, then which diff still returns the same path but diff -q works.

Answer 1

Do you, by any chance, use anything like pretzo or something similar? Some frameworks like this will (badly) define their own functions replacing the terminal default ones.

In that case, try running command diff -q ... and see if this resolves the issue.

Edit: As @MarkPlotnick pointed out, dev-setup is another framework that overrides the default diff command and uses git diff instead:

# Use Git’s colored diff when available
hash git &>/dev/null;
if [ $? -eq 0 ]; then
    function diff() {
        git diff --no-index --color-words "$@";
    }
fi;

Reference: https://github.com/donnemartin/dev-setup/blob/master/.functions