How can I check in a Bash script if my local Git repository has changes?

There are some scripts that do not work correctly if they check for changes.

I tried it like this:

VN=$(git describe --abbrev=7 HEAD 2>/dev/null)

git update-index -q --refresh
CHANGED=$(git diff-index --name-only HEAD --)
if [ ! -z $CHANGED ];
    then VN="$VN-mod"
fi

Is there some kind of boolean check if there has been changes since the last commit, or how can I really test if there are new changes to my local repository?

I’m doing all this for a version creation script (that I found somewhere here).