Don't allow git --all when files are currently staged. ~ An interesting lesson in git's use of environment vars (GIT_INDEX_FILE)

pre-commit

# don't allow --all when we have staged files. It's usually a mistake
# depends on procfs and won't work through gitaliases
while read -d $'\0' arg ; do
	if [[ "$arg" == -a* || "$arg" == -[b-zB-Z]*a* || "$arg" == '--all' ]] ; then
		if (( $((unset GIT_INDEX_FILE; git diff --cached --name-only)|wc -l) > 0 )) ; then
			echo 'using --all while files are cached. don'\''t do that.'
			exit 1
		fi
	fi
done < /proc/$PPID/cmdline

Awesome, thanks! For me (11 years later) the pre-commit hook is a subprocess of the git process so I had to add

parent_pid=$(ps -o ppid= $PPID | xargs)

with ps -o ppid= $PPID to get the pid of the parent process and the pipe through xargs to trim a leading whitespace. And then instead of reading from /proc/$PPID/cmdline we read from done < /proc/$parent_pid/cmdline.

Awesome, glad to hear when my random bits get extra life. I've completely forgotten about the --all option for git commit, and i just always do git add -u as a separate stage these days. Also, i've been working on macos most of the time (though looking to switch back to linux), so no procfs for me!