pre-commit git hook to remove trailing whitespace

pre-commit

#!/bin/bash
#
# A git hook script to find and fix trailing whitespace
# in your commits. Bypass it with the --no-verify option
# to git-commit
#
# Logic:
#
# The 'git stash save' fails if the tree is clean (instead of
# creating an empty stash :P). So, we only 'stash' and 'pop' if
# the tree is dirty.
#
# The 'git rebase --whitespace=fix HEAD~' throws away the commit
# if it's empty, and adding '--keep-empty' prevents the whitespace
# from being fixed. So, we first check that the index is dirty.
#
# Also:
# - '(! git diff-index --quiet --cached HEAD)' is true (zero) if
#   the index is dirty
# - '(! git diff-files --quiet .)' is true if the tree is dirty
#
# The 'rebase --whitespace=fix' trick is from here:
# http://stackoverflow.com/a/19156679/470844
#

if (! git diff-files --quiet .) && \
   (! git diff-index --quiet --cached HEAD) ; then
  git commit --quiet --no-verify -m FIXWS_SAVE_INDEX && \
  git stash save --quiet FIXWS_SAVE_TREE && \
  git rebase --quiet --whitespace=fix HEAD~ && \
  git reset --quiet --soft HEAD~ && \
  git stash pop --quiet
elif (! git diff-index --quiet --cached HEAD) ; then
  git commit --quiet --no-verify -m FIXWS_SAVE_INDEX && \
  git rebase --quiet --whitespace=fix HEAD~ && \
  git reset --quiet --soft HEAD~
fi