github hook

hook.sh

On Mac OS (or, likely, any BSD), the sed command parameters have to be slightly different. Try this:

#!/bin/sh

if git-rev-parse --verify HEAD >/dev/null 2>&1 ; then
   against=HEAD
else
   # Initial commit: diff against an empty tree object
   against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
fi

# Find files with trailing whitespace
for FILE in `exec git diff-index --check --cached $against -- | sed '/^[+-]/d' | sed -E 's/:[0-9]+:.*//' | uniq` ; do
    # Fix them!
    sed -i '' -E 's/[[:space:]]*$//' "$FILE"
    git add "$FILE"
done
Save this file as .git/hooks/pre-commit -- or look for the one that's already there, and paste the bottom chunk somewhere inside it. And remember to chmod a+x it too.

This is taken from http://stackoverflow.com/a/4597057/1560470