Pre-commit hook to remove trailing whitespace on lines you've actually changed

gistfile1.txt

#
# Shamelessly copied from http://blog.yesmeck.com/archives/make-git-automatically-remove-trailing-whitespace-before-committing/
#
# What's distinct about this version, as opposed to several I've seen,
# is that it only fixes the whitespace on lines you've actually changed,
# so avoids making you the blamee of code you didn't change.

# Find files with trailing whitespace
for file in `git diff --check --cached | grep '^[^+-]' | grep -o '^.*[0-9]\+:'` ; do
    file_name=`echo ${file} | grep -o '^[^:]\+'`
    line_number=`echo ${file} | grep -oP '(?<=:)[0-9]+(?=:)'`
    # I think the reason there are two sed commands here
    # is that 'sed -i' is different on different systems.
    # shoot me.
    (sed -i "${line_number}s/\s*$//" "${file_name}" > /dev/null 2>&1 \
        || sed -i '' -E "${line_number}s/\s*$//" "${file_name}")
    git add ${file_name}
    echo "Re-wrote ${file_name} to trim whitespace."
done

# Now we can commit
exit