git pre-commit warning to trailing whitespaces

pre-commit

#!/bin/sh

function error() {
  echo "'$1' has trailing spaces.\n" >&2
}

git diff --cached --name-only | (while read f; do
  ERROR=0
  if grep -n '[[:space:]]$' "$f" ; then
    error $f
    ERROR=1
  fi
done; exit $ERROR)

if [ $? -eq 0 -o "$IGNORE_WHITESPACE" ]; then
  exit
else
  echo "if you know what you are doing, use 'IGNORE_WHITESPACE=1 git commit'"
  exit 1
fi

You need to put this in the project's .git/hooks directory, make sure it's executable using chmod a+x .git/hooks/pre-commit

/bin/sh on Ubuntu is the dash shell and the function error() definition doesn't work; one fix is to change the first line to /bin/bash.

To automatically add this to projects, read about TEMPLATE DIRECTORY in git-init help.