Git pre-commit hook to run Rubocop on staged files

pre-commit.zsh

#!/bin/zsh

BRANCH_NAME=$(git branch | grep '*' | sed 's/* //') 

if [[ $BRANCH_NAME != *"no branch"* ]]
then
  FILENAMES=$(git diff --staged --name-only --diff-filter=AM | grep -e "\.rb$" -e "\.rake$")
  if [[ -z "${FILENAMES// }" ]]
  then
    echo "Skipping Rubocop pre-commit hook"
  else
    echo "Running Rubocop pre-commit hook on:"
    echo $FILENAMES
    rubocop --server -A $FILENAMES
  fi
else
  echo "Skipping Rubocop pre-commit hook (rebasing)"
fi