A Git Pre-Commit hook to run the Rubocop static code analyzer. I'm not saying this is a Good Idea™. In fact, it's a Bad Idea™; integrate linting/formatting with your editor/IDE instead. Use at your own risk. If it breaks, feel free to keep both pieces.

pre-commit.sh

#!/usr/bin/env bash

set -eu

RED='\033[0;31m'
GREEN='\033[0;32m'
YELLOW='\033[0;33m'
NO_COLOR='\033[0m'
CLEAR_LINE='\r\033[K'

printf "🚔    Linting with Rubocop..."

if ! command -v bin/rubocop > /dev/null; then
  printf "${CLEAR_LINE}💀${RED}   Install Rubocop and be sure it is available on your PATH${NO_COLOR}\n"
  printf "ℹ️   Try 'gem install rubocop'\n"
  exit -1
fi

suspects="$(comm -12 <(git diff --cached --name-only --diff-filter=AMC | sort) <(rubocop --list-target-files | sort) | tr '\n' ' ')"

if [ -n "$suspects" ]; then
  if [[ ! -f .rubocop.yml ]]; then
    printf "${CLEAR_LINE}${YELLOW}⚠️   No .rubocop.yml config file.${NO_COLOR}\n"
  fi

  printf "${CLEAR_LINE}🚔   Linting files: ${suspects}"

  # Run rubocop on the staged files
  if ! bin/rubocop --parallel --format simple ${suspects} > /dev/null
  then
    printf "${CLEAR_LINE}${RED}💀   Rubocop found some issues. Fix, stage, and commit again${NO_COLOR}\n"
    printf "ℹ️   Try 'bin/rubocop --display-cop-names --extra-details --auto-correct && git add -p'\n"
    exit -1
  fi
fi

printf "${CLEAR_LINE}🎉${GREEN}   Rubocop is appeased.${NO_COLOR}\n"
exit 0

This is great!

Thanks for sharing it.

@stevenharman