Git pre-commit hook for Rubocop offenses

pre-commit

#!/bin/sh

# This script only checks the total number of offenses in modified files.
# If you removed old offenses, it may not warn you about new ones.

# Other scripts check all modified files for offenses.
# They don't ignore old offenses.

NUMBER_BEFORE=`git diff --cached --diff-filter=CMRTUXB --name-only -- '*.rb' | sed 's/^\(.*\)$/HEAD:\1/' | xargs git show | rubocop -s head -f o | tail -n 2 | head -n 1 | cut -d ' ' -f 1`
NUMBER_NOW=`git diff --cached --diff-filter=ACMRTUXB --name-only -- '*.rb' | xargs cat | rubocop -s now -f o | tail -n 2 | head -n 1 | cut -d ' ' -f 1`

if [ "$NUMBER_BEFORE" -lt "$NUMBER_NOW" ]; then
  echo "You have $NUMBER_NOW offenses now. There were $NUMBER_BEFORE before."
  echo "Display all offenses of modified files by running:"
  echo "  git diff --diff-filter=ACMRTUXB --name-only | xargs rubocop"
  exit 1
fi