Pre-commit hook for git which removes trailing whitespace, converts tabs to spaces and adds a newline to the end of the file if missing.

fix_whitespace.rake

script_file = File.join(Rails.root, "script", "git_fix_whitespace.sh")

desc "Remove trailing whitespace and convert tabs to spaces"
task :fix_whitespace do
  `sh #{script_file} -f`
end

namespace :fix_whitespace do
  desc "Installs a git pre-commit hook which removes trailing whitespace and converts tabs to spaces"
  task :install, :force do |t, args|
    if !args.force && File.size?(".git/hooks/pre-commit")
      abort '.git/hooks/pre-commit already exists. Install with "rake fix_whitespace:install[true]"'
    else
      puts "Installing .git/hooks/pre-commit ..."
      FileUtils.mkdir_p "#{Rails.root}/.git/hooks"
      FileUtils.cp script_file, ".git/hooks/pre-commit"
      File.chmod(0755, ".git/hooks/pre-commit")
    end
  end
end

git_fix_whitespace.sh

#!/bin/sh
# Pre-commit hook for git which removes trailing whitespace, converts tabs to
# spaces and adds a newline to the end of the file if missing. The script does
# not process files that are partially staged. Reason: The `git add` in the last
# line would fully stage a file which is not what the user wants.

if git rev-parse --verify HEAD >/dev/null 2>&1 ; then
   against=HEAD
else
   # Initial commit: diff against an empty tree object
   against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
fi

if [ "$1" == "-f" ]; then
   # Fix all committed files: diff against an empty tree object
   against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
fi

staged_files=`git diff-index --name-status --cached $against | # Find all staged files
              egrep -i '^(A|M)'                              | # Filter only added and modified files
              sed -e 's/^[AM][[:space:]]*//'`                  # Remove leading git info

partially_staged_files=`git status --porcelain --untracked-files=no | # Find all staged files
                        egrep -i '^(A|M)M'                          | # Filter only partially staged files
                        sed -e 's/^[AM]M[[:space:]]*//'`              # Remove leading git info

# Merge staged files and partially staged files
staged_and_partially_staged_files=${staged_files}$'\n'${partially_staged_files}

# Remove all files that are staged *AND* partially staged
# Thus we get only the fully staged files
fully_staged_files=`echo "$staged_and_partially_staged_files" | uniq -u`

# Find the file types we want to process
suffix_matched_files=`echo "$fully_staged_files" |
                        egrep -i '\.(rb|rake|ru|erb|haml|rabl|js|json|html|yml|xml|md|txt|sh|sublime-project)$' |
                        egrep -v 'vcr_cassettes'`

name_matched_files=`echo "$fully_staged_files" |
                      egrep -i '^(README|Gemfile|Capfile|Guardfile|Rakefile|\.gitignore)$' |
                      egrep -v 'vcr_cassettes'`

files_to_process=${suffix_matched_files}$'\n'${name_matched_files}
files_to_process=`echo "$files_to_process" | sort | uniq -u`

# Change field separator to newline so that for correctly iterates over lines
IFS=$'\n'

for FILE in $files_to_process ; do
    echo "Fixing whitespace and newline in $FILE" >&2

    # Replace tabs with four spaces
    sed -i '' $'s/\t/    /g' "$FILE"

    # Strip trailing whitespace
    sed -i '' -E 's/[[:space:]]*$//' "$FILE"

    # Add newline to the end of the file if missing
    newline='
'
    lastline=$(tail -n 1 ${FILE}; echo x); lastline=${lastline%x}
    [ "${lastline#"${lastline%?}"}" != "$newline" ] && echo >> $FILE

    # Stage all changes
    git add "$FILE"
done