Ruby script: Find the current git repository

find_git_repo.rb

# Script: Find the current git repository
# Based on https://github.com/mojombo/grit/pull/178 by https://github.com/derricks

# Be sure to "gem install grit" before running this script
require 'grit'

# Returns true if the given path represents a root directory (/ or C:/)
def root_directory?(file_path)
  # Implementation inspired by http://stackoverflow.com/a/4969416:
  # Does file + ".." resolve to the same directory as file_path?
  File.directory?(file_path) && 
    File.expand_path(file_path) == File.expand_path(File.join(file_path, '..'))
end

# Returns the git root directory given a path inside the repo. Returns nil if
# the path is not in a git repo.
def find_git_repo(start_path = '.')
  raise NoSuchPathError unless File.exists?(start_path)

  current_path = File.expand_path(start_path)

  # for clarity: set to an explicit nil and then just return whatever
  # the current value of this variable is (nil or otherwise)
  return_path = nil

  until root_directory?(current_path)
    if File.exists?(File.join(current_path, '.git'))   
      # done
      return_path = current_path
      break
    else
      # go up a directory and try again
      current_path = File.dirname(current_path)
    end
  end
  return_path
end

# Returns a new Grit::Repo instance for the repo that has the given path.
# Returns nil if the path is not in a git repo.
def find_grit_repo(start_path = '.')
  path = find_git_repo start_path

  path.nil? ? nil : Grit::Repo.new(path)
end

# Command line interface (for testing)
puts find_git_repo(ARGV.first || '.') || '[no results]'

test.rb

def test_new_should_work_in_subdirectory
  tmpdir = Dir.mktmpdir
  gpath = File.join(tmpdir, '.git')
  subdir_path = File.join(tmpdir, 'test_subdirectory')

  FileUtils.mkdir_p(gpath)
  FileUtils.mkdir_p(subdir_path)

  assert(Repo.new(subdir_path))

  FileUtils.rm_rf(tmpdir)
end