Robustly change to the root of a git repository (http://codereview.stackexchange.com/questions/138255/robust-bash-function-to-find-the-root-of-a-git-repository)

cd_git_root.sh

# Print the name of the git repository's working tree's root directory
# Search for 'Tom Hale' in http://stackoverflow.com/questions/957928/is-there-a-way-to-get-the-git-root-directory-in-one-command
# Or, shorter: 
# (root=$(git rev-parse --git-dir)/ && cd ${root%%/.git/*} && git rev-parse && pwd)
# but this doesn't cover external $GIT_DIRs which are named other than .git
function git_root {
  local root first_commit
  # git displays its own error if not in a repository
  root=$(git rev-parse --show-toplevel) || return
  if [[ -n $root ]]; then
    echo "$root"
    return
  elif [[ $(git rev-parse --is-inside-git-dir) = true ]]; then
    # We're inside the .git directory
    # Store the commit id of the first commit to compare later
    # It's possible that $GIT_DIR points somewhere not inside the repo
    first_commit=$(git rev-list --parents HEAD | tail -1) ||
      echo "$0: Can't get initial commit" 2>&1 && false && return
    root=$(git rev-parse --git-dir)/.. &&
      # subshell so we don't change the user's working directory
    ( cd "$root" &&
      if [[ $(git rev-list --parents HEAD | tail -1) = "$first_commit" ]]; then
        pwd
      else
        echo "${FUNCNAME[0]}: git directory is not inside its repository" 2>&1
        false
      fi
    )
  else
    echo "${FUNCNAME[0]}: Can't determine repository root" 2>&1
    false
  fi
}

# Change working directory to git repository root
function cd_git_root {
  local root
  root=$(git_root) || return $? # git_root will print any errors
  cd "$root" || return $?
}