I run the following codes separately as my prompt unsuccessfully in .zshrc. This suggests me that apparently I do not have a program called __git_ps1. It is not in MacPorts.

#1

PROMPT="$(__git_ps1 " \[\033[1;32m\] (%s)\[\033[0m\]")\$"$

#2

PROMPT="$(__git_ps1 " (%s)")\$"$

#3

# Get the name of the branch we are on
git_prompt_info() {
  branch_prompt=$(__git_ps1)
  if [ -n "$branch_prompt" ]; then
    status_icon=$(git_status)
    echo $branch_prompt $status_icon
  fi
}

# Show character if changes are pending
git_status() {
  if current_git_status=$(git status | grep 'added to commit' 2> /dev/null); then
    echo "?"
  fi
}
autoload -U colors
colors
setopt prompt_subst
PROMPT='
%~%{$fg_bold[black]%}$(git_prompt_info)
? %{$reset_color%}'

How can you get a prompt which shows the name of a Git-branch?