TL;DR

script

autoload -Uz add-zsh-hook

rbenv_version () {
  local ruby_v=$(rbenv version-name)
  if [[ "`rbenv version | grep '.rbenv/version'`" = "" ]];then
    if [[ "`rbenv version | grep 'RBENV_VERSION'`" = "" ]];then
      local setting="%{$fg[green]%}[$ruby_v (local)]%{$reset_color%}"
    else
      local setting="%{$fg[blue]%}[$ruby_v (global)]%{$reset_color%}"
    fi
  else
    local setting="%{$fg[blue]%}[$ruby_v (global)]%{$reset_color%}"
  fi
  RPROMPT="$setting"
}
add-zsh-hook precmd rbenv_version