How to save and restore the default prompt (when PS1 is not defined)?

Question

In a shared cluster I work on, the environment settings for new accounts does not include a prompt setting, as far as I can tell. In particular, PS1 is not set. And yet, when one logs into a new account, one gets a rather fancy prompt, featuring the username and the basename of the current directory.

I want to save this prompt (e.g. in an environment variable like ORIGINAL_PS1) before replacing it with my preferred prompt, so that I can restore it later if desired¹.

How can I extract the prompt definition from the current prompt?

I am primarily interested in the answer to this question for bash, but if there's something analogous for zsh, please let me know.

---

^{1 I rather like the default prompt, but for everyday use I prefer to use a "git-aware" prompt. That said, although I find the latter extremely helpful 99.999% of the time, ocassionally I cd to a git repo that is sufficiently messed up that it causes the prompt's generation to become unacceptably slow. For those rare circumstances, I'd like to be able to run export PS1=$ORIGINAL_PS1.}

Answer 1

ORIGINAL_PS1=$PS1 would save the value of the primary prompt variable to a new variable.

The PS1 variable is a shell variable that is not exported, i.e. it's not an environment variable that is inherited by child processes.

In the zsh shell, you may want to additionally save the "right primary prompt", RPS1, if that is used. The primary prompt is called PS1 in zsh, just as in bash.