zsh random color in PS1

Question

My .bashrc PS1 (abridged) is

\u\[\e[01;3$(($RANDOM % 8))m\]@\h \w $'

With the way bash works, it interpolates the random color after each command so the @ is a different color each time (at least in the 31-37 range).

However, I've been unable to do something similar in zsh. The $'' syntax does not allow for command substitution, and concatenating does not work either:

$'\e[01;3'$(($RANDOM % 8))
# The \e[01;3 character is printed first, then the random number

Using quotes " does not work either; it just prints out a literal \e...

I know that zsh also has some built in text colors like %{$fg[red]%} and I could somehow select a random color from the array, but the problem is that it needs to be randomly selected by the PS1 and not simply on start up or the random choice will be made only once.

Is there any way I can interpolate a random number in the PS1 in zsh to achieve this?

Answer 1

You can use a precmd hook which will be evaluated before each prompt:

randomise_prompt_colour () {
  PS1="%n%B%F{$((RANDOM % 8))}@%m %~ %(!.#.\$) "
}

add-zsh-hook precmd randomise_prompt_colour