如何在ZSH提示中输出当前历史记录事件编号（％！或％h）-1？

Question

In my ZSH prompt I want to be able to output the current history event number ( %! or %h ) -1

If current history event number is !256, I want to subtract it by one and output the result in my prompt (ie !255).

Here's the way it looks now and how I'd like it to be:

Below is my current ZSH theme (and the code pertaining to this question lies in the previous_history_event_number () function, which is triggered from the return_code_enabled= declaration:

# ------------------------------------------------------------------------------
#          FILE:  hced.zsh-theme
#   DESCRIPTION:  oh-my-zsh theme file.
#                 (Credits to authors of blinks.zsh-theme and dieter.zsh-theme
#                  from which themes I've taken useful bits.)
#        AUTHOR:  hced
#       VERSION:  0.0.1
#    SCREENSHOT:
# ------------------------------------------------------------------------------

function _prompt_char() {
  if $(git rev-parse --is-inside-work-tree >/dev/null 2>&1); then
    echo "%{%F{blue}%}±%{%f%k%b%}"
  else
    echo ' '
  fi
}

ZSH_THEME_GIT_PROMPT_PREFIX=" [%{%B%F{blue}%}"
ZSH_THEME_GIT_PROMPT_SUFFIX="%{%f%k%b%K{black}%B%F{green}%}]"
ZSH_THEME_GIT_PROMPT_DIRTY=" %{%F{red}%}*%{%f%k%b%}"
ZSH_THEME_GIT_PROMPT_CLEAN=""

PROMPT='%{%f%k%b%}
%{%K{black}%B%F{green}%}%n%{%B%F{blue}%}@%{%B%F{cyan}%}%m%{%B%F{green}%} %{%b%F{yellow}%K{black}%}%~%{%B%F{green}%}$(git_prompt_info)%E%{%f%k%b%}
%{%K{black}%}$(_prompt_char)%{%K{black}%} %#%{%f%k%b%} '

#RPROMPT='!%{%B%F{cyan}%}%!%{%f%k%b%}'

function previous_history_event_number () {
    prev_hist_num=("%!"-1)
    declare -i prev_hist_num
    echo "$prev_hist_num gave exit code: "
}

# elaborate exitcode on the right when >0
return_code_enabled="%(?..%{$fg[red]%}$(previous_history_event_number)%?%{$reset_color%})"
return_code_disabled=
return_code=$return_code_enabled

RPS1='${return_code}  !%{%B%F{cyan}%}%!%{%f%k%b%}'

function accept-line-or-clear-warning () {
    if [[ -z $BUFFER ]]; then
        time=$time_disabled
        return_code=$return_code_disabled
    else
        time=$time_enabled
        return_code=$return_code_enabled
    fi
    zle accept-line
}
zle -N accept-line-or-clear-warning
bindkey '^M' accept-line-or-clear-warning

Disclaimer: I'm not a programmer so the code within the previous_history_event_number () function is pretty (vastly) clueless right now.

Answer 1

If current history event number is shown when you add %! atom in a prompt then you can get it into a variable by using (%) modifier:

V='%!'
integer HISTORY_EVENT_NUMBER=${(%)V}-1