Transient prompt with Zsh

Vincent Bernat

Powerlevel10k is a theme for Zsh. It contains some powerful features, is astoundingly fast, and easy to customize. I am quite amazed at the skills of its main author. Be sure to also have a look at Zsh for Humans, a complete Zsh configuration including this theme.

One of the nice features of Powerlevel10k is transient prompts: past prompts are reduced to a more minimal configuration to save space by removing unneeded information.

Demonstration of a transient prompt with Zsh: past prompts use a
more compact form
My implementation of a transient prompt with Zsh. Past prompts are compact and include the time of the command execution, the hostname, and the status of the previous command while the complete prompt contains more information like the current directory and the Git branch.

When it comes to configuring my shell, I still prefer writing and understanding each line going into it. Therefore, I am still building my Zsh configuration from scratch. Here is how I have integrated the above transient feature into my prompt.

The first step is to configure the appearance of the prompt in its compact form. Let’s assume we have a variable, $_vbe_prompt_compact set to 1 when we want a compact prompt. We use the following function to define the prompt appearance:

_vbe_prompt () {
    local retval=$?

    # When compact, just time + prompt sign
    if (( $_vbe_prompt_compact )); then
        # Current time (with timezone for remote hosts)
        _vbe_prompt_segment cyan default "%D{%H:%M${SSH_TTY+ %Z}}"
        # Hostname for remote hosts
        [[ $SSH_TTY ]] && \
            _vbe_prompt_segment black magenta "%B%M%b"
        # Status of the last command
        if (( $retval )); then
            _vbe_prompt_segment red default ${PRCH[reta]}
            _vbe_prompt_segment green cyan ${PRCH[ok]}
        # End of prompt

    # Regular prompt with many information
    # […]
setopt prompt_subst
PS1='$(_vbe_prompt) '

Update (2021-05)

The following part has been rewritten to be more robust. The code is stolen from Powerlevel10k’s issue #888. See the comments for more details.

Our next step is to redraw the prompt after accepting a command. We wrap Zsh line editor into a function:1

_vbe-zle-line-init() {
    [[ $CONTEXT == start ]] || return 0

    # Start regular line editor
    (( $+zle_bracketed_paste )) && print -r -n - $zle_bracketed_paste[1]
    zle .recursive-edit
    local -i ret=$?
    (( $+zle_bracketed_paste )) && print -r -n - $zle_bracketed_paste[2]

    # If we received EOT, we exit the shell
    if [[ $ret == 0 && $KEYS == $'\4' ]]; then
        zle .reset-prompt

    # Line edition is over. Shorten the current prompt.
    zle .reset-prompt
    unset _vbe_prompt_compact

    if (( ret )); then
        # Ctrl-C
        zle .send-break
        # Enter
        zle .accept-line
    return ret
zle -N zle-line-init _vbe-zle-line-init

That’s all!

One downside of using the powerline fonts is that it messes with copy/paste. As I am using tmux, I use the following snippet to work around this issue and use only standard Unicode characters when copying from the terminal:

bind-key -T copy-mode M-w \
  send -X copy-pipe-and-cancel "sed 's/.*/%/g' | xclip -i -selection clipboard" \;\
  display-message "Selection saved to clipboard!"

Copying and pasting the text from the screenshot above yields the following text:

14:21 % ssh
Linux eizo 4.19.0-16-amd64 #1 SMP Debian 4.19.181-1 (2021-03-19) x86_64
Last login: Fri Apr 23 14:20:39 2021 from 2a01:cb00:3f:b02:9db6:efa4:d85:7f9f
14:21 CEST % uname -a
Linux eizo 4.19.0-16-amd64 #1 SMP Debian 4.19.181-1 (2021-03-19) x86_64 GNU/Linux
14:21 CEST %
Connection to closed.
14:22 % git status
On branch article/zsh-transient
Untracked files:
  (use "git add <file>..." to include in what will be committed)

nothing added to commit but untracked files present (use "git add" to track)

  1. We have to manually enable bracketed paste because Zsh does it after zle-line-init↩︎