How can I get ZSH shared history to work?

Question

I have setopt share_history and set opt inc_append_history set in my ~/.zshrc. This is almost working.

In session 1, I execute a command, it's written to history.

In session 2, the command is not visible when I press the UP arrow, until I execute history. Once I execute history it appears.

How can I get history to show up immediately when I press the UP arrow?

Answer 1

When the Z shell displays the prompt it is idle and IMHO does not do any background tasks. So, the history file $HISTFILE is re-read only when rendering a new prompt. That why it is sufficient, but also necessary that you press ENTER in a terminal to re-read your history.

If you you want to save this additional keystroke you can use the following zle widget in your ~/.zshrc:

up-line-or-history-reread() {
        [[ -z $BUFFER ]] && fc -R $HISTFILE
        zle up-line-or-history
}
zle -N up-line-or-history-reread
bindkey '^[[A' up-line-or-history-reread

This new widget, which is bound to UP ARROW, checks if the current command line is empty and if so re-reads the history. After that it invokes the default widget (up-line-or-history).

This approach has at least these two flaws compared to the default behavior:

• If you're up in the history a few command, and delete the entire command line, the next press on UP ARROW starts again at the end of the command history.
• If you use some other history machanism, like history search, you still need to press the ENTER key before or you write a similar widget for these purposes, too.