Zsh: consistent history between machines

Question

Use case: distribute zsh's history between machines in source control.

Is that something that I can achieve with zsh's history -- put history in version control the sync between machines? This is to avoid re-typing commands and quick trace.

Answer 1

Looks like you want BashHub:

Bashhub saves every terminal command entered across all sessions and systems and provides powerful querying across all commands.

Support for Bash and Zsh with a sweet cli for everything.

Edit: If you don't trust the person running the BashHub server for 100% and have commands that should stay private, you should run your own BashHub server.

Answer 2

This is an attempt to answer how to do it using, bash or zsh

In zsh the precmd function is similar to PROMPT_COMMAND in bash, in that it gets executed before each new prompt.

An example using bash:

$ function precmd() {
    echo ssh copy the files to another machine
}
$ export OLD_PROMPT=$PROMPT_COMMAND
$ unset PROMPT_COMMAND && export PROMPT_COMMAND="precmd; $PROMPT_COMMAND"
ssh copy the files to another machine
$ pwd
/home/jmunsch
ssh copy the files to another machine
$ export PROMPT_COMMAND=$OLD_PROMPT

An example using zsh:

% function precmd() {
    echo ssh copy the files to another machine
}
% pwd
/home/jmunsch
ssh copy the files to another machine
% unset -f precmd

Add this to the .zshrc:

function precmd() {
    # across terminals, sessions 
    setopt APPEND_HISTORY
    export machines="192.168.43.70 192.168.43.71 192.168.43.72"
    for m in $machines; do
        scp ~/.zsh_history $m:~/.zsh_history
    done
}

For the .bashrc:

function precmd() {
    # since bash generally saves history on session exit
    history -a # append session to history
    history -c # clear session
    history -r # read from history
    export machines="192.168.43.70 192.168.43.71 192.168.43.72"
    for m in $machines; do
        scp ~/.zsh_history $m:~/.zsh_history
    done
}
export PROMPT_COMMAND="precmd; $PROMPT_COMMAND"

To make it easier to do this

• Setup key based ssh login, or passwordless login.
• Add hostnames/usernames to the .ssh/ssh_config.

related:

• https://superuser.com/questions/410965/command-history-in-zsh
• https://superuser.com/questions/735660/whats-the-zsh-equivalent-of-bashs-prompt-command

Some assumptions about the usage here, is that only 1 person is using 1 session at a time, all machines are online, and all histories get updated successfully.

You might be able to add some additional steps to merge histories, or keep the order of histories.

Using git:

• type a command
• commit changes
• push changes to repo
• on every other machine pull changes

It's not a trivial problem, from what I understand. Say for example you log into two machines with the same history, but then type two different commands in at the same time; do both commands get saved, do the histories diverge, do they overwrite each other?

For further research look into distributed consistency/consensus:

• https://raft.github.io/
• https://en.wikipedia.org/wiki/Paxos_%28computer_science%29
• https://stackoverflow.com/questions/33473513/paxos-algorithm-in-the-context-of-distributed-database-transaction