fish history sync

I use fish in tmux with maybe two dozen shells open at a time, for various projects that I have hanging around. By adding

# history across fishes
function save_history --on-event fish_preexec
    history --save
end
alias hr 'history --merge'  # read and merge history from disk
bind \e\[A 'history --merge ; up-or-search'

to ~/.config/fish/config.fish, reverse search now syncs across all history in all shells (or you can bring a shell up to date with all other shells using hr). That feels good.