This is a fish plugin that modifies built-in up-or-search command to merge the command history.
The effect is that shell command history becomes shared across all open shells.
Original implementations by @farcaller from fish-shell/fish-shell#825 (comment)
If using fundle add the following to ~/.config/fish/config.fish before fundle init:
fundle plugin '2m/fish-history-merge'then reload fish shell and then run fundle install.
If using fisher run fisher install 2m/fish-history-merge.