I'd tried using iTerm2 beta Build 18.104.22.16820724 and using
bind C-y run-shell "reattach-to-user-namespace -l zsh -c 'tmux show-buffer | pbcopy'" in .tmux.conf but none works.
The solutions I found aren't specific about the system and conditions. Hence I hope the problem statement here is clear ie. Copying text from remote to OS X clipboard via iTerm2 with Tmux.
Copy text output from cat of a log file that's longer than a screen.
Copy text from vertically* split screen (left and right panes) without copying the text from the other pane.
*not sure if it should be called vertically or horizontally split.
Copy text through Vim that's longer than a screen.
I'm aware of holding alt while clicking and drag to select the text. But the problem arises when you need to scroll, or are working in more than 1 pane.