A quick and dirty way of doing it, assuming the currently active pane is the one you want to copy text from:

1. Enable pane zoom (<prefix> z)

2. Enter copy mode (<prefix> [)

3. Select and copy text

You can also look into the tmux-yank [0] plugin, which copies to the native system clipboard.

[0] https://github.com/tmux-plugins/tmux-yank

As other macOS commenter mentioned, total pita, yeah. Under Linux you need this line of command+xsel voodoo: https://wiki.archlinux.org/index.php/Tmux#X_clipboard_integr...

I've tried vi mode copypasting and the copycat plug-in but finally settled for just shift selecting and ctrl+shift+C/V my way through everything.

Edit: for vertical panes ctrl+shift selection works on gnome-terminal at least.

Yeah, it's a pita. I'm sure there must be a plugin that allows thus to work with OS copy buffer but for now I just zoom on a window when I need it and pipe into pbcopy (macOS) for larger things.