I've been asking question about this, but it seems that my Minecraft on Mac can't accept to copy/paste/select from Minecraft to Minecraft itself or from Minecraft to my Mac; however, I can copy from my Mac to Minecraft using
Cmd + v.
For more precision, I am using the latest version of Minecraft, the
1.9.2, my Mac computer version is the
MacBook Air (13-inch, Early 2015), and my Mac system version is the
OS X El Capitan.