To copy & paste in nano text editor: 1. Move cursor to start of text and press CTRL + 6 to set mark. 2. Highlight text to copy using arrow keys. 3. Press ALT + 6 to copy. 4. Move cursor to desired location and press CTRL + U to paste.
Starting with nano version 2.3.5 in July 2014, undo/redo became standard: Alt-U or Option-U or EscU - undo Alt-E or Option-E or EscE - redo