Alt + U is used to undo anything in the nano editor. Alt + E is used to redo anything in the nano editor.

How do I undo a redo in nano?

Starting with nano version 2.3. 5 in July 2014, undo/redo became standard: Alt-U or Option-U or Esc U – undo. Alt-E or Option-E or Esc E – redo.

Is there an undo command in Linux?

There is no undo in the command line. You can however, run commands as rm -i and mv -i .