How to set key binding to `C-c C-t` in `sh-mode`?

Question

By default C-c C-t has sh-tmp-file binding in sh-mode, which I want to change.:

C-c C-t runs the command sh-tmp-file (found in sh-mode-map), which is an
interactive compiled Lisp function in ‘sh-script.el’.

It is bound to C-c C-t.

I have tried to bind the key binding as follows:

(defun insert-todo ()
  (interactive "*")
  (insert comment-start "TODO: "))

(define-key shell-mode-map (kbd "C-c C-t") 'insert-todo)
(define-key sh-mode-map (kbd "C-c C-t") 'insert-todo)

---

I am having following error message:

Debugger entered--Lisp error: (void-variable sh-mode-map)
  (define-key sh-mode-map (kbd "C-c C-t") 'insert-todo)
  eval-buffer(#<buffer  *load*> nil "/home/alper/.emacs" nil t)  ; Reading at
buffer position 100039
  load-with-code-conversion("/home/alper/.emacs" "/home/alper/.emacs" t t)
  load("~/.emacs" noerror nomessage)
  startup--load-user-init-file(#f(compiled-function () #<bytecode
0x15948fd477f1>) #f(compiled-function () #<bytecode
0x15948fd46d41>) t)
  command-line()
  normal-top-level()

How could I resolve this error?

Answer 1

Mode keymaps aren't defined until the defining library has been loaded, so you just need to defer binding the key until that happens.

(with-eval-after-load "sh-script"
  (define-key sh-mode-map (kbd "C-c C-t") 'insert-todo))