goto-line-with-feedback.el

;; turn line numbers off by default
(global-linum-mode -1)

(defun goto-line-with-feedback (&optional line)
  "Show line numbers temporarily, while prompting for the line number input"
  (interactive "P")
  (if line
    (goto-line line)
    (progn
      (linum-mode 1)
      (let ((line (read-number "Line: ")))
        (goto-line line))
      (linum-mode -1))))

(global-set-key (kbd "C-l") 'goto-line-with-feedback)

To do:

• is there any worth in making this a global minor mode?
• when you activate line numbers, and then exit (eg. C-g) the line numbers stay visible. Is there a way to catch the exit?

You can use unwind-protect:

(defun goto-line-with-feedback (&optional line)
  "Show line numbers temporarily, while prompting for the line number input"
  (interactive "P")
  (if line
      (goto-line line)
    (unwind-protect
        (progn
          (linum-mode 1)
          (let ((line (read-number "Line: ")))
            (goto-line line)))
          (linum-mode -1))))

@pragdave Why are you using linum-mode, instead of the built-in line numbers that Eli Z. implemented starting from Emacs 26 and forwards? linum-mode is officially deprecated. The replacement is display-line-numbers-mode / global-display-line-numbers-mode: https://www.gnu.org/software/emacs/manual/html_node/emacs/Display-Custom.html