Question

I like format all my code using tab instead of space, but I just want to convert spaces to tabs at the beginning of each lines.

Can tabify just convert space to tabs at the beging of lines?

Answer 1

The documentation for tabify mentions a suitable value for operating on line-leading whitespace only. I used it to write this function which I find handy, but you could just set it in your init file and forego a separate function:

(defun tabify-leading (start end)
  "Call `tabify' with `tabify-regexp' set so that only leading
spaces are treated."
  (interactive "r")
  (setq tabify-regexp-old tabify-regexp)
  (unwind-protect
      (progn
        (setq tabify-regexp "^\t* [ \t]+")
        (tabify start end))
    (setq tabify-regexp tabify-regexp-old)))