determining the line terminator in Emacs

StackOverflow https://stackoverflow.com/questions/234479

  •  04-07-2019
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Question

I'm writing a config file and I need to define if the process expects a windows format file or a unix format file. I've got a copy of the expected file - is there a way I can check if it uses \n or \r\n without exiting emacs?

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Solution

If it says (DOS) on the modeline when you open the file on Unix, the line endings are Windows-style. If it says (Unix) when you open the file on Windows, the line endings are Unix-style.

From the Emacs 22.2 manual (Node: Mode Line):

If the buffer's file uses carriage-return linefeed, the colon changes to either a backslash ('\') or '(DOS)', depending on the operating system. If the file uses just carriage-return, the colon indicator changes to either a forward slash ('/') or '(Mac)'. On some systems, Emacs displays '(Unix)' instead of the colon for files that use newline as the line separator.

Here's a function that – I think – shows how to check from elisp what Emacs has determined to be the type of line endings. If it looks inordinately complicated, perhaps it is.

(defun describe-eol ()
  (interactive)
  (let ((eol-type (coding-system-eol-type buffer-file-coding-system)))
    (when (vectorp eol-type)
      (setq eol-type (coding-system-eol-type (aref eol-type 0))))
    (message "Line endings are of type: %s"
             (case eol-type
               (0 "Unix") (1 "DOS") (2 "Mac") (t "Unknown")))))

OTHER TIPS

If you go in hexl-mode (M-x hexl-mode), you shoul see the line termination bytes.

Open the file in emacs using find-file-literally. If lines have ^M symbols at the end, it expects a windows format text file.

The following Elisp function will return nil if no "\r\n" terminators appear in a file (otherwise it returns the point of the first occurrence). You can put it in your .emacs and call it with M-x check-eol.

(defun check-eol (FILE)
  (interactive "fFile: ")
  (set-buffer (generate-new-buffer "*check-eol*"))
  (insert-file-contents-literally FILE)
  (let ((point (search-forward "\r\n")))
    (kill-buffer nil)
    point))
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