Emacs Lisp: Functions on Line

By Xah Lee. Date: . Last updated: .

Get Position of Beginning of Line

line-beginning-position
(line-beginning-position &optional N)

Return the character position of the first character on the current line.

With optional argument N, scan forward N - 1 lines first.

If the scan reaches the end of the buffer, return that position. 

;; return line beginning position
(line-beginning-position)
line-end-position
(line-end-position &optional N) like line-beginning-position but return the line end position.

Move Cursor to Beginning of Line

beginning-of-line
(beginning-of-line &optional N)
  • Move point to beginning of current line.
  • With argument N not nil or 1, move forward N - 1 lines first.
  • If point reaches the beginning or end of buffer, it stops there.
;; move cursor to beginning of current line
(beginning-of-line)
;; better than (goto-char (line-beginning-position))
end-of-line
(end-of-line &optional N)
  • Move point to end of current line.
  • With argument N not nil or 1, move forward N - 1 lines first.
  • If point reaches the beginning or end of buffer, it stops there.

Tip: Do not use (search-forward "\n") for moving cursor to end of line. Because you'll have special cases if the line is at the end of buffer and doesn't have a newline char. It is also slower.

Tip: Do not use move-beginning-of-line or move-end-of-line. Because these are designed for interactive use.

Move Cursor to Next Line

forward-line
(forward-line &optional N)
  • Move cursor to the next line, or N lines.
  • N default to 1.
  • If N is negative, move in the other direction.
  • Cursor ends at the beginning of line.
;; move cursor to previous line, and at the beginning
(forward-line -1)

Tip: Do not use next-line or previous-line. Because these are for interactive use. Their behavior changes depending on the variable line-move-visual.

Get Current Line as String

To grab current line, use:

(setq myLine
      (buffer-substring-no-properties
       (line-beginning-position)
       (line-end-position)
       ))

Tip: Do not use (thing-at-point 'line). Normally, thing-at-point will include the newline char, but if the line is at the end of buffer, then it won't. So, if you use it, you have to do extra work to detect special cases. Also, thing-at-point is complex elisp code and is slower. [see Emacs Lisp: Using thing-at-point]

Get All Lines in a File into a List

Emacs Lisp: Read File Content as String or List of Lines

See also: Process a File line-by-line in Emacs Lisp.

Screen Lines

If you want to move cursor across lines as defined by the screen (wrapped at edge of screen), you can use these.

What Character Does Emacs Use for Newline

In emacs buffer, newline char is "\n", in any operating system (Mac, Linux, Microsoft Windows ). So, you can use (search-forward "\n"). However, if you are on the last line, there may not be a ending "\n".

~2010 Thanks to Uday S Reddy [http://www.cs.bham.ac.uk/~udr/] and Alan Mackenzie [http://www.emacswiki.org/emacs/AlanMackenzie] for tips.