How to loop over every line in a buffer?

Question

I am searching for some kind of reduce function, which loops through every line of a buffer, but I can not find it. Does anybody know the name of such a function?

Something similar to Perl

while (<>) {
  ...
}

Or a dolist for buffer lines.

Found just this: https://github.com/Wilfred/loop.el#loop-for-each-line — ceving, Feb 01 '18 at 08:34

score 10 · Accepted Answer · answered Jan 31 '18 at 17:50

10

A slightly more idiomatic example:

(goto-char (point-min))
(while (not (eobp))
  ...
  (forward-line 1))

answered Jan 31 '18 at 17:50

wasamasa

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See also https://emacs.stackexchange.com/a/19538/15748. – Basil Feb 02 '18 at 01:04

score 6 · Answer 2 · answered Jan 31 '18 at 14:36

You can make a while loop using the function forward-line as your test. If forward-line reaches the end of the buffer, it returns the number of lines it wanted to move but couldn't. That leads to the following loop:

(save-excursion  ;; save our starting position
  (goto-char (point-min))    ;; go to the beginning of the buffer
  (while (< (forward-line) 1)    ;; move forward one line
                                 ;; until forward line returns a non-zero value
    (end-of-line)    ;; go to the end of the line
    (insert ";; I made it to here!")))    ;; insert a comment

The while loop continues as long as forward-line returns 0, which it does when it is able to move. It will return 1 when it can't move any further.

Does this skip the first line? – ceving Feb 02 '18 at 07:56 — ceving, Feb 02 '18 at 07:56

How to loop over every line in a buffer?

2 Answers2