What is the regex to match a newline character?

Question

In Emacs regex, \n doesn't match a new line character \n.

Am I correct that $ matches the position between a new line character and the character right before the new line character. e.g. for a string abc\n, $ matches the position between c and \n?
What is the regex that matches \n?

Could you provide a minimum working example? Maybe I'm missing something, but (re-search-forward "\n") works fine for me. — Dan, Feb 25 '15 at 00:37
Your file might use \r\n for new lines and it may be that you need to include \r in your regexp, so abc\r\n instead of abc\n. — Jordon Biondo, Feb 25 '15 at 15:53
@Dan: C-M-s and M-x occur both match \n to n. my buffer is in Fundamental mode. This happens to any text, so any text with new line or letter n is a working example — Tim, Feb 27 '15 at 02:17
@Tim, yes because if you are entering them interactively you'd need to do a quoted inserts, C-q C-m, and C-q C-j respectively. You could enter \r\n if you were entering them into a lisp string. — Jordon Biondo, Feb 27 '15 at 03:27
@Dan The string you used, "\n", consists of a single newline character, which certainly matches the newline character! If you wanted to prove that the two character sequence \n matches a newline, you'd need to escape the backslash in the string, i.e., to use (re-search-forward "\\n"). If you do that you'll see that \n matches the letter n. — Omar, Jul 11 '19 at 19:17

score 35 · Answer 1 · answered Feb 25 '15 at 00:00

35

Yes. $ matches the end of the line, not the newline character which comes after the end of the line.
Do C-M-s C-q C-j. C-q is the default binding for quoted-insert and works in the minibuffer too. This expression literally searches for a newline: C-j.

answered Feb 25 '15 at 00:00

Kaushal Modi

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are you saying the new line character can not be represented as an escape sequence in Emacs regex?

Tim

Feb 25 '15 at 00:01

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Whether searching for a newline interactively or via elisp (e.g. (looking-at "^J") where ^J is inserted by C-q C-j), the C-q C-j approach always works. But when using elisp functions like the same looking-at \n works too; M-: (looking-at "\n") RET will eval to true if the cursor is at the end of the line (and there's a newline after that). – Kaushal Modi Feb 25 '15 at 00:09

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Just to mention, if using regexp-builder, you're able to recognize a new line with [\n]. – Nsukami _ Feb 25 '15 at 00:29

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@Nsukami_: C-M-s and M-x occur both match [\n] to n. – Tim Feb 27 '15 at 02:19

score 20 · Answer 2 · answered Feb 25 '15 at 00:56

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As Dan comments, the regex that matches a newline is a newline.

You can represent a newline in a quoted string in elisp as "\n". There is no special additional regexp-specific syntax for this -- you just use a newline, exactly like any other literal character.

If you are entering a regexp interactively then you can insert the newline with C-qC-j, as kaushalmodi's answer points out.

answered Feb 25 '15 at 00:56

phils

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Thanks! In emacs (not in elisp), is C-q C-j the only way to match a new line character? \n doesn't match a new line character. – Tim Apr 09 '15 at 17:10
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Yes. Well, more specifically, typing a newline is the only way to match a newline character when entering a regexp interactively (as there is no regexp escape sequence for a newline), and C-q C-j is the most reliable way to type a newline at a prompt. – phils Apr 09 '15 at 22:21
There can be workarounds, see https://stackoverflow.com/a/20056634/3873799 – alelom Mar 24 '23 at 15:53
@alelom I don't understand what you're trying to say there. That Q&A appears to be about EOL conventions (which vary and may or may not involve carriage return characters), but this question is about matching a newline character. – phils Mar 24 '23 at 23:05

What is the regex to match a newline character?

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