Often I need to use regular expressions to match strings across multiple lines. In python and other languages, it's possible to ask that dots match newlines (as opposed to the default behavior). Is it possible to do this using the default regexp utilities without hacking the source?
I know I can use a negated character class, which will consume newlines if the newline is not in the class, but this is too limited since what I really want is to just match any character at all.
While erjoalgo's answer is correct, according to the Emacs Wiki Mutliline Regex page, it is not the most efficient answer:
To match any number of characters, use this:
.*– the problem is that.matches any character except newline. What many people propose next works, but is inefficient if you assume that newlines are not that common in your text:"\\(.\\|\n\\)". Better match multiple lines instead:"\\(.*\n?\\)*". The newline is optional so that the expression can end in the middle of a line. Better yet:"[\0-\377[:nonascii:]]*"avoids “Stack overflow in regexp matcher” for huge texts, e.g., > 34k.
"[\0-\377[:nonascii:]]*" rather than "[\0-\177[:nonascii:]]*" (or, moreover, "[[:ascii:][:nonascii:]]*") ?
"\\(.*\n?\\)*" will lead to pathologically slow behavior because it can match in too many different ways. Better use ".*\\(\n.*\\)?"
Actually, I just noticed I can do this with \(.\|[\n]\)*. For example,
[code] $ sudo wpa_supplicant -B -i wlan0 -Dwext -c universitywpa
Successfully initialized wpa_supplicant
ioctl[SIOCSIWENCODEEXT]: Invalid argument
ioctl[SIOCSIWENCODEEXT]: Invalid argument
[/code]
-
(progn
(re-search-forward "[[]code]\\(\\(.\\|[\n]\\)*?\\)[[]/code]" )
(match-string 1))
gives
" $ sudo wpa_supplicant -B -i wlan0 -Dwext -c universitywpa
Successfully initialized wpa_supplicant
ioctl[SIOCSIWENCODEEXT]: Invalid argument
ioctl[SIOCSIWENCODEEXT]: Invalid argument
"
A shorthand for this would be nicer, though, something like
(let ((re-dot-match-all t))
(re-search-forward "[[]code]\\(.*?\\)[[]/code]" )
(match-string 1))
Similar to the case-fold-search use. Or a named character class:
(re-search-forward "[[]code]\\([[:any:]]*?\\)[[]/code]" )
\s- and [:space:] also match newlines, and \ca and [:ascii:] match any ASCII character. But see my answer for a potentially better solution.
Commented
Aug 8, 2015 at 20:45
(search-forward "[code]") (buffer-substring (point) (progn (search-forward "[/code]") (match-beginning 0)))
Commented
Aug 8, 2015 at 23:47
At least in emacs-27, the elsip info page "regexp special" answers the question:
If the lower bound of a range is greater than its upper bound, the range is empty and represents no characters. Thus, ‘[z-a]’ always fails to match, and ‘[^z-a]’ matches any character, including newline.
I tested it a few times, and it seems to work, and this solution is imho more readable and shorter than the other ones.
C-M-.anytime in the minibuffer to toggle whether when you type.in your minibuffer input it matches any char (including newlines) or any char except newlines. This is handy for apropos completion, which uses regexp matching.