# Regex woes with breaklines

**URL:** <https://www.ruby-forum.com/t/regex-woes-with-breaklines/165190>\
**Category:** Ruby\
**Created:** [April 10, 2009, 1:02am UTC](https://www.ruby-forum.com/t/regex-woes-with-breaklines/165190 "2009-04-10T01:02:38Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![aawilson](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/e495f1/32.png) [@aawilson](https://www.ruby-forum.com/u/aawilson)\
**Post date:** [April 10, 2009, 1:02am UTC](https://www.ruby-forum.com/t/regex-woes-with-breaklines/165190/1 "2009-04-10T01:02:38Z")

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Hello, all. I’ve been banging my head against this for a little bit,  
and I’m no closer to a solution. The issue is that I have a string  
where I would like to gsub all line ends (’\n’ or ‘\r\n’) into ‘  
’,  
while preserving the line ends. The catch is that I don’t want to gsub  
anything that looks like ‘  
\r\n’ or ‘  
\n’, to prevent my gsub  
from inserting breaklines on subsequent edits of this string. I’ve  
tried gsub with the regex /(?!\<br\s\*/\>)($)[^\z]/, but haven’t had any  
luck getting it to match. For example, on the string  
“test\r\ntest  
\r\ntest”, it will match both of the ‘\r\n’ sets,  
instead of only the first one (which would be optimal).

Thanks in advance for your time.

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**Author:** ![aawilson](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/e495f1/32.png) [@aawilson](https://www.ruby-forum.com/u/aawilson)\
**Post date:** [April 10, 2009, 9:06am UTC](https://www.ruby-forum.com/t/regex-woes-with-breaklines/165190/2 "2009-04-10T09:06:08Z")

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On Fri, Apr 10, 2009 at 1:03 AM, Aa Wilson [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Thanks in advance for your time.

Replace the   
 along with the new line  
Also remember that a new line can be CR (Mac), LF (Linux) or CRLF  
(Windows)

s = “test\r\ntest  
\r\ntest\ntest\rtest  
\ntest”  
s.gsub(/(?:\<br _/_\>)\*(?:\r\n|\n|\r)/, “  
\n”)  
#=\> “test  
\ntest  
\ntest  
\ntest  
\ntest  
\ntest”

Andrew T.  
[http://ramblingsonrails.com](http://ramblingsonrails.com)  
[http://www.linkedin.com/in/andrewtimberlake](http://www.linkedin.com/in/andrewtimberlake)

“I have never let my schooling interfere with my education” - Mark Twain

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**Author:** ![aawilson](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/e495f1/32.png) [@aawilson](https://www.ruby-forum.com/u/aawilson)\
**Post date:** [April 10, 2009, 2:51pm UTC](https://www.ruby-forum.com/t/regex-woes-with-breaklines/165190/3 "2009-04-10T14:51:54Z")

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Andrew T. wrote:

> s = “test\r\ntest  
> \r\ntest\ntest\rtest  
> \ntest”  
> s.gsub(/(?:\<br _/_\>)\*(?:\r\n|\n|\r)/, “  
> \n”)  
> #=\> “test  
> \ntest  
> \ntest  
> \ntest  
> \ntest  
> \ntest”

Thanks a million. It feels like a waste replacing something that’s  
already there, but I suppose that’s just my conceptions of real life  
getting in the way of my abstractions.

I was actually hoping that ‘$’ (or possibly ‘$$?’) would cover all the  
CR/LF/CRLF cases for me, was I mistaken about that?

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**Author:** ![aawilson](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/e495f1/32.png) [@aawilson](https://www.ruby-forum.com/u/aawilson)\
**Post date:** [April 10, 2009, 11:47pm UTC](https://www.ruby-forum.com/t/regex-woes-with-breaklines/165190/4 "2009-04-10T23:47:53Z")

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On 10.04.2009 14:52, Aa Wilson wrote:

> Andrew T. wrote:
> 
> > s = “test\r\ntest  
> > \r\ntest\ntest\rtest  
> > \ntest”  
> > s.gsub(/(?:\<br _/_\>)\*(?:\r\n|\n|\r)/, “  
> > \n”)  
> > #=\> “test  
> > \ntest  
> > \ntest  
> > \ntest  
> > \ntest  
> > \ntest”
> 
> Thanks a million. It feels like a waste replacing something that’s  
> already there, but I suppose that’s just my conceptions of real life  
> getting in the way of my abstractions.

Not necessarily: with 1.9’s regular expression engine there is negative  
lookbehind as well. You could use that to prevent substitution of  
newlines which are preceeded by a   
 already.

[http://www.geocities.jp/kosako3/oniguruma/doc/RE.txt](http://www.geocities.jp/kosako3/oniguruma/doc/RE.txt)

> I was actually hoping that ‘$’ (or possibly ‘$$?’) would cover all the  
> CR/LF/CRLF cases for me, was I mistaken about that?

I believe it does not cover \r alone. In every case it is safer to be  
explicit IMHO. Btw, I believe you can simplify to (?:\r\n?|\n).

Kind regards

robert