# Oniguruma question

**URL:** <https://www.ruby-forum.com/t/oniguruma-question/148035>\
**Category:** Ruby\
**Created:** [September 8, 2008, 3:25pm UTC](https://www.ruby-forum.com/t/oniguruma-question/148035 "2008-09-08T15:25:29Z")\
**Posts on this page:** 8\
**Page:** 1

<div class="post-metadata">

**Author:** ![Kenneth\_McDonald](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/dc4da7/32.png) [@Kenneth\_McDonald](https://www.ruby-forum.com/u/Kenneth_McDonald)\
**Post date:** [September 8, 2008, 3:25pm UTC](https://www.ruby-forum.com/t/oniguruma-question/148035/1 "2008-09-08T15:25:29Z")

</div>

For those adventurous souls who are already using Oniguruma…

With the following Oniguruma re:

print “aabb”.index(/.+?(?\<!a)/)  
print “\n”

My reasoning tells me I should be getting 3, but I’m getting 0.  
Basically, the .+ should force the re ‘cursor’ past at least the first  
a; after that, the negative lookback should force it past the first b.  
Could someone explain where I’m misunderstanding?

Thanks,  
Ken

---

<div class="post-metadata">

**Author:** ![Kenneth\_McDonald](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/dc4da7/32.png) [@Kenneth\_McDonald](https://www.ruby-forum.com/u/Kenneth_McDonald)\
**Post date:** [September 8, 2008, 5:30pm UTC](https://www.ruby-forum.com/t/oniguruma-question/148035/2 "2008-09-08T17:30:56Z")

</div>

2008/9/8 Kenneth McDonald [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> explain where I’m misunderstanding?  
> Your reasoning about “.+” is wrong. Non greedy matching does only mean  
> that the /end point/ of a match might be moved to the left, but never  
> the /start point/ be moved to the right. So .+ matches directly at  
> the beginning of the string.

Any practical problem that you’re trying to solve (and we can try to  
tackle)? 🙂

Kind regards

robert

---

<div class="post-metadata">

**Author:** ![Kenneth\_McDonald](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/dc4da7/32.png) [@Kenneth\_McDonald](https://www.ruby-forum.com/u/Kenneth_McDonald)\
**Post date:** [September 8, 2008, 7:46pm UTC](https://www.ruby-forum.com/t/oniguruma-question/148035/3 "2008-09-08T19:46:19Z")

</div>

I’m writing a library to make re’s easier to use 🙂 This is in the  
test suite.

Thanks for the feedback, that comes as a real surprise to me. So maybe  
I’ll try /…+?/

Cheers,  
Ken

---

<div class="post-metadata">

**Author:** ![Kenneth\_McDonald](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/dc4da7/32.png) [@Kenneth\_McDonald](https://www.ruby-forum.com/u/Kenneth_McDonald)\
**Post date:** [September 9, 2008, 4:52am UTC](https://www.ruby-forum.com/t/oniguruma-question/148035/4 "2008-09-09T04:52:40Z")

</div>

On Mon, Sep 08, 2008 at 10:18:01PM +0900, Kenneth McDonald wrote:

> Could someone explain where I’m misunderstanding?  
> Not exactly an answer, but . . .

Why use two print statements, the second just to add a newline  
character,  
rather than using puts?

---

<div class="post-metadata">

**Author:** ![Kenneth\_McDonald](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/dc4da7/32.png) [@Kenneth\_McDonald](https://www.ruby-forum.com/u/Kenneth_McDonald)\
**Post date:** [September 9, 2008, 5:06am UTC](https://www.ruby-forum.com/t/oniguruma-question/148035/5 "2008-09-09T05:06:41Z")

</div>

'Cause I’m a Ruby newbie who’s still learning this stuff 🙂

Ken

---

<div class="post-metadata">

**Author:** ![Kenneth\_McDonald](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/dc4da7/32.png) [@Kenneth\_McDonald](https://www.ruby-forum.com/u/Kenneth_McDonald)\
**Post date:** [September 9, 2008, 6:03am UTC](https://www.ruby-forum.com/t/oniguruma-question/148035/6 "2008-09-09T06:03:26Z")

</div>

On Tue, Sep 09, 2008 at 11:30:56AM +0900, Kenneth McDonald wrote:

> 'Cause I’m a Ruby newbie who’s still learning this stuff 🙂

Ah! I understand.

In that case, take that as a suggestion instead of a question:

“You can clean up that code a little by using puts instead of print.”

Something like that.

Also, I think it’s generally considered preferable on this list to avoid  
TOFU[1] posting. I’m still not 100% sure how strict or official such a  
rule is on ruby-talk, though.

[1]: TOFU = Text Over, Fullquote Under; also known sometimes as “top  
posting”, without trimming quoted text

---

<div class="post-metadata">

**Author:** ![Kenneth\_McDonald](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/dc4da7/32.png) [@Kenneth\_McDonald](https://www.ruby-forum.com/u/Kenneth_McDonald)\
**Post date:** [September 9, 2008, 5:42pm UTC](https://www.ruby-forum.com/t/oniguruma-question/148035/7 "2008-09-09T17:42:58Z")

</div>

It was part of a unit testing suite. I did figure out where I was  
going wrong, a silly mistake on my part which I should’ve been past  
years ago. Thanks for the help.

Ken

---

<div class="post-metadata">

**Author:** ![Kenneth\_McDonald](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/dc4da7/32.png) [@Kenneth\_McDonald](https://www.ruby-forum.com/u/Kenneth_McDonald)\
**Post date:** [September 9, 2008, 8:30am UTC](https://www.ruby-forum.com/t/oniguruma-question/148035/8 "2008-09-09T08:30:55Z")

</div>

On 08.09.2008 19:38, Kenneth McDonald wrote:

> I’m writing a library to make re’s easier to use 🙂 This is in the  
> test suite.
> 
> Thanks for the feedback, that comes as a real surprise to me. So maybe  
> I’ll try /…+?/

This one won’t match after “aa”. Instead it will match “aa”. I do not  
know what you intend to match so I cannot really comment. This is  
clearly a toy example, isn’t it? There are multiple ways to match “bb”  
in “aabb” and it is completely unclear to me what you are after.

Your original RX literally translated means “match anything which is not  
preceded by a” which is especially true for every character at the  
beginning of a string.

Btw, I can recommend “Mastering Regular Expressions” - it is a really  
good book on the matter.

Kind regards

robert