# Explain this ruby regex **URL:** \ **Category:** Ruby\ **Created:** [October 3, 2008, 5:40pm UTC](https://www.ruby-forum.com/t/explain-this-ruby-regex/150093 "2008-10-03T17:40:58Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\ **Post date:** [October 3, 2008, 5:40pm UTC](https://www.ruby-forum.com/t/explain-this-ruby-regex/150093/1 "2008-10-03T17:40:58Z")
Can someone explain this regex … “one two”.scan(/\w\*/).length returns 4. I can see it matching the 2 words and the space, what else is it matching on? Is there a null terminator, I thought Ruby strings were not null termed. ---
**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\ **Post date:** [October 3, 2008, 5:46pm UTC](https://www.ruby-forum.com/t/explain-this-ruby-regex/150093/2 "2008-10-03T17:46:14Z")
On Sat, Oct 04, 2008, removed\_email\_address@domain.invalid wrote: > “one two”.scan(/\w\*/).length > > returns 4. I can see it matching the 2 words and the space, what else > is it matching on? Is there a null terminator, I thought Ruby strings > were not null termed. Try replacing #length with #inspect and seeing what the output of scan is. You’ll find that it’s returning two empty strings as well. I suspect what you really want is \w+… Ben ---
**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\ **Post date:** [October 3, 2008, 7:56pm UTC](https://www.ruby-forum.com/t/explain-this-ruby-regex/150093/3 "2008-10-03T19:56:44Z")
On Oct 3, 11:44 am, Ben B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Ben Yeah, you’re right \w+ will pull out the words, which is what I want anyway. Though I’m trying to understand what \w\* is doing. irb(main):015:0\> “one two”.scan(/\w\*/).inspect =\> “["one", "", "two", ""]” My question is, what is the last "", where does it come from. ---
**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\ **Post date:** [October 3, 2008, 8:38pm UTC](https://www.ruby-forum.com/t/explain-this-ruby-regex/150093/4 "2008-10-03T20:38:01Z")
\w\* does not match the space between string “one” and “two”. it matches “one”, \, “two”, \. There are some other examples: ``` irb(main):004:0> "one".scan(/^\w*/) => ["one"] irb(main):005:0> "one".scan(/\w*$/) => ["one", ""] ``` – Patrick ---
**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\ **Post date:** [October 3, 2008, 9:29pm UTC](https://www.ruby-forum.com/t/explain-this-ruby-regex/150093/5 "2008-10-03T21:29:41Z")
The key idea here is that "_" means “match zero or more of” whereas “+” means “match one or more of”. So, when you match \w_ against “one two”, there are zero or more instances of a word character (3, in fact, ‘o’, ‘n’, and ‘e’), so that produces one result. Following that result, there are zero matches of a word character, but since you asked for “zero or more of”, you get that empty string result. Later, rinse, repeat for the “two” part. FWIW, instead of looking at the result with #inspect, I found it more informative to look at the result returned from #scan by itself, e.g. irb\> “one two”.scan(/\w\*/) =\> [“one”, “”, “two”, “”] –wpd ---
**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\ **Post date:** [October 5, 2008, 6:21pm UTC](https://www.ruby-forum.com/t/explain-this-ruby-regex/150093/6 "2008-10-05T18:21:13Z")
On 03.10.2008 18:44, Patrick D. wrote: > The key idea here is that "_" means “match zero or more of” whereas “+” > means “match one or more of”. So, when you match \w_ against “one two”, > there are zero or more instances of a word character (3, in fact, ‘o’, ‘n’, > and ‘e’), so that produces one result. Following that result, there are > zero matches of a word character, but since you asked for “zero or more of”, > you get that empty string result. Later, rinse, repeat for the “two” part. It boils down to this statement: a subexpression with “\*” potentially matches an _empty string anywhere_ in a string. Kind regards robert ---
**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\ **Post date:** [October 3, 2008, 9:47pm UTC](https://www.ruby-forum.com/t/explain-this-ruby-regex/150093/7 "2008-10-03T21:47:42Z")
> FWIW, instead of looking at the result with #inspect, I found it more > informative to look at the result returned from #scan by itself, e.g. > > irb\> “one two”.scan(/\w\*/) > =\> [“one”, “”, “two”, “”] irb displays the expression value using “inspect”, so you are using inspect even though you didn’t ask for it 🙂