# Newbie regex question about \\w

**URL:** <https://www.ruby-forum.com/t/newbie-regex-question-about-w/52482>\
**Category:** Ruby\
**Created:** [January 14, 2006, 11:14pm UTC](https://www.ruby-forum.com/t/newbie-regex-question-about-w/52482 "2006-01-14T23:14:31Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![jeff](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e19b73/32.png) [@jeff](https://www.ruby-forum.com/u/jeff)\
**Post date:** [January 14, 2006, 11:14pm UTC](https://www.ruby-forum.com/t/newbie-regex-question-about-w/52482/1 "2006-01-14T23:14:31Z")

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I’m trying to parse ruby files to find all the class definitions in the  
file. For each line in the file, I thought I could use the following to  
pull out the class name:

\bclass\b(\w+)\b

so then $1 would give me the class name.

But it doesn’t work:

irb(main):001:0\> line = “class Article \< MyBaseClass”  
=\> “class Article \< ActiveRecord::Base”  
irb(main):002:0\> line =~ /\bclass\b(\w+)\b/  
=\> nil

I think I narrowed down the problem to my use of \w, but I can’t  
understand why.

For extra credit, anybody know how I can make sure I can ignore comments  
and quoted strings? I want to make sure I ignore these things:

if option\_exists # handle class options

as well as

puts “Your are in a class by yourself”

But those are advanced… if I can just get the first one working I’ll  
be grateful!

Thanks,  
Jeff

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**Author:** ![jeff](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e19b73/32.png) [@jeff](https://www.ruby-forum.com/u/jeff)\
**Post date:** [January 14, 2006, 11:22pm UTC](https://www.ruby-forum.com/t/newbie-regex-question-about-w/52482/2 "2006-01-14T23:22:25Z")

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On Jan 14, 2006, at 4:14 PM, Jeff C. wrote:

> I’m trying to parse ruby files to find all the class definitions in  
> the  
> file. For each line in the file, I thought I could use the  
> following to  
> pull out the class name:
> 
> \bclass\b(\w+)\b
> 
> so then $1 would give me the class name.

You’re close, you just forgot to allow for some space between class  
and the name. A boundary is a zero-width assertion, so it’s not enough:

\bclass\s+(\w+)\b

Hope that helps.

James Edward G. II

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**Author:** ![jeff](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e19b73/32.png) [@jeff](https://www.ruby-forum.com/u/jeff)\
**Post date:** [January 14, 2006, 11:25pm UTC](https://www.ruby-forum.com/t/newbie-regex-question-about-w/52482/3 "2006-01-14T23:25:10Z")

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James G. wrote:

> You’re close, you just forgot to allow for some space between class  
> and the name. A boundary is a zero-width assertion, so it’s not enough:

Awesome. Thanks a lot.

Jeff

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**Author:** ![jeff](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e19b73/32.png) [@jeff](https://www.ruby-forum.com/u/jeff)\
**Post date:** [January 14, 2006, 11:34pm UTC](https://www.ruby-forum.com/t/newbie-regex-question-about-w/52482/4 "2006-01-14T23:34:30Z")

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On Jan 14, 2006, at 5:14 PM, Jeff C. wrote:

> But it doesn’t work:  
> comments
> 
> Thanks,  
> Jeff
> 
> –  
> Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/).

your \w is right. \b doesn’t work the way you think it does though.  
It doesn’t consume anything, ie;

"\<-- \b is just before the ‘c’  
c  
l  
a  
s  
s\_\_ \b is in between the ‘s’ and the space  
 ← space doesn’t match \w  
A  
r  
t  
i  
c  
l  
e  
.  
.  
.

So what you really want is  
line =~ /\bclass\s+(\w+)/  
irb(main):007:0\> line =~ /\bclass\s+(\w+)/  
=\> 0  
irb(main):008:0\> $1  
=\> “Article”

As for the other questions, comments aren’t SO hard:

/#.\*$/ unless of course you want to handle strings, then you have to  
worry about # inside of strings. I’m not even going to begin to try  
to create a regex to match quoted strings, thats all sorts of  
difficult especially with heredocs and such. I would take a look at  
rdoc and see if you can’t manipulate it to get a list of classes for  
you.

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**Author:** ![jeff](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e19b73/32.png) [@jeff](https://www.ruby-forum.com/u/jeff)\
**Post date:** [January 14, 2006, 11:49pm UTC](https://www.ruby-forum.com/t/newbie-regex-question-about-w/52482/5 "2006-01-14T23:49:33Z")

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Hi –

On Sun, 15 Jan 2006, Jeff C. wrote:

> be grateful!  
> You might try this:

/^\s\*class\s+(\w+)/

which will only match “class …” at the beginning of a line or with  
only spaces to its left. It’s certainly not impossible to get false  
positives or negatives this way, but in the normal course of a  
normally-written Ruby program file it should be close to 100%.

Don’t forget, though, that you might get “::” in a class name, like  
this:

module M  
end

class M::C  
end

and just going for \w+ will give you the module name, not the class  
name.

David

–  
David A. Black  
removed\_email\_address@domain.invalid

“Ruby for Rails”, from Manning Publications, coming April 2006!

> **[Ruby for Rails](https://www.manning.com/books/ruby-for-rails)**
>
> NEWER EDITION AVAILABLE
> 
> The Well-Grounded Rubyist, Second Edition is now available. An eBook of the previous edition, The Well-Grounded Rubyist is included at no additional cost when you buy the revised edition! 
> 
> 
> Ruby for Rails helps Rails...

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**Author:** ![jeff](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e19b73/32.png) [@jeff](https://www.ruby-forum.com/u/jeff)\
**Post date:** [January 14, 2006, 11:49pm UTC](https://www.ruby-forum.com/t/newbie-regex-question-about-w/52482/6 "2006-01-14T23:49:35Z")

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> […]  
> especially with heredocs and such. I would take a look at rdoc and see  
> if you can’t manipulate it to get a list of classes for you.

Maybe this is about regexps and i’m totaly off, but what about:

* * *

before = Object.constants  
require ‘sqlite3’ # put your file here  
after = Object.constants

## p(after - before)

output:

[“NKF”, “Deprecated”, “SQLite3”, “Base64”, “Kconv”, “ParseDate”]

cheers

Simon

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<div class="post-metadata">

**Author:** ![jeff](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e19b73/32.png) [@jeff](https://www.ruby-forum.com/u/jeff)\
**Post date:** [January 15, 2006, 12:13am UTC](https://www.ruby-forum.com/t/newbie-regex-question-about-w/52482/7 "2006-01-15T00:13:44Z")

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On Jan 14, 2006, at 5:49 PM, Simon Kröger wrote:

> Simon

Clever!

before = Object.constants  
require ‘file’  
after = Object.constants  
files\_classes = (after - before).select { |x| Class ===  
Object.const\_get(x) }