# Copying $1.. A loop with two regular expressions

**URL:** <https://www.ruby-forum.com/t/copying-1-a-loop-with-two-regular-expressions/56950>\
**Category:** Ruby\
**Created:** [April 6, 2006, 1:14am UTC](https://www.ruby-forum.com/t/copying-1-a-loop-with-two-regular-expressions/56950 "2006-04-06T01:14:30Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![oky](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/ecae2f/32.png) [@oky](https://www.ruby-forum.com/u/oky)\
**Post date:** [April 6, 2006, 1:14am UTC](https://www.ruby-forum.com/t/copying-1-a-loop-with-two-regular-expressions/56950/1 "2006-04-06T01:14:30Z")

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Hi, sorry if this is a stupid question… i’ve only been programming ruby  
for about six hours.

I’m trying to white a loop to parse through a webpage and get all the  
links to other pages. This loop depends on a regular expression to find  
all the \<a href tags… but inside the loop there is another regular  
expression which looks to see if the link is relative or static. The  
problem is the inner regular expression changes the $1 variable so the  
loop just fails on the first iteration. I’ve tried making a copy of the  
$1 variable but the result just ends up containing nil.

Any help you could offer would be gratefully appreciated

Hears my code so far:

```
	loop do
	 	url = $1
		puts $1 #A url
		puts $url #Always nil ?

 		if $1 =~ /^http/ //Inner regular expression
			new_url = host + path
		else
			new_url = path
		end

		newPage = WebPage.new(new_url, link_depth + 1)

	break unless url =~ @@ahref_filter
	end
```

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<div class="post-metadata">

**Author:** ![oky](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/ecae2f/32.png) [@oky](https://www.ruby-forum.com/u/oky)\
**Post date:** [April 6, 2006, 1:20am UTC](https://www.ruby-forum.com/t/copying-1-a-loop-with-two-regular-expressions/56950/2 "2006-04-06T01:20:58Z")

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Oky wrote:

> Hi, sorry if this is a stupid question… i’ve only been programming ruby  
> for about six hours.
> 
> I’m trying to white a loop to parse through a webpage and get all the  
> links to other pages. This loop depends on a regular expression to find  
> all the \<a href tags… but inside the loop there is another regular  
> expression which looks to see if the link is relative or static. The  
> problem is the inner regular expression changes the $1 variable so the  
> loop just fails on the first iteration. I’ve tried making a copy of the  
> $1 variable but the result just ends up containing nil.

Are you trying to use a command line argument? If so, try ARGV[1]  
instead of $1 (which is a global variable storing the text of the  
first subexpression in the most recent match.

Hal

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<div class="post-metadata">

**Author:** ![oky](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/ecae2f/32.png) [@oky](https://www.ruby-forum.com/u/oky)\
**Post date:** [April 6, 2006, 1:38am UTC](https://www.ruby-forum.com/t/copying-1-a-loop-with-two-regular-expressions/56950/3 "2006-04-06T01:38:53Z")

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Hi Hal,

Thank you for your reply

No i’m not trying to use a command line argument, just use a loop which  
uses two regular expression. After having a fresh look at the code i  
spotted my mistake (url = $1 should have been url = $’) and it seams to  
work now. Although I still don’t understand why I can’t copy the $1  
variable (doller\_one = $1 equals nil?) but it doesn’t matter to much now  
as ruby lets you copy the $’ variable.

Thank very much for taking the time to reply

Oky

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<div class="post-metadata">

**Author:** ![oky](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/ecae2f/32.png) [@oky](https://www.ruby-forum.com/u/oky)\
**Post date:** [April 6, 2006, 1:51am UTC](https://www.ruby-forum.com/t/copying-1-a-loop-with-two-regular-expressions/56950/4 "2006-04-06T01:51:15Z")

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Matthew D. wrote:

> > static. The problem is the inner regular expression changes the $1  
> > puts $1 #A url
> 
> So try changing the “$url” to “url” and see what happens.
> 
> I hope it’s something good.
> 
> Matthew

Huh.

Try “You’ve assigned the value of $1 to the local variable url.”  
That’ll make more sense (maybe).

Sheesh. Sorry. 😉

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<div class="post-metadata">

**Author:** ![oky](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/ecae2f/32.png) [@oky](https://www.ruby-forum.com/u/oky)\
**Post date:** [April 6, 2006, 1:48am UTC](https://www.ruby-forum.com/t/copying-1-a-loop-with-two-regular-expressions/56950/5 "2006-04-06T01:48:09Z")

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Hi there,

Oky wrote:

> Any help you could offer would be gratefully appreciated
> 
> Hears my code so far:
> 
> ```
> loop do
> url = $1
> puts $1 #A url
> puts $url #Always nil ?
> 
> ```

Here’s _a_ problem for you to start with. You’ve assigned the value of  
1 to the local variable url. When you puts $url, you are examining and  
printing the global variable $url. Since you haven’t assigned anything  
to $url yet, it is nil.

In Ruby an unadorned name like “url” is either a local variable or  
method call. Putting a “$” on the front of something tells Ruby that  
you want to refer to a global.

So try changing the “$url” to “url” and see what happens.

I hope it’s something good.

Matthew

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<div class="post-metadata">

**Author:** ![oky](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/ecae2f/32.png) [@oky](https://www.ruby-forum.com/u/oky)\
**Post date:** [April 6, 2006, 2:09am UTC](https://www.ruby-forum.com/t/copying-1-a-loop-with-two-regular-expressions/56950/6 "2006-04-06T02:09:21Z")

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Oky wrote:

> Thanks Matthew,
> 
> Your absolutely right. A schoolboy mistake from me :S I come from a  
> C++/Asm background and havenâ??t got the hang of all these undefined  
> variables yet.
> 
> Thanks again for your reply

No problem! I’m glad that I could help.

Have fun!

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<div class="post-metadata">

**Author:** ![oky](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/ecae2f/32.png) [@oky](https://www.ruby-forum.com/u/oky)\
**Post date:** [April 6, 2006, 2:01am UTC](https://www.ruby-forum.com/t/copying-1-a-loop-with-two-regular-expressions/56950/7 "2006-04-06T02:01:59Z")

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Thanks Matthew,

Your absolutely right. A schoolboy mistake from me :S I come from a  
C++/Asm background and havenâ??t got the hang of all these undefined  
variables yet.

Thanks again for your reply