# Newbie: how to find & extract a string from a file

**URL:** <https://www.ruby-forum.com/t/newbie-how-to-find-extract-a-string-from-a-file/70548>\
**Category:** Ruby\
**Created:** [September 30, 2006, 12:46am UTC](https://www.ruby-forum.com/t/newbie-how-to-find-extract-a-string-from-a-file/70548 "2006-09-30T00:46:06Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Esmail\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/e0b2c6/32.png) [@Esmail\_B](https://www.ruby-forum.com/u/Esmail_B)\
**Post date:** [September 30, 2006, 12:46am UTC](https://www.ruby-forum.com/t/newbie-how-to-find-extract-a-string-from-a-file/70548/1 "2006-09-30T00:46:06Z")

</div>

Hi,

Just starting out to explore Ruby (I like it) and I have  
a question.

I have an HTML file that contains several references to jpg files.

I would like to extract the filename with the .jpg extension.  
What is the best approach for this?

It appears each .jpg reference is on its own line.

Thanks!

Esmail

---

<div class="post-metadata">

**Author:** ![Esmail\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/e0b2c6/32.png) [@Esmail\_B](https://www.ruby-forum.com/u/Esmail_B)\
**Post date:** [September 30, 2006, 2:12am UTC](https://www.ruby-forum.com/t/newbie-how-to-find-extract-a-string-from-a-file/70548/2 "2006-09-30T02:12:51Z")

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I’m sure someone will have a better way of doing this… but…  
Assuming it has ![](https://www.ruby-forum.com/something.jpg)

## 

imgs = []  
IO.readlines(“c:/somefile.html”).each {|line| imgs \<\< line.split("\<img  
src="")[1].to\_s.split(""")[0] if line.match("\<img src=") }  
puts imgs.join("\n")

##

---

<div class="post-metadata">

**Author:** ![Esmail\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/e0b2c6/32.png) [@Esmail\_B](https://www.ruby-forum.com/u/Esmail_B)\
**Post date:** [September 30, 2006, 2:50am UTC](https://www.ruby-forum.com/t/newbie-how-to-find-extract-a-string-from-a-file/70548/3 "2006-09-30T02:50:53Z")

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Esmail B. wrote:

> I would like to extract the filename with the .jpg extension.  
> What is the best approach for this?

Hi there,

You could use raw regexps and do it yourself, but you should probably  
use an HTML parser to extract HTML data. 😉

A nice HTML parser is Hpricot [1], but it requires an extension (you  
cen get it very easily via gems, see the link below). It is very easy  
to use, and it’s fast.

Using Hpricot, you can do something like this:

require ‘hpricot’  
require ‘open-uri’  
soc = open(‘[http://utopia.utexas.edu/maps/ireland.html](http://utopia.utexas.edu/maps/ireland.html)’)  
doc = Hpricot(soc)  
soc.close  
doc.search(‘//a’).each { |elem|  
href = elem.attributes[‘href’]  
if not href.nil? and  
[‘.jpg’, ‘.jpeg’].include?(File.extname(href))  
puts href  
end  
}

Note that you can also use the built-in REXML parser [2], and do  
something like:

require ‘rexml/document’  
require ‘open-uri’  
include REXML  
soc = open(‘[http://utopia.utexas.edu/maps/ireland.html](http://utopia.utexas.edu/maps/ireland.html)’)  
doc = Document.new(soc)  
soc.close  
doc.elements.each(‘//a’) { |elem|  
href = elem.attributes[‘href’]  
if not href.nil? and  
[‘.jpg’, ‘.jpeg’].include?(File.extname(href))  
puts href  
end  
}

[1] [http://code.whytheluckystiff.net/hpricot/](http://code.whytheluckystiff.net/hpricot/)  
[2] [http://www.germane-software.com/software/rexml/docs/tutorial.html](http://www.germane-software.com/software/rexml/docs/tutorial.html)

Regards,  
Jordan

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<div class="post-metadata">

**Author:** ![Esmail\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/e0b2c6/32.png) [@Esmail\_B](https://www.ruby-forum.com/u/Esmail_B)\
**Post date:** [September 30, 2006, 4:40am UTC](https://www.ruby-forum.com/t/newbie-how-to-find-extract-a-string-from-a-file/70548/4 "2006-09-30T04:40:58Z")

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x1 wrote:

> I’m sure someone will have a better way of doing this… but…  
> Assuming it has ![](https://www.ruby-forum.com/something.jpg)
> 
> ## 
> 
> imgs = []  
> IO.readlines(“c:/somefile.html”).each {|line| imgs \<\< line.split("\<img  
> src="")[1].to\_s.split(""")[0] if line.match("\<img src=") }  
> puts imgs.join("\n")
> 
> ##

Hi,

thanks … this will get me started. I feel like I could do this  
using various unix tools (grep/awk), but I’m trying to learn  
Ruby …

Esmail

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<div class="post-metadata">

**Author:** ![Esmail\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/e0b2c6/32.png) [@Esmail\_B](https://www.ruby-forum.com/u/Esmail_B)\
**Post date:** [September 30, 2006, 4:46am UTC](https://www.ruby-forum.com/t/newbie-how-to-find-extract-a-string-from-a-file/70548/5 "2006-09-30T04:46:59Z")

</div>

Hi,

Thank you so much for these pointers. Am I correct in assuming  
that REXML comes as part of standard Ruby? If so I think I will  
go that route first.

I could cobble something together using various Linux tools  
(grep and awk come to mind), but I want something in Ruby  
(because I want to learn it) and also because it will be  
more portable, for instance to the XP platform.

I appreciate you taking the time to post this and the references.  
If you have any other ideas/approaches, I’m game.

Thanks again,

Esmail

---

<div class="post-metadata">

**Author:** ![Esmail\_B](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/e0b2c6/32.png) [@Esmail\_B](https://www.ruby-forum.com/u/Esmail_B)\
**Post date:** [September 30, 2006, 7:21am UTC](https://www.ruby-forum.com/t/newbie-how-to-find-extract-a-string-from-a-file/70548/6 "2006-09-30T07:21:49Z")

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Esmail B. wrote:

> Thank you so much for these pointers. Am I correct in assuming  
> that REXML comes as part of standard Ruby? If so I think I will  
> go that route first.

Glad to help. And yes, REXML is a pure-ruby parser (uses regexp under  
the hood) and is included with ruby stdlib since 1.8.

> I could cobble something together using various Linux tools  
> (grep and awk come to mind), but I want something in Ruby  
> (because I want to learn it) and also because it will be  
> more portable, for instance to the XP platform.

REXML is more portible, albeit not as fast as Hpricot, which is  
implemented as a compiled C extension for ruby.

Have fun learning ruby! It’s a nice language. 🙂

Regards,  
Jordan