This Ruby code raises an error if the XPath query fails because the attribute being queried did not exist for the given element.

  def map_pattr(node, fieldx, valuex)
    begin
    parameter = node.root.elements["parameter[@field='#{fieldx}']"]
    parameter.add_attribute('value', valuex)
    parameter
    
    rescue
      puts 'feedpopulated.rb: map_attr() the field ' + fieldx + ' was not found in params.'
      raise
    end
  end

Notice that a raise statement is used to ensure that the system error message is raised and any further code execution is halted.

Without adding a customized helpful message I would be left scratching my head trying to work out what the following system error message meant.

./feedpopulated.rb:27:in `map_pattr': undefined method `add_attribute' for nil:NilClass (NoMethodError)
     from ./feedpopulated.rb:51:in `create_record'
     from ./feedpopulated.rb:49:in `each'
     from ./feedpopulated.rb:49:in `create_record'
     from ./recordx.rb:91:in `call_create'
     from ./s3fileuploader_handler.rb:14:in `call'
     from ./s3fileuploader_handler.rb:40:in `invoke'
     from ./uploadtwitteraudio.rb:22:in `initialize'
     from /usr/lib/ruby/1.8/rexml/element.rb:890:in `each'
     from /usr/lib/ruby/1.8/rexml/xpath.rb:53:in `each'
     from /usr/lib/ruby/1.8/rexml/element.rb:890:in `each'
     from ./uploadtwitteraudio.rb:18:in `initialize'
     from ./uploadtwitteraudio.rb:72:in `new'
     from ./uploadtwitteraudio.rb:72

Reference: Programming Ruby: The Pragmatic Programmer's Guide - Exceptions, Catch, and Throw [ruby-doc.org]

A few XPath examples copied from XPath Syntax [w3schools.com]

Predicates

/bookstore/book[1] 	# Selects the first book element that is the child of the bookstore element. 
                        # Note: IE5 and later has implemented that [0] should be the first node, 
                        # but according to the W3C standard it should have been [1]!!
/bookstore/book[last()] 	# Selects the last book element that is the child of the bookstore element
/bookstore/book[last()-1] 	# Selects the last but one book element that is the child of the bookstore element
/bookstore/book[position()<3] 	# Selects the first two book elements that are children of the bookstore element
//title[@lang] 	# Selects all the title elements that have an attribute named lang

Selecting Unknown Nodes

/bookstore/* 	# Selects all the child nodes of the bookstore element
//* 	# Selects all elements in the document
//title[@*] 	# Selects all title elements which have any attribute

Selecting Several Paths

//book/title | //book/price  	# Selects all the title AND price elements of all book elements

1) Log into an irb session, and enter your S3 login details.

require 'rubygems'
require 'aws/s3'

  AWS::S3::Base.establish_connection!(
    :access_key_id     => 'REPLACE_ME',
    :secret_access_key => 'REPLACE_ME'
  )

output:
=> #<AWS::S3::Connection:0xb75e0594 @http=#<Net::HTTP s3.amazonaws.com:80 open=false>, @secret_access_key="", @options={:server=>"s3.amazonaws.com", :access_key_id=>"", :port=>80, :secret_access_key=>"", :persistent=>true}, @access_key_id="19S45GYAGWK8DC2B8VG2">

2) Browse the existing buckets.

AWS::S3::Service.buckets

output:
=> [#<AWS::S3::Bucket:0xb75cc850 @object_cache=[], @attributes={"name"=>"ogg.twitteraudio.com", "creation_date"=>Sat Apr 26 10:40:16 UTC 2008}>, #<AWS::S3::Bucket:0xb75cc83c @object_cache=[], @attributes={"name"=>"t1000", "creation_date"=>Fri Apr 25 21:35:21 UTC 2008}>, #<AWS::S3::Bucket:0xb75cc814 @object_cache=[], @attributes={"name"=>"t2000", "creation_date"=>Fri Apr 25 21:53:15 UTC 2008}>]

3) Browse the buckets in a programmatical way.

AWS::S3::Service.buckets.each {|b| puts b.name}

output:
ogg.twitteraudio.com
t1000
t2000


4) Add a new bucket called t3000.

AWS::S3::Bucket.create('t3000')

output:
=> true

5) Observe adding the bucket again doesn't cause an error.

AWS::S3::Bucket.create('t3000')

output:
=> true

6) View the buckets again.

AWS::S3::Service.buckets

output:
=> [#<AWS::S3::Bucket:0xb75cc850 @object_cache=[], @attributes={"name"=>"ogg.twitteraudio.com", "creation_date"=>Sat Apr 26 10:40:16 UTC 2008}>, #<AWS::S3::Bucket:0xb75cc83c @object_cache=[], @attributes={"name"=>"t1000", "creation_date"=>Fri Apr 25 21:35:21 UTC 2008}>, #<AWS::S3::Bucket:0xb75cc814 @object_cache=[], @attributes={"name"=>"t2000", "creation_date"=>Fri Apr 25 21:53:15 UTC 2008}>]

Note: You would expect t3000 to be in there however it didn't appear possibly because of the bucket permissions.

7) Let's then look for bucket t3000.

t3000 = AWS::S3::Bucket.find('t3000')

output:
=> #<AWS::S3::Bucket:0xb76df724 @object_cache=[], @attributes={"prefix"=>nil, "name"=>"t3000", "marker"=>nil, "max_keys"=>1000, "is_truncated"=>false, "xmlns"=>"http://s3.amazonaws.com/doc/2006-03-01/"}>

8) Now that we've found the bucket let's upload a text file called works.txt.

file = "works.txt"

output:
=> "works.txt"

AWS::S3::S3Object.store(file, open(file), 't3000', :access => :public_read)

output:
=> #<AWS::S3::S3Object::Response:0x-608926458 200 OK>

9) Setting the file access to :public_read allows us to view the file from the http location http://t3000.s3.amazonaws.com/works.txt

References:
http://amazon.rubyforge.org/
upload_to_s3 - Ruby S3 upload client [dzone.com]

*update: 14:30 30 April 2008 *
I didn't use Bucket.objects(:reload) which is the reason why the bucket t3000 didn't show up with the statement Service.buckets

Reference: spatten design - Amazon S3, Ruby and Rails slides [spattendesign.com]

This ruby code builds upon the code S3 upload client for Ruby [dzone.com] by reading the account details and file details from XML files.

#!/usr/bin/env ruby
#file : rubys3file2upload.rb

require 'rubygems'
require 'aws/s3'
require 'rexml/document'
include REXML

class S3FileUpload

  def initialize(xml_accounts_file, xml_upload_file)
    initialize_account(xml_accounts_file)
    main(xml_upload_file)
  end

  def initialize_account(accounts_file)

    file = File.new(accounts_file)
    doc = Document.new(file)

    account = doc.root.elements['records/access']
    h = Hash.new
    h[:access_key_id] = account.elements['key_id'].text.to_s
    h[:secret_access_key] = account.elements['secret'].text.to_s
    AWS::S3::Base.establish_connection!(h)

  end

  def main(xml_upload_file)
    file = File.new(xml_upload_file)
    doc = Document.new(file)
puts doc
    doc.root.elements.each('records/file') do |f|
      local_file = f.elements['local'].text.to_s
      bucket = f.elements['bucket'].text.to_s
      mime_type = f.elements['mime_type'].text.to_s
      upload(local_file, mime_type, bucket)
    end
  end

  def upload(local_file, mime_type, bucket)

    base_name = File.basename(local_file)

    puts "Uploading #{local_file} as '#{base_name}' to '#{bucket}'"

    AWS::S3::S3Object.store(
      base_name,
      File.open(local_file),
      bucket,
      :content_type => mime_type,
      :access => :public_read
    )

    puts "Uploaded!"
  end

end

if __FILE__ == $0
  s3fu = S3FileUpload.new('s3accounts.xml', 's3files2upload.xml')
end

file: s3accounts.xml

<s3accounts>
  <summary/>
  <records>
    <access id="100"><name>REPLACE_ME</name><key_id>REPLACE_ME</key_id><secret>REPLACE_ME</secret></access>
  </records>
</s3accounts>

file: s3files2upload.xml

<s3files2upload>
  <summary/>
  <records>
    <file>
      <local>autocomplete.html</local>
      <bucket>t2000</bucket>
      <mime_type>text/html</mime_type>
    </file>
    <file>
      <local>autocomplete2.html</local>
      <bucket>t2000</bucket>
      <mime_type>text/html</mime_type>
    </file>
    <file>
      <local>autocomplete3.html</local>
      <bucket>t2000</bucket>
      <mime_type>text/html</mime_type>
    </file>
  </records>
</s3files2upload>

Note: The file given the correct permission could be read from http://t2000.s3.amazonaws.com/autocomplete.html

Reference: http://amazon.rubyforge.org/

#!/usr/bin/ruby

require 'cgi'

cgi = CGI.new
print cgi.header({'Status' => '302 Moved', 'location' =>  'http://www.wired.com'})

or

url = 'http://www.wired.com/'
print cgi.header({'status'=>'REDIRECT', 'Location'=>url})

References:
RE: cgi redirect [nagaokaut.ac.jp]
Ruby/CGI - assari [mokehehe.com]
HTTP/1.1: Status Code Definitions [w3.org]

source: Using Internal & External Scripts, [rit.edu]

<script type="text/ecmascript" xlink:href="scripts/changeCircle.js"/>

This ECMAScript extracts the filename from a URL. eg. the filename 'index4.svg' would be extracted from the document.URL with the value 'http://rorbuilder.info/r/whiteboardqueue/index4.svg'.

var regexp = /(\w|[-.])+$/
str = document.URL
a = regexp.exec(str)
alert(a[0])

Reference: Regular Expressions: Methods - Doc JavaScript [webreference.com]

To reference a CSS file within an SVG file refer to the following example code.

<?xml-stylesheet href="styles_austria_1.css" type="text/css"?> 

Here's what an SVG CSS file looks like.

.str1 {stroke:#0093DD;stroke-width:16;color:#0093DD}
.str2 {stroke:#0093DD;stroke-width:12}
.str3 {stroke:#0093DD;stroke-width:10}
.str4 {stroke:#0093DD;stroke-width:6}

.str0 {stroke:#DA251D;stroke-width:55;color:#DA251D}
.str6 {stroke:#BB90BB;stroke-width:44;color:#BB90BB}
.str5 {stroke:#0093DD;stroke-width:4}
.str7 {stroke:#1F1A17;stroke-width:13}

.fil0 {fill:none}
.fil2 {fill:#1F1A17}
.fil1 {fill:#C4E5FA}
.fil3 {fill:#FFFFFF}

Source: Example for using CSS-Styles [carto.net]
Reference: Styling - SVG 1.1 - 20030114 [w3.org]

First of all the Ruby code reads the text, splits it into an array and then saves it in XML format.

require 'rexml/document'
include REXML

a = "Open source is a development method for software that harnesses the power of distributed peer 
review and transparency of process. The promise of open source is better quality, higher reliability, 
more flexibility, lower cost, and an end to predatory vendor lock-in.".split(' ') 

doc = Document.new
doc.add_element('text')
oline = Element.new('line')

char_count = 0
a.each do |word|
  
  oword = Element.new('word')
  oword.text = word.to_s
  oword.add_attribute('length',char_count)
  oline << oword 
  char_count += word.length
  
  if char_count > 50
    doc.root << oline
    oline = Element.new('line')
    char_count = 0
  end
end
doc.root << oline
puts char_count
puts doc

Here's a sample of the XML created

<text>
  <line>
    <word length='0'>Open</word><word length='4'>source</word><word length='10'>is</word>
    <word length='12'>a</word><word length='13'>development</word><word length='24'>method</word>
    <word length='30'>for</word><word length='33'>software</word><word length='41'>that</word>
    <word length='45'>harnesses</word>
  </line>
  <line>
    <word length='0'>the</word><word length='3'>power</word>
    <word length='8'>of</word><word length='10'>distributed</word><word length='21'>peer</word>
    <word length='25'>review</word><word length='31'>and</word><word length='34'>transparency</word>
    <word length='46'>of</word><word length='48'>process.</word>
  </line>
  <line>
    <word length='0'>The</word>
    <word length='3'>promise</word><word length='10'>of</word><word length='12'>open</word>
    <word length='16'>source</word><word length='22'>is</word><word length='24'>better</word>
    <word length='30'>quality,</word><word length='38'>higher</word><word length='44'>reliability,</word>
  </line>
  <line>
    <word length='0'>more</word><word length='4'>flexibility,</word><word length='16'>lower</word>
    <word length='21'>cost,</word><word length='26'>and</word><word length='29'>an</word>
    <word length='31'>end</word><word length='34'>to</word><word length='36'>predatory</word>
    <word length='45'>vendor</word>
  </line>
  <line>
    <word length='0'>lock-in.</word>
  </line>
</text>

The XML is then transformed to SVG using the following XSL file

<?xml version="1.0" encoding="UTF-8"?>

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">

<xsl:output encoding="UTF-8"
            method="xml"
            indent="yes"/>
            
  <xsl:template match="text">
    <svg xmlns="http://www.w3.org/2000/svg" width="100%"
                  xmlns:xlink="http://www.w3.org/1999/xlink" >
      <g id="sketch" class="sketch">
        <xsl:apply-templates select="line"/>
      </g>
    </svg>
  </xsl:template>
  
  <xsl:template match="line">
    <xsl:variable name="xfactor">12</xsl:variable>
    <xsl:variable name="yfactor">20</xsl:variable>
    <xsl:variable name="pos" select="position()"></xsl:variable>
    <xsl:apply-templates select="word">
      <xsl:with-param name="xfactor" select="$xfactor"></xsl:with-param>
      <xsl:with-param name="y" select="$pos * $yfactor + 10"></xsl:with-param>
    </xsl:apply-templates>
  </xsl:template>

  <xsl:template match="word">
    <xsl:param name="xfactor"/>
    <xsl:param name="y"/>
    <text xmlns="http://www.w3.org/2000/svg" font-size="12pt" x="{@length * $xfactor +10}" y="{$y}" id="t1"><xsl:value-of select="."/></text>
  </xsl:template>
</xsl:stylesheet>

The final SVG output [twitxr.com] shows 5 lines of text with each word as a separate SVG text element.

<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:variable name="xx">
  <html>
  <body>
  <xsl:call-template name="show_title">
    <xsl:with-param name="title" />
  </xsl:call-template>
  </body>
  </html>
</xsl:variable>

<xsl:template name="show_title" match="/">
  <xsl:param name="title" />
  <xsl:for-each select="catalog/cd">
    <p>Title: <xsl:value-of select="$title" /></p>
  </xsl:for-each>
</xsl:template>

</xsl:stylesheet>

source: XSLT <xsl:param> Element [w3schools.com]