How do I replace a specific string with another string? - ruby

Question

I have some content read from an XML file:
page_content = doc.xpath("/somenode/body").inner_text
This content holds some data:
<p> Hello World, ""How are you today""
Hello
etc.
</p>
As you can see, some of the content is wrapped with two pairs of double quotes.
My desired result is to replace the two pairs of double quotes with a single pair:
<p> Hello World, "How are you today"
Hello
etc.
</p>
What I have tried is:
page_content.gsub!(/[""]/, '"')
page_content.gsub!("\"\"", '"')
This does not seem to do the job. Any suggestions on how I can obtain my desired result?

Answer 1

It's important to understand how a parser like Nokogiri works.
To help you, it tries to fix-up damaged/malformed HTML or XML. Your HTML is malformed, so it's GOING to be fixed as Nokogiri parses it, however, that process can make Nokogiri mangle the HTML further. To avoid that, we sometimes have to preprocess the content before we hand it to Nokogiri, or we have to unravel it afterwards by replacing nodes.
require 'nokogiri'
doc = Nokogiri::HTML(<<EOT)
<p> Hello World, ""How are you today""
Hello
etc.
</p>
EOT
That parses the HTML into a DOM.
doc.at('p').to_html
# => "<p> Hello World, \"\"How are you today\"\"\n<a href=\"\" www.hello.comm>Hello</a>\netc.\n</p>"
The text ""How are you today"" was processed without any mangling because it's a text node:
doc.at('p').child.class # => Nokogiri::XML::Text
doc.at('p').child.content # => " Hello World, \"\"How are you today\"\"\n"
That's easily fixed after parsing:
doc.at('p').child.content = doc.at('p').child.content.gsub('""', '"')
# => " Hello World, \"How are you today\"\n"
Trying to fix the parameters of the <a> tag are an entirely different story, because, by that point, Nokogiri has fixed the doubled-quotes, causing the markup to be wrong:
doc.at('a').to_html
# => "<a href=\"\" www.hello.comm>Hello</a>"
Notice that www.hello.comm has been promoted outside its containing quotes.
To fix this requires some preprocessing before handing the HTML to Nokogiri, OR to fix the node and replace the damaged one with the fixed one.
Here's the basis for preprocessing the <a> tag:
html = <<EOT
<p> Hello World, ""How are you today""
Hello
etc.
</p>
EOT
html.gsub(/href=""([^"]+)""/, 'href="\1"')
# => "<p> Hello World, \"\"How are you today\"\"\nHello\netc.\n</p>\n"
If you go that route, don't get fancy. Write small, atomic changes, to avoid your pattern breaking if the HTML changes.
A more robust way (where "robust" is somewhat less than we'd normally get using a parser) is:
bad_a = doc.at('a')
fixed_a = bad_a.to_html.gsub(/""\s([^>]+)>/, '"\1">')
bad_a.replace(fixed_a)
doc.at('p')
# => #(Element:0x3fe4ce9de9e4 {
# name = "p",
# children = [
# #(Text " Hello World, \"How are you today\"\n"),
# #(Element:0x3fe4ce9e0fdc {
# name = "a",
# attributes = [
# #(Attr:0x3fe4ce9e0fa0 {
# name = "href",
# value = "www.hello.comm"
# })],
# children = [ #(Text "Hello")]
# }),
# #(Text "\netc.\n")]
# })
doc.at('p').to_html
# => "<p> Hello World, \"How are you today\"\nHello\netc.\n</p>"
It's possible to use a blanket gsub to massage the text, but that's got a high risk of collateral damage in large/complicated documents. Imagine what would happen to a document if
html.gsub('""', '"')
was used when there are many tags containing empty strings like:
<input value="" name="foo"><input value="" name="bar">
The result of the search/replace would be:
<input value=" name="foo"><input value=" name="bar">
That hardly improves things, and instead would have horribly mangled the document further.
Instead, it's better to surgically fix the problem. Back in the dark, early, pioneer days of the the web, we used to see a huge amount of malformed content, and having to process it with regular expressions was the normal plan of attack. Now, with parsers, we can usually avoid it and can isolate the problem and selectively fix exactly what we want. Looking at the code necessary to do so shows it doesn't take a lot to do it right.

Answer 2

page_content.gsub!('\"\"', '"')

Answer 3

page_content.gsub!(/"{2}/, '"')
rubular.com

Answer 4

a='<p> Hello World, ""How are you today""
Hello
etc.
</p>'
a.gsub! '""', '"'
[19] pry(main)> puts a
<p> Hello World, "How are you today"
Hello
etc.
</p>