Ruby 2.3 - Add strings after and before certain regexp match

Question

I have a string

text 6ffdfd <a href="http://worldnews.com" target="_blank">toto</a> sdsdsd

I would like to find a regex that would

1. add a opening span tag just after the end of the a tag html link (that is to say to be precise after the string "target="_blank">"
1. add a closing span tag just before the a tag closing

The desired end result would be:

 <a href="http://worldnews.com" target="_blank"><span>toto</span></a> sdsdsd

For the moment , I don't find how to achieve 1, and I only partially managed 2. because my current code is wrongly adding white space that I don't want between /span and the closing a tag

Current code

orig_string = 'text 6ffdfd <a href="http://example.com" target="_blank">toto</a> sdsdsd'
end_result = orig_string.gsub(/<\/a>/, '</span> \\0')
print end_result

I have a set up a online editable DEMO here: https://repl.it/repls/SecondCapitalPika

Do not use regex to parse HTML. Use a proper HTML parser and add the <span> tag to the DOM. — Stefan
– Stefan, Commented Dec 6, 2017 at 14:14
hi Stefan, I am doing it as admin on Active Admin inputs. Why shouldn't I do it with a regexp? I'm a ruby newbie so I thought that could work. Are there security issues ? I want to change the input that I enter so that the one with <span> are saved to the database (instead of the one without <span>s) — Mathieu
– Mathieu, Commented Dec 6, 2017 at 14:15
See The Stack Overflow Regular Expressions FAQ, there are several links explaining why you should not use regular expressions to parse HTML. — Stefan
– Stefan, Commented Dec 6, 2017 at 14:20
Thanks a lot. I went through the very "intense" debate betwene people for and agaisnt using regexp to parse html.In the end I'll go for using it , agreeing with this person "If you have a small set of HTML pages that you want to scrape data from and then stuff into a database, regexes might work fine. For example, I recently wanted to get the names, parties, and districts of Australian federal Representatives, which I got off of the Parliament's web site. This was a limited, one-time job" (source: stackoverflow.com/a/1733489/1467802) — Mathieu
– Mathieu, Commented Dec 6, 2017 at 15:15

Nermin · Accepted Answer · 2017-12-06 15:58:43Z

1

orig_string =~ /(?<=>)([^<]*)(?=<\/a>)/
if $1.present?
  end_result = orig_strig.gsub(/(?<=>)([^<]*)(?=<\/a>)/, '<span>\1</span>')
end

Break down

(?<=>) # to have character >  before
([^<]*) # match everything until character <, match everything in a tag
(?=<\/a>) # to have </a> after

Will result in

print end_result
'text 6ffdfd <a href="http://example.com" target="_blank"><span>toto</span></a> sdsdsd'

edited Dec 6, 2017 at 15:58

answered Dec 6, 2017 at 14:14

Nermin

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5 Comments

Mathieu Over a year ago

could you add just a little more info: indeed this works the first time but if i change the text/input in my admin panel, then the script kick in again and i end up with 4 spans instead of 2:) Could I use some if string contains no span yet, then do this...

Mathieu Over a year ago

aweosme, let me check it. i must really try learning regexp, it seems powerful !

Mathieu Over a year ago

how does $1.present work I mean don't you have to say where you check the presence of $1 ? like on orig_string?

Mathieu Over a year ago

i get undefined method `present?' for nil:NilClass:)

Nermin Over a year ago

nil should return false for present?. Can you try unless $1.blank?

Sebastián Palma · Accepted Answer · 2017-12-06 14:14:43Z

1

If you don't necessarily need a regex, then you could use Nokogiri:

require 'nokogiri'

text = <<-TEXT
  text 6ffdfd <a href="http://worldnews.com" target="_blank">toto</a> sdsdsd
  6ffdfd text <a href="http://worldnews.com" target="_blank">tete</a> sdsdsd
  6ffdfd text <a href="http://worldnews.com">titi</a> sdsdsd
TEXT

doc = Nokogiri.HTML text
doc.css('a[target="_blank"]').each { |anchor| anchor.add_next_sibling '<span>span</span>' }

answered Dec 6, 2017 at 14:14

Sebastián Palma

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1 Comment

Mathieu Over a year ago

Hi Sebastian, thanks for your help. Please refer to my comments under my question where I explain why in the end i still opted for a regexp. On top of those reasons, i also did not want to make my Ruby on Rails 4 more heavy than it already is for a very simple need by importing/requiring another library (nokogiri)

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