Remove everything from a string between two sequences

Question

I have a string in Rails that contains HTML. For example,

<p>01/28/2016 Green RED Horse!!123 456</p>
<a href="http://greenredhorse.com" style="margin-left:283px;margin-
top:50px;margin-bottom:150px;overflow:auto;position:absolute;">
<img alt="Logo" src="http://greenredhorse.com/images/icons/logo.png" 
style="width:266px" /> </a>
<p>01/28/2017 RED Horse!!123 456</p>

How would I go about removing the link tag and everything between its beginning and end from the string?

The end result should look like this.

<p>01/28/2016 Green RED Horse!!123 456</p>
<p>01/28/2017 RED Horse!!123 456</p>

In short: How can I delete everything between <a and </a> inclusively. Without changing the rest of the string.

The tick character in "Logo"` - is it really there or there is a typo? — Wand Maker, Jan 28 '16 at 16:26
You should use a parser when dealing with XML/HTML rather than regular expressions. Parsers are very robust and regex are very fragile when dealing with tags, especially when you don't own and control the generation of that data. See http://stackoverflow.com/questions/1732348/regex-match-open-tags-except-xhtml-self-contained-tags, which covers the issues nicely. — the Tin Man, Jan 28 '16 at 18:12

mtkcs · Accepted Answer · 2019-02-19T16:12:03.007

4

Update: Better regex than the older one below.

string = <<HTML
<a-tag atr="attr">hi<a>atag</a></a-tag>
<a sdf="</a>"> hola</ a>
HTML
pattern = /<a(?:\s*>|\s+(?:(?:[^=\s]*?(?:=(?:(?:"[^"]*?")|(?:'[^']*?')))?)\s*)*>).*?<\/\s*a>/mi

string.gsub!(pattern, '')
puts string #=> <a-tag atr="attr">hi</a-tag>

Older answer

Something like this assuming that html is the string you want to parse

html.gsub! /<a\s?.+?a>/m, ''

You can use this if you have small sets of data similar to the one you posted. If you want a more robust and bug free solution you can use nokogiri, take a look at the answer of the Tin Man.

edited Feb 19 '19 at 16:12

answered Jan 28 '16 at 16:18

mtkcs

1,696
14
27

Thanks, I check this out now! – WhyEnBe Jan 28 '16 at 16:19
So if I am removing an img tag as well(not enclosed in `` I could just also run html.gsub! /\/m, ' ' – WhyEnBe Jan 28 '16 at 16:27
1

If this is **not** the exact string you want to parse *(and a good practice even if it is)*, use the non-greedy quantifier here: `//m`. Also, you might want to be more specific about only capturing the tag, rather than any tag which starts or ends with **a** (note the space after the first **a**): `//m`. Also, to replace all instances, use the **g**lobal flag: `//mg` – Jordan Pilat Jan 28 '16 at 16:33
Don't use that pattern. It will do the wrong thing if there are additional `` tags in the document. http://rubular.com/r/k9k6FLA6IS – the Tin Man Jan 28 '16 at 18:26

score 3 · Answer 2 · answered Jan 28 '16 at 18:17

I wouldn't use regex. Regular expressions might work, but the odds of them breaking when the HTML layout changes are very high.

Instead I'd use:

require 'nokogiri'

doc = Nokogiri::HTML::DocumentFragment.parse(<<EOT)
<p>01/28/2016 Green RED Horse!!123 456</p>
<a href="http://greenredhorse.com" style="margin-left:283px;margin-
top:50px;margin-bottom:150px;overflow:auto;position:absolute;">
<img alt="Logo" src="http://greenredhorse.com/images/icons/logo.png" 
style="width:266px" /> </a>
<p>01/28/2017 RED Horse!!123 456</p>
EOT

doc.at('a').remove

puts doc.to_html
# >> <p>01/28/2016 Green RED Horse!!123 456</p>
# >> 
# >> <p>01/28/2017 RED Horse!!123 456</p>

This is using at which means "find the first occurrence of the desired selector." 'a' is a CSS selector.

Nokogiri is the defacto standard for HTML/XML parsing in Ruby. If you're going to be doing regular work with XML/HTML it is well worth learning to use it.

Thanks I am going to look into this. In my specific case I am dealing with a small data set and the tags format will almost always be the same. — WhyEnBe, Jan 28 '16 at 18:21
@theTinMan I have seen you make edits to my answers to fix grammatical errors and add clarity. You are like WALL-E of StackOverflow :-) — Wand Maker, Jan 28 '16 at 18:59

score 2 · Answer 3 · answered Jan 28 '16 at 16:30

You could use XPath to look up elements of interest.

require 'rexml/document'
include REXML

snippet = <<-eos
<p>01/28/2016 Green RED Horse!!123 456</p>
<a href="http://greenredhorse.com" style="margin-left:283px;margin-
top:50px;margin-bottom:150px;overflow:auto;position:absolute;">
<img alt="Logo" src="http://greenredhorse.com/images/icons/logo.png" 
style="width:266px" /> </a>
<p>01/28/2017 RED Horse!!123 456</p>
eos

well_formed_snippet = "<html>#{snippet}</html>"

xmldoc = Document.new(well_formed_snippet)
p XPath.match(xmldoc, "//p").map(&:to_s)
#=> ["<p>01/28/2016 Green RED Horse!!123 456</p>", "<p>01/28/2017 RED Horse!!123 456</p>"]

Would there be a benefit of doing it this way over using gsub? — WhyEnBe, Jan 28 '16 at 16:48
It depends on your need.. XPath seems to work with XML-like documents, its one of the ways to do it. — Wand Maker, Jan 28 '16 at 16:55

Remove everything from a string between two sequences

3 Answers3

Update: Better regex than the older one below.

Older answer