Regular expression to remove only beginning and end html tags from string? - ruby-on-rails

Question

I would like to remove for example <div><p> and </p></div> from the string below. The regex should be able to remove an arbitrary number of tags from the beginning and end of the string.
<div><p>text to <span class="test">test</span> the selection on.
Kibology for <b>all</b><br>. All <i>for</i> Kibology.</p></div>
I have been tinkering with rubular.com without success. Thanks!

Answer 1

def remove_html_end_tags(html_str)
html_str.match(/\<(.+)\>(?!\W*\<)(.+)\<\/\1\>/m)[2]
end
I'm not seeing the problem of \<(.+)> consuming multiple opening tags that Alan Moore pointed out below, which is odd because I agree it's incorrect. It should be changed to \<([^>\<]+)> or something similar to disambiguate.
def remove_html_end_tags(html_str)
html_str.match(/\<([^\>\<]+)\>(?!\W*?\<)(.+)\<\/\1\>/m)[2]
end
The idea is that you want to capture everything between the open/close of the first tag encountered that is not followed immediately by another tag, even with spaces between.
Since I wasn't sure how (with positive lookahead) to say give me the first key whose closing angle bracket is followed by at least one word character before the next opening angle bracket, I said
\>(?!\W*\<)
find the closing angle bracket that does not have all non-word characters before the next open angle bracket.
Once you've identified the key with that attribute, find its closing mate and return the stuff between.
Here's another approach. Find tags scanning forward and remove the first n. Would blow up with nested tags of the same type, but I wouldn't take this approach for any real work.
def remove_first_n_html_tags(html_str, skip_count=0)
matches = []
tags = html_str.scan(/\<([\w\s\_\-\d\"\'\=]+)\>/).flatten
tags.each do |tag|
close_tag = "\/%s" % tag.split(/\s+/).first
match_str = "<#{tag}>(.+)<#{close_tag}>"
match = html_str.match(/#{match_str}/m)
matches << match if match
end
matches[skip_count]
end

Answer 2

Still involves some programming:
str = '<div><p>text to <span class="test">test</span> the selection on.
Kibology for <b>all</b><br>. All <i>for</i> Kibology.</p></div>'
while (m = /\A<.+?>/.match(str)) && str.end_with?('</' + m[0][1..-1])
str = str[m[0].size..-(m[0].size + 2)]
end
Cthulhu you out there?

Answer 3

I am going to go ahead and answer my own question. Below is the programmatic route:
The input string goes into the first loop as an array in order to remove the front tags. The resulting string is looped through in reverse order in order to remove the end tags. The string is then reversed in order to put it in the correct order.
def remove_html_end_tags(html_str)
str_no_start_tag = ''
str_no_start_and_end_tag = ''
a = html_str.split("")
i= 0
is_text = false
while i <= (a.length - 1)
if (a[i] == '<') && !is_text
while (a[i] != '>')
i+= 1
end
i+=1
else
is_text = true
str_no_start_tag << a[i]
i+=1
end
end
a = str_no_start_tag.split("")
i= a.length - 1
is_text = false
while i >= 0
if (a[i] == '>') && !is_text
while (a[i] != '<')
i-= 1
end
i-=1
else
is_text = true
str_no_start_and_end_tag << a[i]
i-=1
end
end
str_no_start_and_end_tag.reverse!
end

Answer 4

(?:\<div.*?\>\<p.*?\>)|(?:\<\/p\>\<\/div\>) is the expression you need. But this doesn't check for every scenario... if you are trying to parse any possible combination of tags, you may want to look at other ways to parse.
Like for example, this expression doesn't allow for any whitespace between the div and p tag. So if you wanted to allow for that, you would add \s* inbetween the \>\< sections of the tag like so: (?:\<div.*?\>\s*\<p.*?\>)|(?:\<\/p\>\s*\<\/div\>).
The div tag and the p tag are expected to be lowercase, as the expression is written. So you may want to figure out a way to check for upper or lower case letters for each, so that Div or dIV would be found too.
Use gskinner's RegEx tool for testing and learning Regular Expressions.
So your end ruby code should look something like this:
# Ruby sample for showing the use of regular expressions
str = "<div><p>text to <span class=\"test\">test</span> the selection on.
Kibology for <b>all</b><br>. All <i>for</i> Kibology.</p></div>"
puts 'Before Reguar Expression: "', str, '"'
str.gsub!(/(?:\<div.*?\>\s*\<p.*?\>)|(?:\<\/p\>\s*\<\/div\>)/, "")
puts 'After Regular Expression', str
system("pause")
EDIT: Replaced div*? to div.*? and replaced p*? to p.*? per suggestions in the comments.
EDIT: This answer doesn't allow for any set of tags, just the two listed in the first line of the question.