# Need help with a regexp **URL:** \ **Category:** Ruby\ **Created:** [December 8, 2006, 4:15am UTC](https://www.ruby-forum.com/t/need-help-with-a-regexp/78736 "2006-12-08T04:15:43Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![rpheath](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/73ab20/32.png) [@rpheath](https://www.ruby-forum.com/u/rpheath)\ **Post date:** [December 8, 2006, 4:15am UTC](https://www.ruby-forum.com/t/need-help-with-a-regexp/78736/1 "2006-12-08T04:15:43Z")
I’m trying to write a regular expression to replace a ``` … ``` block or a > … block with a blank (’’). I can only get the ``` … ``` to work correctly. Here’s what I have: text.gsub(/^ ``` [^<]_\$|^_ _> (._ ?)

$/,’’) Can someone help me figure out why the blockquote is still showing up??? Thanks in advance. ``` ---
**Author:** ![rpheath](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/73ab20/32.png) [@rpheath](https://www.ruby-forum.com/u/rpheath)\ **Post date:** [December 8, 2006, 4:47am UTC](https://www.ruby-forum.com/t/need-help-with-a-regexp/78736/2 "2006-12-08T04:47:46Z")
Why are you doing a gsub but then anchoring the Regexp to the start & ends? Use a normal sub or take out all the ^s and $s (except for the character class definitions, i.e., the ones in square brackets). Please post some sample text, not of what you would like to remove but of what you would like to remove it from. Dan ---
**Author:** ![rpheath](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/73ab20/32.png) [@rpheath](https://www.ruby-forum.com/u/rpheath)\ **Post date:** [December 8, 2006, 4:55am UTC](https://www.ruby-forum.com/t/need-help-with-a-regexp/78736/3 "2006-12-08T04:55:46Z")
Thanks for the reply. I’m relatively new to regular expressions, and misinterpretted the ^s and $s. I was thinking they were for that specific check, so it was either the first string “|” (or) the second string. ## Here’s sample text that would be passed into it. This is the first sentence. Now I'll post a code snippet: ``` def strip_blocks(text) text.gsub([regex],'') end ``` This is another sentence before the block quote. > This is a quote ## This is one more sentence What I would like to have left is this: * * * This is the first sentence. Now I'll post a code snippet: This is another sentence before the block quote. ## This is one more sentence Hopefully that helps. Sorry the question is not organized and kind of basic, but I’m new to this. Thanks again for any help. ---
**Author:** ![rpheath](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/73ab20/32.png) [@rpheath](https://www.ruby-forum.com/u/rpheath)\ **Post date:** [December 8, 2006, 6:25am UTC](https://www.ruby-forum.com/t/need-help-with-a-regexp/78736/4 "2006-12-08T06:25:52Z")
You are missing the ‘m’ flag which will allow ‘.’ to match new lines pre\_match = / ``` ._?\<\pre\>/m block\_match = /_ _> ._ ?: ._?\._?\/m ``` ---
**Author:** ![rpheath](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/73ab20/32.png) [@rpheath](https://www.ruby-forum.com/u/rpheath)\ **Post date:** [December 8, 2006, 3:40pm UTC](https://www.ruby-forum.com/t/need-help-with-a-regexp/78736/5 "2006-12-08T15:40:45Z")
On Dec 7, 2006, at 10:55 PM, rpheath wrote: > Thanks for the reply. I’m relatively new to regular expressions, and > misinterpretted the ^s and $s. I was thinking they were for that > specific check, so it was either the first string “|” (or) the second > string. [http://groups.google.com/group/rubyonrails-talk/browse\_frm/thread/](http://groups.google.com/group/rubyonrails-talk/browse_frm/thread/) 6c75d5d4df368186/2743494eb303014c#2743494eb303014c And might I suggest picking ONE mailing list on which to ask your questions (Ruby is actually the better one for this question about regular expressions), and then JUST ASK ONCE. -Rob Rob B. [http://agileconsultingllc.com](http://agileconsultingllc.com) removed\_email\_address@domain.invalid ---
**Author:** ![rpheath](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/73ab20/32.png) [@rpheath](https://www.ruby-forum.com/u/rpheath)\ **Post date:** [December 8, 2006, 6:17am UTC](https://www.ruby-forum.com/t/need-help-with-a-regexp/78736/6 "2006-12-08T06:17:29Z")
rpheath wrote: > Thanks for the reply. I’m relatively new to regular expressions, and > misinterpretted the ^s and $s. I was thinking they were for that > specific check, so it was either the first string “|” (or) the second > string. > > ## Here’s sample text that would be passed into it. > > This is the first sentence. Now I'll post a code snippet: > > ``` > def strip_blocks(text) > text.gsub([regex],'') > end > ``` > > This is another sentence before the block quote. > > > This is a quote > > This is one more sentence > > ---------------------- > > What I would like to have left is this: > > * * * > > This is the first sentence. Now I'll post a code snippet: > > This is another sentence before the block quote. > > This is one more sentence > > ---------------------- > > Hopefully that helps. Sorry the question is not organized and kind of > basic, but I’m new to this. Thanks again for any help. Try this. It uses the “non-greedy” operator ‘?’ and multiline case-insensitive matching. Not using the ‘non-greedy’ operator would gobble up everything between two tags, including nested tags of the same name. This is probably not what you would want. def remove\_tag\_block(tag, text) text.gsub(/\<#{tag}\>.\*?\/im, ‘’) end irb(main):054:0\> text =\> “ This is the first sentence. Now I’ll post a code snippet: \n\n ``` \ndef strip_blocks(text)\n text.gsub([regex],‘’)\nend\n ``` \n\n This is another sentence before the block quote. \n\n > \n > > This is a > quote > > \n \n\n This is one more sentence ” irb(main):055:0\> t=remove\_tag\_block(“pre”, text) =\> “ This is the first sentence. Now I’ll post a code snippet: \n\n\n\n This is another sentence before the block quote. \n\n > \n > > This is a > quote > > \n \n\n This is one more sentence ” irb(main):056:0\> remove\_tag\_block(“blockquote”, t) =\> “ This is the first sentence. Now I’ll post a code snippet: \n\n\n\n This is another sentence before the block quote. \n\n\n\n This is one more sentence ” The problem is that this won’t work with nested tags, e.g. | stuff | irb(main):065:0\> x=“ | stuff | ” =\> “ | stuff | ” irb(main):066:0\> remove\_tag\_block(“table”, x) =\> “” This is because _regular_ regular expressions 🙂 can’t match nested pairs, such as “((()(())()))”. I think I read somewhere a phrase that regexp’s can’t count. You have to use _recursive_ regular expressions, which are found in PCRE (Perl RE), but AFAIK not in the current Ruby regexp engine. Maybe Oniguruma has it - I dunno. I saw a PCRE extension for Ruby somewhere, but I don’t know anything about it. The Perl RE for matching nested parentheses is apparently as follows (from [The Joy of Regular Expressions [1] — SitePoint](http://www.sitepoint.com/blogs/2006/09/26/the-joy-of-regular-expressions-1/)) (((?\>[^()]+)|(?R))\*) I believe that to do this correctly without PCRE, you have to resort to some text parsing or use a SAX parser or similar. Maybe some Ruby guru (i.e. not me) will be able to pull out an RE or some easy way to do this.