# Replace a string delimited by 2 other string, regexp problem

**URL:** <https://www.ruby-forum.com/t/replace-a-string-delimited-by-2-other-string-regexp-problem/70781>\
**Category:** Ruby\
**Created:** [October 2, 2006, 9:55pm UTC](https://www.ruby-forum.com/t/replace-a-string-delimited-by-2-other-string-regexp-problem/70781 "2006-10-02T21:55:55Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![SSSSSbastien\_Mauret](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/f17d59/32.png) [@SSSSSbastien\_Mauret](https://www.ruby-forum.com/u/SSSSSbastien_Mauret)\
**Post date:** [October 2, 2006, 9:55pm UTC](https://www.ruby-forum.com/t/replace-a-string-delimited-by-2-other-string-regexp-problem/70781/1 "2006-10-02T21:55:55Z")

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Hello,

I want to replace a string in a file who is delimited by 2 other string.  
My problem is to find the start and the end string delimiter and replace  
the content between both.

Ex:  
str = " /\* startdel1 \*/ text1 text1 text1 /_enddel1_/ /_startdel2_/  
text2 text2 text2 /_enddel2_/ /_startdel3_/ text3 text3 text3  
/_enddel3_/ "

In this example i’want to replace the string /_startdel2_/ text2 text2  
text2 /_enddel2_/  
by

/_startdel2_/ hello /_enddel2_/

i’m newbie and it’s a real problem for me to do that.  
help me  
thx

* * *

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<div class="post-metadata">

**Author:** ![SSSSSbastien\_Mauret](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/f17d59/32.png) [@SSSSSbastien\_Mauret](https://www.ruby-forum.com/u/SSSSSbastien_Mauret)\
**Post date:** [October 2, 2006, 10:15pm UTC](https://www.ruby-forum.com/t/replace-a-string-delimited-by-2-other-string-regexp-problem/70781/2 "2006-10-02T22:15:57Z")

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On Tue, Oct 03, 2006 at 04:55:44AM +0900, S?bastien Maurette wrote:

> Hello,
> 
> I want to replace a string in a file who is delimited by 2 other string.  
> My problem is to find the start and the end string delimiter and replace  
> the content between both.

Learn about regular expressions, and then look into the gsub method of  
String. You can get a very brief intro to regular expressions here:  
[http://ruby-doc.org/docs/ProgrammingRuby/html/language.html#UJ](http://ruby-doc.org/docs/ProgrammingRuby/html/language.html#UJ)

---

<div class="post-metadata">

**Author:** ![SSSSSbastien\_Mauret](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/f17d59/32.png) [@SSSSSbastien\_Mauret](https://www.ruby-forum.com/u/SSSSSbastien_Mauret)\
**Post date:** [October 2, 2006, 10:19pm UTC](https://www.ruby-forum.com/t/replace-a-string-delimited-by-2-other-string-regexp-problem/70781/3 "2006-10-02T22:19:58Z")

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Hello !

> Ex:  
> str = " /\* startdel1 \*/ text1 text1 text1 /_enddel1_/ /_startdel2_/  
> text2 text2 text2 /_enddel2_/ /_startdel3_/ text3 text3 text3  
> /_enddel3_/ "
> 
> In this example i’want to replace the string /_startdel2_/ text2 text2  
> text2 /_enddel2_/  
> by
> 
> /_startdel2_/ hello /_enddel2_/

left = “/_startdel2_/”  
right = “/_enddel2_/”  
p str.gsub(/#{Regexp.quote(left)}(.\*?)#{Regexp.quote(right)}/m,  
“#{left}hello#{right}”)

You need the /m as there might be newlines in the match, and you need  
the Regexp.quote as your strings contain characters which lose their  
usual meaning in a regexp (\*).

Cheers !

```
Vince
```

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<div class="post-metadata">

**Author:** ![SSSSSbastien\_Mauret](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/f17d59/32.png) [@SSSSSbastien\_Mauret](https://www.ruby-forum.com/u/SSSSSbastien_Mauret)\
**Post date:** [October 2, 2006, 11:42pm UTC](https://www.ruby-forum.com/t/replace-a-string-delimited-by-2-other-string-regexp-problem/70781/4 "2006-10-02T23:42:13Z")

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Vincent F. wrote:

> left = “/_startdel2_/”  
> right = “/_enddel2_/”  
> p str.gsub(/#{Regexp.quote(left)}(.\*?)#{Regexp.quote(right)}/m,  
> “#{left}hello#{right}”)

The “right” could be in a positive lookahead making things probably a  
likkle bit faster. No lookbehinds until Ruby 1.9 / 2.0 though.

p str.gsub(/#{Regexp.quote(left)}(.\*?)(?=#{Regexp.quote(right)})/m,  
“#{left}hello”)

David V.