From: Matthew Smillie <M.B.Smillie@...>
Date: 2006-07-07T20:08:15+09:00
Subject: Re: Regexp

On Jul 7, 2006, at 11:52, Pe�a, Botp wrote:

> fr fred:
> # When I try this :
> #
> #  @a = "blabla1 blabla1 <math>test1<\math> blabla2 blabla2
> # <math>test2<\math>"
> #  @b = @a.gsub(/<math>.+<\math>/,'ok')
> #
> # I get "blabla1 blabla1 ok" instead of "blabla1 blabla1 ok blabla2
> # blabla2 ok"
> #
> # Could you please help me to tune my regexp so it works the
> # way I want ?
>
> your code works fine here,
>
> irb(main):001:0> @a = "blabla1 blabla1 <math>test1<\math> blabla2  
> blabla2
> irb(main):002:0" <math>test2<\math>"
> => "blabla1 blabla1 <math>test1<math> blabla2 blabla2  
> \n<math>test2<math>"
> irb(main):003:0> @b = @a.gsub(/<math>.+<\math>/,'ok')
> => "blabla1 blabla1 ok blabla2 blabla2 \nok"
>
> (ignore the newline; i just copiednpaste fr your email...)

I thought this might warrant some explanation in light of the later  
posts about greedy operators.

The newline from the paste is what makes this work differently from  
the normal example - greedy expressions (already mentioned) aren't  
greedy across newlines unless you specify a multiline regex, so the  
newline is what made the regex appear correct, when it wouldn't be in  
a general case.

# with newline
a = "blabla1 blabla1 <math>test1<math> blabla2 blabla2  
\n<math>test2<math>"
a.gsub(/<math>.+<\math>/,'ok')
=> "blabla1 blabla1 ok blabla2 blabla2 \nok"

# sans newline
b = "blabla1 blabla1 <math>test1<math> blabla2 blabla2  
<math>test2<math>"
b.gsub(/<math>.+<\math>/,'ok')
=> "blabla1 blabla1 ok"

matthew smillie.