From: Lionel Thiry <lthiry@...>
Date: 2004-10-15T07:14:15+09:00
Subject: Re: [nuby] it seems that (?!...) doesn't work for me

Florian G. Pflug a �crit :

> Lionel Thiry wrote:
> 
>> I'd like to make some kind of substitution like in a shell: "${var}". 
>> For that purpose, I use this pattern: /\$\{(.*?)\}/.
>>
>> But I also want to be able to escape those special caracters $, { and 
>> }. Examples:
>> "${var\\}weird}" # which is a variable with "var{weird" as name
>> "\\${var}" # which is the simple string "${var}" with no substitution
> 
> 
> Use: /(^|[^\\]|(\\\\)+)\$\{(([^\}\\]|(\\.))*)\}/
> 
> I testes this with:
> puts 
> (STDIN.readlines.join("\n").gsub(/(^|[^\\]|(\\\\)+)\$\{(([^\}\\]|(\\.))*)\}/m) 
> {|m| "#{$1}--#{$3.gsub(/\\(.)/, "\\1")}--"})
> And it seems to work (replaces ${var} with --var--, but only if not 
> escaped).
> 
> The first part (/(^|[^\\]|(\\\\)+)/) basically means "either 
> start-of-string, non-backslash, or an even amount of backslash".
> The part (/\{(([^\}\\]|(\\.))*)\}/) means "start with {, and than allow 
> any number of groups that consist of either a sequence of non-} and 
> non-\, or
> of an escaped character (/\\./).
> 
> greetings, Florian Pflug

Thanks a lot for the help, but the pattern you gave is not perfect:

re = /(^|[^\\]|(\\\\)+)\$\{(([^\}\\]|(\\.))*)\}/
'pre${var}'.match # => prematch is "pr"

Lionel Thiry