From: "Florian G. Pflug" <fgp@...>
Date: 2004-10-14T05:24:34+09:00
Subject: Re: [nuby] it seems that (?!...) doesn't work for me

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