From: MenTaLguY <mental@...>
Date: 2006-12-07T07:43:34+09:00
Subject: Re: Why is this regex invalid?

On Thu, 7 Dec 2006 07:38:10 +0900, Daniel Finnie <danfinnie@optonline.net> wrote:
> irb(main):002:0> regex = /([0-9]*)([^\+- ]+)(.*)/
> SyntaxError: compile error
> (irb):2: invalid regular expression: /([0-9]*)([^\+- ]+)(.*)/
>          from (irb):2
> 
> irb(main):003:0> regex = /([0-9]*)([^\+ -]+)(.*)/
> => /([0-9]*)([^\+ -]+)(.*)/
> 
> The only thing that it different in the 2 regexps is the placement of
> the space in the square brackets, yet the first regexp is invalid and
> the 2nd valid.
> 
> Why is this?

When an unescaped - appears in any position but the first or final one inside brackets, it is interpreted as a range separator rather than a literal '-'.  Apparently '\+- ' isn't a valid range.

-mental