From: James Edward Gray II <james@...>
Date: 2007-02-03T01:03:41+09:00
Subject: Re: bug is ruby regexp

On Feb 2, 2007, at 9:54 AM, Nick Black wrote:

> Hello,
>
> I spotted this problem in ruby's regexp today:
>
> $ irb(main):001:0> num = "10"
> => "10"
> irb(main):002:0> if num =~ /[9-13]/
> irb(main):003:1> puts "hello"
> irb(main):004:1> end
> SyntaxError: compile error
> (irb):2: invalid regular expression: /[9-13]/
>        from (irb):4
>        from :0
> irb(main):005:0>
>
> I have tested it in ruby 1.8 and 0.9.
>
> Anyone else spotted this?

A character class ([...]) with a range of 9-1 is not valid in a  
regular expression because 1 does not come after 9 in your character  
encoding.

I believe you were trying to verify that num is between 9 and 13.   
Your regex would not do this even if it was legal.  Character classes  
give multiple choices for a single character, not a group of characters.

Here are some ways to perform your check:

 >> num = "10"
=> "10"
 >> num =~ /\A(?:9|1[0123])\Z/
=> 0
 >> num.to_i.between? 9, 13
=> true

Hope that helps.

James Edward Gray II