From: Joel VanderWerf <vjoel@...>
Date: 2003-06-03T10:21:43+09:00
Subject: Re: case of sub! not working

Ian Macdonald wrote:
> Hi,
> 
> Here's an interesting phenomenon:
> 
> [ianmacd@baghdad]$ irb
> irb(main):001:0> ENV['PATH']
> => "/usr/bin:/bin:/usr/X11R6/bin:/usr/pubsw/bin:/usr/kerberos/bin"
> irb(main):002:0> ENV['PATH'].sub!(%r(:/usr/kerberos/bin), '')
> => "/usr/bin:/bin:/usr/X11R6/bin:/usr/pubsw/bin"
> irb(main):003:0> ENV['PATH']
> => "/usr/bin:/bin:/usr/X11R6/bin:/usr/pubsw/bin:/usr/kerberos/bin"
> irb(main):004:0> puts VERSION
> 1.8.0
> => nil
> 
> Why doesn't the sub! work in line 002? It returns the correct answer,
> but ENV['PATH'] is not modified in-place. I've verified that the
> behaviour is the same in 1.6, too.

ENV is not exactly a Hash, but a singleton that behaves kinda like one. 
Apparently, one difference is that ENV[key] returns a copy of the value. 
(In hash.c, you can verify this by seeing that rb_f_getenv() calls 
rb_str_new2 or rb_tainted_str_new2 to generate the return value.)

So I guess you have to do something like

   ENV['PATH'] = ENV['PATH'].sub(...)