>  ruby -I . ../mycode.rb data/mii.iv
>  src/emitter.rb:404: warning: character class has `[' without escape
> 
> I cannot find src/emitter.rb. It is not in my code, it is not
> in the ruby source, nor is it in the ruby install directory.
> 
> I don't know where else to look.
> Is this a bug in the error message? Is it real?

emitter.rb is part of YAML.

Search for a line like
	while str =~ /^\/([^\/[]+)(?:\[([^\]]+)\])?/
(I have it in line 271... my version of yaml is old),

and change the [^\/[] to [^\/\[] . This should do it, I think.
Ruby issues this warning since 1.8 I think.