I found this post that covers the discussion of introducing a new Ruby Kernel
__dir__, which would return the current directory
containing the source code file,
Problem File.dirname(__FILE__) is frequently used and too long. Analysis There are 222 uses of __FILE__ listed by the google code search, classified into these categories: (A) 30.6% (68) are used with require and File.dirname. In Ruby 1.9.2, this case is supported by require_relative. (B) 31.1% (69) are with File.dirname, but not with require. For example, reading data files of unit tests. (C) 21.6% (48) are the idiom, $0 == __FILE__. B is as many as A (and even more than C), so it is reasonable to add a shortcut for File.dirname(__FILE__) in addition to require_relative. * code: http://gist.github.com/170336 * result: http://route477.net/files/__file__.html Solutions (1) add a toplevel constant __DIR__ pros: looks like __FILE__ cons: adding new keyword (2) add Kernel#__DIR__ pros: no new keyword cons: it should have a lower-case name (like 1.9's __method__), because it is not a constant but a method. (3) add Kernel#__dir__ pros: no new keyword, and it is clearer than (4) that it has some associations with __FILE__. (4) make __FILE__ to the default argument of File.dirname pros: no new keyword nor new method cons: it is not clear that 'File.dirname' is expanded to the path of directory of __FILE__. = Conclusion I think (3) (Kernel#__dir__) is the best.
So now you know. The command,
__dir__, is a Ruby Kernel method and not a constant, like