From: Joel VanderWerf <vjoel@...>
Date: 2008-04-15T08:16:41+09:00
Subject: Re: How to reliably setup require path

Christian Johansen wrote:
> I'm writing my first Ruby command line application (beyond a simple
> script) and I'm little unsure about how to structure the application and
> the best use of require. I've come as far as to have the following file
> structure:
> 
> myapp/
>   bin/
>     myapp
>   docs/ (RDOC files)
>   lib/
>     myapp.rb
>     myapp/
>       files and folders here
>   test/ (Test::Unit tests)
> 
> And the application is working, but there are a few things of which I am
> unsure:
> 
> The bin/myapp file is a symlink to the lib/myapp.rb file which has a
> shebang line. This doesn't really work, because inside lib/myapp.rb I
> have:
> 
> require 'myapp/file'
> require 'myapp/module/file'
> 
> which doesn't make sense when running the application from anywhere else
> than myapp/lib
> 
> I also tried
> 
> $MYAPP_ROOT = File.expand_path(File.join(File.dirname(__FILE__),
> 'myapp'))
> $LOAD_PATH << File.expand_path($MYAPP_ROOT)
> 
> Which still doesn't work because this also relies on cwd...
> 
> How do I work around this? What's the best practice way of making these
> things make sense? Do you use the $RUBYLIB variable to set the full path
> to the application? I was hoping to create the application as standalone
> as possible, so installation will be easy.


I'd do a couple of things differently (and I've used this pattern in a 
number of applications with the same dir structure as yours):

1. make bin/myapp a very short ruby script instead of a symlink (if you 
want this to work on windows, symlinks won't work anyway).

2. use unshift instead of <<, so you get precedence

3. use an ENV var instead of a global so child scripts can use it

4. use File.dirname to go up two levels instead of one, so that you can 
use it to find non-lib files as well (images for example, or other data 
files). Note that the expand_path call has to happen before calling 
dirname twice.

Here's the code:

ENV['MYAPP_BASE'] = File.dirname(File.dirname(File.expand_path(__FILE__)))
libdir = File.join(ENV['MYAPP_BASE'], "lib")
$LOAD_PATH.unshift libdir
ENV['RUBYLIB'] = libdir + ":" + ENV['RUBYLIB']

HTH.

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407