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Ruby Programming
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Where Ruby Finds Its Modules

You use require or load to bring a library module into your Ruby program. Some of these modules are supplied with Ruby, some you installed off the Ruby Application Archive, and some you wrote yourself. How does Ruby find them?

When Ruby is built for your particular machine, it predefines a set of standard directories to hold library stuff. Where these are depends on the machine in question. You can determine this from the command line with something like:

% ruby -e 'puts $:'

On a typical Linux box, you'll probably find something such as:

/usr/local/lib/ruby/site_ruby/1.6/i686-linux
/usr/local/lib/ruby/site_ruby/1.6
/usr/local/lib/ruby/site_ruby
/usr/local/lib/ruby/1.6/i686-linux
/usr/local/lib/ruby/1.6
.

The site_ruby directories are intended to hold modules and extensions that you've added. The architecture-dependent directories (i686-linux in this case) hold executables and other things specific to this particular machine. All these directories are automatically included in Ruby's search for modules.

Sometimes this isn't enough. Perhaps you're working on a large project written in Ruby, and you and your colleagues have built a substantial library of Ruby code. You want everyone on the team to have access to all of this code. You have a couple of options to accomplish this. If your program runs at a safe level of zero (see Chapter 20 beginning on page 253), you can set the environment variable RUBYLIB to a list of one or more directories to be searched.[The separator between entries depends on your platform. For Windows, it's a semicolon; for Unix, a colon.] If your program is not setuid, you can use the command-line parameter -I to do the same thing.

Finally, the Ruby variable $: is an array of places to search for loaded files. This variable is initialized to the list of standard directories, plus any additional ones you specified using RUBYLIB and -I. You can always add additional directories to this array from within your running program.
Ruby Programming
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