How is the default Ruby LOAD_PATH determined?

Question

Assuming I compile my own fresh Ruby (MRI 1.9.3), what is the default LOAD_PATH, and how is that computed?

Answer 1

On my machine, the initial load path looks like this:

$ ruby -e 'puts $LOAD_PATH'
/Users/matt/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1
/Users/matt/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/x86_64-darwin10.8.0
/Users/matt/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby
/Users/matt/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/vendor_ruby/1.9.1
/Users/matt/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/vendor_ruby/1.9.1/x86_64-darwin10.8.0
/Users/matt/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/vendor_ruby
/Users/matt/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1
/Users/matt/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/x86_64-darwin10.8.0

Armed with grep, an investigation into the Ruby source leads to the definition of ruby_initial_load_paths[] in version.c (this is on Ruby 1.9.3). The first of these that apply (neither NO_INITIAL_LOAD_PATH or RUBY_SEARCH_PATH have been set) is RUBY_SITE_LIB2. Looking at the defines above that definition we see:

#define RUBY_SITE_LIB2              RUBY_SITE_LIB    "/"RUBY_LIB_VERSION

and in turn:

#define RUBY_SITE_LIB RUBY_LIB_PREFIX"/site_ruby"

Following this chain of defines, it becomes clear that this corresponds to the first entry in my load path above. Similarly the other constants that go into this variable correspond to the other load path entries.

The ruby_initial_load_paths[] variable is used in ruby_init_loadpath_safe() in ruby.c, where the actual load path is set up for the process.

So the answer to your question is that the initial load path is set at compile time with some #defines, according to how the build has been configured.

Answer 2

Your compilation create a lib directory on *nix based systems it is generally

/usr/lib/ruby/X.Y.Z

X.Y.Z represents version number of your ruby C api version.