What's the difference between GEM_HOME and GEM_PATH?

GEM_PATH provides the locations (there may be several) where gems can be found.

GEM_HOME is where gems will be installed (by default).

(Therefore GEM_PATH should include GEM_HOME).

Also interesting notice. At least on Wndows XP, don't know about other platforms.

Set GEM_HOME in Windows:

C:\>set GEM_HOME=C:\sbox\ruby\dump\.gems

Now let's check this.

1) In Windows ENVs. All OK, as expected:

C:\>set
...
GEM_HOME=C:\sbox\ruby\dump\.gems
...

2) With gem env. Notice it puts GEM_HOME along with GEM_PATHs but at the first place:

C:\>gem env
RubyGems Environment:
  - RUBYGEMS VERSION: 2.0.3
  - RUBY VERSION: 2.0.0 (2013-02-24 patchlevel 0) [i386-mingw32]
  - INSTALLATION DIRECTORY: C:/sbox/ruby/dump/.gems
  - RUBY EXECUTABLE: C:/Ruby200/bin/ruby.exe
  - EXECUTABLE DIRECTORY: C:/sbox/ruby/dump/.gems/bin
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86-mingw32
  - GEM PATHS:
     - C:/sbox/ruby/dump/.gems
     - C:/Documents and Settings/User/.gem/ruby/2.0.0
     - C:/Ruby200/lib/ruby/gems/2.0.0
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - https://rubygems.org/

3) Now with bundle env:

C:\>bundle env
Bundler 1.3.4
Ruby 2.0.0 (2013-02-24 patchlevel 0) [i386-mingw32]
Rubygems 2.0.3
GEM_HOME C:\sbox\ruby\dump\.gems
GEM_PATH

GEM_PATH is empty, it means default value. But from where does it take the default value? See gem env.