Set default editor to use with 'gem open' - ruby

Question

How to save the default editor in .gemrc so that I can skip providing the editor with the following command:
gem open GEMNAME [-e EDITOR] [options]

Answer 1

1) Using a .gemrc file:
GEM ENVIRONMENT
...
...
The RubyGems environment can be controlled through command line
arguments, gemrc files, environment variables and built-in defaults.
Command line argument defaults and some RubyGems defaults can be set
in a ~/.gemrc file for individual users and a gemrc in the SYSTEM
CONFIGURATION DIRECTORY for all users. These files are YAML files with
the following YAML keys:
:sources: A YAML array of remote gem repositories to install gems from
:verbose: Verbosity of the gem command. false, true, and :really are the
levels
:update_sources: Enable/disable automatic updating of repository metadata
:backtrace: Print backtrace when RubyGems encounters an error
:gempath: The paths in which to look for gems
:disable_default_gem_server: Force specification of gem server host on push
<gem_command>: A string containing arguments for the specified gem command
http://guides.rubygems.org/command-reference/#gem-environment
Note the last line. For example, if I put the following in ~/.gemrc:
open: -e /Users/7stud/Downloads/macvim-snapshot-74/src/MacVim/mvim
then the command:
$ gem open nokogiri
will open nokogiri in macvim on my system.
2) Using environment variables(per mash's comment):
GEM OPEN
...
...
The open command opens gem in editor and changes current path
to gem's source directory. Editor can be specified with -e option,
otherwise rubygems will look for editor in $EDITOR, $VISUAL and
$GEM_EDITOR variables.
http://guides.rubygems.org/command-reference/
That means if I put something like the following in .bash_profile (or .bashrc):
export GEM_EDITOR="/Users/7stud/Downloads/macvim-snapshot-74/src/MacVim/mvim"
then the command:
$ gem open nokogiri
will open nokogiri in macvim on my system. Don't forget to open a new Terminal window or issue the command:
$ source .bash_profile
to load the changes you made to the environment variables in .bash_profile.