Add check for BUNDLE_GEMFILE in cli

lib/bundler/cli.rb

@@ -34,11 +34,13 @@ def initialize(*args)
       super
 
       custom_gemfile = options[:gemfile] || Bundler.settings[:gemfile]
-      if custom_gemfile && !custom_gemfile.empty?
+
+      if custom_gemfile && !custom_gemfile.empty? && !ENV["BUNDLE_GEMFILE"]
         Bundler::SharedHelpers.set_env "BUNDLE_GEMFILE", File.expand_path(custom_gemfile)
-        Bundler.reset_paths!
       end
 
+      Bundler.reset_paths!
+
       Bundler.settings.set_command_option_if_given :retry, options[:retry]
 
       current_cmd = args.last[:current_command].name

spec/bundler/cli_spec.rb

@@ -38,16 +38,51 @@
     end
   end
 
-  context "when ENV['BUNDLE_GEMFILE'] is set to an empty string" do
-    it "ignores it" do
-      gemfile bundled_app("Gemfile"), <<-G
+  context "behaviour with ENV['BUNDLE_GEMFILE']" do
+    before do
+      gemfile bundled_app("Gemfile.dev"), <<-G
         source "file://#{gem_repo1}"
         gem 'rack'
       G
 
-      bundle :install, :env => { "BUNDLE_GEMFILE" => "" }
+      bundle! "config --local gemfile #{bundled_app("Gemfile.dev")}"
+    end
+
+    context "when not specified" do
+      it "uses the value specified in config file" do
+        bundle :install
+        bundle :list
+
+        expect(out).to include "rack (1.0.0)"
+      end
+    end
+
+    context "when set to an empty string" do
+      it "ignores it and searches for default gemfiles" do
+        gemfile bundled_app("Gemfile"), <<-G
+          source "file://#{gem_repo1}"
+          gem 'rack'
+        G
 
-      expect(the_bundle).to include_gems "rack 1.0.0"
+        bundle :install, :env => { "BUNDLE_GEMFILE" => "" }
+
+        expect(the_bundle).to include_gems "rack 1.0.0"
+      end
+    end
+
+    context "when passed a value" do
+      it "uses specified gemfile" do
+        with_env_vars("BUNDLE_GEMFILE" => "Gemfile.other") do
+          gemfile bundled_app("Gemfile.other"), <<-G
+            source "file://#{gem_repo1}"
+            gem 'rack'
+          G
+
+          bundle :install
+
+          expect(the_bundle).to include_gems "rack 1.0.0"
+        end
+      end
     end
   end