Make --user-install as default

lib/rubygems/commands/install_command.rb

@@ -27,6 +27,10 @@ def initialize
       :without_groups    => [],
     })
 
+    if !File.writable?(Gem.paths.home)
+      defaults.merge!({:user_install => true})
+    end
+
     super 'install', 'Install a gem into the local repository', defaults
 
     add_install_update_options
@@ -43,8 +47,9 @@ def arguments # :nodoc:
   end
 
   def defaults_str # :nodoc:
-    "--both --version '#{Gem::Requirement.default}' --document --no-force\n" +
-    "--install-dir #{Gem.dir} --lock"
+    "--both --version '#{Gem::Requirement.default}' --no-force\n" +
+    "--install-dir #{Gem.dir} --lock\n" +
+    install_update_defaults_str
   end
 
   def description # :nodoc:

lib/rubygems/commands/update_command.rb

@@ -19,9 +19,16 @@ class Gem::Commands::UpdateCommand < Gem::Command
   attr_reader :updated # :nodoc:
 
   def initialize
-    super 'update', 'Update installed gems to the latest version',
+    options = {
       :document => %w[rdoc ri],
       :force    => false
+    }
+
+    if !File.writable?(Gem.paths.home)
+      options.merge!({:user_install => true})
+    end
+
+    super 'update', 'Update installed gems to the latest version', options
 
     add_install_update_options
 
@@ -51,7 +58,8 @@ def arguments # :nodoc:
   end
 
   def defaults_str # :nodoc:
-    "--document --no-force --install-dir #{Gem.dir}"
+    "--no-force --install-dir #{Gem.dir}\n" +
+    install_update_defaults_str
   end
 
   def description # :nodoc:

lib/rubygems/install_update_options.rb

@@ -184,7 +184,11 @@ def add_install_update_options
   # Default options for the gem install command.
 
   def install_update_defaults_str
-    '--document=rdoc,ri --wrappers'
+    default_args = '--document=ri --wrappers'
+    if !File.writable?(Gem.paths.home)
+      default_args += ' --user-install'
+    end
+    default_args
   end
 
 end