Add support for a default-gems file

https://github.com/asdf-vm/asdf-ruby/issues/31

README.md

@@ -19,6 +19,18 @@ When installing Ruby using `asdf install`, you can pass custom configure options
 * `RUBY_CONFIGURE_OPTIONS` - use only your configure options
 * `RUBY_EXTRA_CONFIGURE_OPTIONS` - append these configure options along with ones that this plugin already uses
 
+## Default gems
+
+asdf-ruby can automatically install a set of default gems right after
+installing a Ruby version. To enable this feature, provide a
+`$HOME/.default-gems` file that lists one gem per line, for example:
+
+```
+bundler
+pry
+gem-ctags
+```
+
 ## Migrating from another Ruby version manager
 
 ### `.ruby-version` file

bin/install

@@ -218,4 +218,24 @@ get_ruby_type() {
 }
 
 
+install_default_gems() {
+  local default_gems="${HOME}/.default-gems"
+
+  if [ ! -f $default_gems ]; then return; fi
+
+  echo ""
+
+  for name in $(cat $default_gems); do
+    echo -n "Installing ${name} gem... "
+
+    if gem install $name > /dev/null 2>&1; then
+      echo "SUCCESS"
+    else
+      echo "FAIL"
+    fi
+  done
+}
+
+
 install_ruby $ASDF_INSTALL_TYPE $ASDF_INSTALL_VERSION $ASDF_INSTALL_PATH
+install_default_gems