Added Ruby gems script

Necessary to provide a single source of truth for installing Ruby
dependencies. This used to be managed by the Ruby Setup project but
that project is being deprecated in favor of this project.

lib/installers.sh

@@ -188,6 +188,19 @@ install_program() {
 }
 export -f install_program
 
+# Installs Ruby.
+# Parameters: None.
+install_ruby() {
+  local version="$(cat $HOME/.ruby-version | tr -d '\n')"
+
+  if [[ ! -x "$(command -v ruby)" && -n $(ruby --version | grep --quiet "$version") ]]; then
+    $(get_homebrew_bin_root)/ruby-install "ruby-$version"
+    chruby "$version"
+    gem update --system && gem update
+  fi
+}
+export -f install_ruby
+
 # Installs Rust.
 # Parameters: None.
 install_rust() {

lib/options.sh

@@ -22,6 +22,8 @@ process_option() {
       bin/install_applications;;
     'x')
       bin/install_extensions;;
+    'rg')
+      bin/install_ruby_gems;;
     'rc')
       bin/install_rust_crates;;
     'd')
@@ -37,6 +39,7 @@ process_option() {
       bin/install_app_store
       bin/install_applications
       bin/install_extensions
+      bin/install_ruby_gems
       bin/install_rust_crates
       bin/apply_default_settings
       bin/setup_software
@@ -50,6 +53,7 @@ process_option() {
       verify_app_store_applications
       verify_applications
       verify_extensions
+      verify_ruby_gems
       verify_rust_crates;;
     'C')
       caffeinate_machine;;

lib/verifiers.sh

@@ -127,6 +127,23 @@ verify_path() {
 }
 export -f verify_path
 
+# Checks for missing Ruby gems.
+verify_ruby_gems() {
+  local gems="$(gem list --no-versions)"
+
+  printf "\nChecking Ruby gems...\n"
+
+  while read line; do
+    if [[ "$line" == "gem install"* ]]; then
+      local gem=$(printf "$line" | awk '{print $3}')
+      verify_listed_application "$gem" "${gems[*]}"
+    fi
+  done < "$MAC_OS_CONFIG_PATH/bin/install_ruby_gems"
+
+  printf "Ruby gems check complete.\n"
+}
+export -f verify_ruby_gems
+
 # Checks for missing Rust crates.
 verify_rust_crates() {
   printf "\nChecking Rust crates...\n"