UI update.

- `start` and `stop` now take service ids in parameter and can take
    multiple of them.
  - Errors are displayed properly (instead of “index out of bounds” or
    “nil assertion failed”) when invalid ids are provided on the CLI for
    `start` and `stop`.

src/main.cr

@@ -142,7 +142,10 @@ end
 class Service
 	getter environment : Environment
 	getter providers = ProvidersList.new
-	
+
+	class Exception < ::Exception
+	end
+
 	class ProvidersList < Hash(String, String)
 		def []?(name)
 			super(name).try { |x| Service.get_by_id x}
@@ -405,19 +408,44 @@ begin
 	elsif args[0] == "del"
 		Service.new(args[1], args[2]?).remove RC_DIRECTORY
 	elsif args[0] == "start"
-		#service = Service.new(args[1], args[2]?)
-		service = Service.get_by_id(args[1]).not_nil!
-		service.dependency_tree.flatten.reverse.each do |service|
-			if service.status(PID_DIRECTORY) == Service::Status::Running
-				next
+		services = args[1..args.size].map do |arg|
+			service = Service.get_by_id(arg)
+
+			unless service
+				raise Service::Exception.new "Service '#{arg}' does not exist."
 			end
 
-			puts "starting #{service.to_s}"
-			service.start PID_DIRECTORY, LOG_DIRECTORY
+			service
+		end
+
+		services.each do |service|
+			service.dependency_tree.flatten.reverse.each do |service|
+				if service.status(PID_DIRECTORY) == Service::Status::Running
+					next
+				end
+
+				puts "starting #{service.to_s}"
+				service.start PID_DIRECTORY, LOG_DIRECTORY
+			end
 		end
 	elsif args[0] == "stop"
-		# FIXME: Build revdep tree and stop services started as dependencies?
-		Service.new(args[1], args[2]?).stop PID_DIRECTORY
+		services = args[1..args.size].map do |arg|
+			service = Service.get_by_id(arg)
+
+			unless service
+				raise Service::Exception.new "Service '#{arg}' does not exist."
+			end
+
+			service
+		end
+
+		services.each do |service|
+			# FIXME: Build revdep tree and stop services started as dependencies?
+			if service.status(PID_DIRECTORY) == Service::Status::Running
+				puts "stopping #{service.to_s}"
+				service.stop PID_DIRECTORY
+			end
+		end
 	elsif args[0] == "status"
 		puts Service.new(args[1], args[2]?).status PID_DIRECTORY
 	elsif args[0] == "show"
@@ -451,7 +479,7 @@ begin
 		STDERR << parser << "\n"
 		exit 1
 	end
-rescue e
+rescue e : Service::Exception
 	STDERR << e.message << "\n"
 	exit 2
 end