Improve CLI usage:

* Rewrite arguments parsing with OptionParser;
* Allow processing of multiple recipes.

lib/producer/core.rb

@@ -1,5 +1,6 @@
 require 'etc'
 require 'forwardable'
+require 'optparse'
 require 'pathname'
 
 require 'net/ssh'

lib/producer/core/cli.rb

@@ -3,8 +3,7 @@ module Producer
     class CLI
       ArgumentError = Class.new(::ArgumentError)
 
-      OPTIONS_USAGE = '[-v] [-n] [-t host.example]'.freeze
-      USAGE = "Usage: #{File.basename $0} #{OPTIONS_USAGE} recipe_file".freeze
+      USAGE = "Usage: #{File.basename $0} [options] [recipes]".freeze
 
       EX_USAGE    = 64
       EX_SOFTWARE = 70
@@ -15,8 +14,8 @@ module Producer
           begin
             cli.parse_arguments!
             cli.run
-          rescue ArgumentError
-            stderr.puts USAGE
+          rescue ArgumentError => e
+            stderr.puts e.message
             exit EX_USAGE
           rescue RuntimeError => e
             stderr.puts "#{e.class.name.split('::').last}: #{e.message}"
@@ -25,40 +24,55 @@ module Producer
         end
       end
 
-      attr_reader :arguments, :env
+      attr_reader :arguments, :stdin, :stdout, :stderr, :env
 
       def initialize(args, stdin: $stdin, stdout: $stdout, stderr: $stderr)
         @arguments  = args
         @stdin      = stdin
         @stdout     = stdout
-        @env        = Env.new(input: stdin, output: stdout, error_output: stderr)
+        @stderr     = stderr
+        @env        = build_env
       end
 
       def parse_arguments!
-        @arguments = arguments.each_with_index.inject([]) do |m, (e, i)|
-          case e
-          when '-v'
-            env.verbose = true
-          when '-n'
-            env.dry_run = true
-          when '-t'
-            env.target = arguments.delete_at i + 1
-          else
-            m << e
-          end
-          m
-        end
-
-        fail ArgumentError unless @arguments.any?
+        option_parser.parse!(@arguments)
+        fail ArgumentError, option_parser if @arguments.empty?
       end
 
       def run(worker: Worker.new(@env))
-        worker.process recipe.tasks
+        evaluate_recipes.each { |recipe| worker.process recipe.tasks }
         @env.cleanup
       end
 
-      def recipe
-        @recipe ||= Recipe::FileEvaluator.evaluate(@arguments.first, env)
+      def evaluate_recipes
+        @arguments.map { |e| Recipe::FileEvaluator.evaluate(e, @env) }
+      end
+
+
+      private
+
+      def build_env
+        Env.new(input: @stdin, output: @stdout, error_output: @stderr)
+      end
+
+      def option_parser
+        OptionParser.new do |opts|
+          opts.banner = USAGE
+          opts.separator ''
+          opts.separator 'options:'
+
+          opts.on '-v', '--verbose', 'enable verbose mode' do |e|
+            env.verbose = true
+          end
+
+          opts.on '-n', '--dry-run', 'enable dry run mode' do |e|
+            env.dry_run = true
+          end
+
+          opts.on '-t', '--target HOST', 'target host' do |e|
+            env.target = e
+          end
+        end
       end
     end
   end