Improvements to dotenv CLI

This replaces the odd file parsing in the Dotenv::CLI with a proper 
OptionParser implementation that automatically handles converting the 
comma-separated list into an Array and with proper flag support.

This also adds --version and --help flag support to the CLI, since it's 
practically free with OptionParser.

Author: Andrew Nordman

lib/dotenv/cli.rb

@@ -1,4 +1,6 @@
 require "dotenv"
+require "dotenv/version"
+require "optparse"
 
 module Dotenv
   # The CLI is a class responsible of handling all the command line interface
@@ -11,26 +13,55 @@ def initialize(argv = [])
     end
 
     def run
-      filenames = parse_filenames || []
+      parse_argv!(@argv)
+
       begin
-        Dotenv.load!(*filenames)
+        Dotenv.load!(*@filenames)
       rescue Errno::ENOENT => e
         abort e.message
       else
-        exec(*argv) unless argv.empty?
+        exec(*@argv) unless @argv.empty?
       end
     end
 
     private
 
-    def parse_filenames
-      pos = argv.index("-f")
-      return nil unless pos
-      # drop the -f
-      argv.delete_at pos
-      # parse one or more comma-separated .env files
-      require "csv"
-      CSV.parse_line argv.delete_at(pos)
+    def parse_argv!(argv)
+      @filenames = []
+
+      OptionParser.new do |parser|
+        parser.banner = "Usage: dotenv [options]"
+        parser.separator ""
+        add_options(parser)
+      end.parse!(argv)
+
+      @filenames
+    end
+
+    def add_options(parser)
+      add_files_option(parser)
+      add_help_option(parser)
+      add_version_option(parser)
+    end
+
+    def add_files_option(parser)
+      parser.on("-f FILES", Array, "List of env files to parse") do |list|
+        @filenames = list
+      end
+    end
+
+    def add_help_option(parser)
+      parser.on("-h", "--help", "Display help") do
+        puts parser
+        exit
+      end
+    end
+
+    def add_version_option(parser)
+      parser.on("-v", "--version", "Show version") do
+        puts "dotenv #{Dotenv::VERSION}"
+        exit
+      end
     end
   end
 end