Merge pull request #2707 from jekyll/jekyll-help

lib/jekyll/commands/help.rb

@@ -0,0 +1,33 @@
+module Jekyll
+  module Commands
+    class Help < Command
+      class << self
+
+        def init_with_program(prog)
+          prog.command(:help) do |c|
+            c.syntax 'help [subcommand]'
+            c.description 'Show the help message, optionally for a given subcommand.'
+
+            c.action do |args, _|
+              cmd = (args.first || "").to_sym
+              if args.empty?
+                puts prog
+              elsif prog.has_command? cmd
+                puts prog.commands[cmd]
+              else
+                invalid_command(prog, cmd)
+                abort
+              end
+            end
+          end
+        end
+
+        def invalid_command(prog, cmd)
+          Jekyll.logger.error "Error:", "Hmm... we don't know what the '#{cmd}' command is."
+          Jekyll.logger.info  "Valid commands:", prog.commands.keys.join(", ")
+        end
+
+      end
+    end
+  end
+end