command/build: Help text

command/build/command.go

@@ -5,18 +5,19 @@ import (
 	"github.com/mitchellh/packer/packer"
 	"io/ioutil"
 	"log"
+	"strings"
 	"sync"
 )
 
 type Command byte
 
 func (Command) Help() string {
-	return "help"
+	return strings.TrimSpace(helpText)
 }
 
-func (Command) Run(env packer.Environment, args []string) int {
+func (c Command) Run(env packer.Environment, args []string) int {
 	if len(args) != 1 {
-		env.Ui().Error("A single template argument is required.")
+		env.Ui().Say(c.Help())
 		return 1
 	}
 

command/build/help.go

@@ -0,0 +1,8 @@
+package build
+
+const helpText = `
+Usage: packer build TEMPLATE
+
+Will execute multiple builds in parallel as defined in the template.
+The various artifacts created by the template will be outputted.
+`