core: add "apply -confirm" flag

A common reason to want to use `terraform plan` is to have a chance to
review and confirm a plan before running it.  If in fact that is the
only reason you are running plan, this new `terraform apply -confirm`
flag provides an easier alternative to

    P=$(mktemp -t plan)
    terraform refresh
    terraform plan -refresh=false -out=$P
    terraform apply $P
    rm $P

command/apply.go

@@ -27,7 +27,8 @@ type ApplyCommand struct {
 }
 
 func (c *ApplyCommand) Run(args []string) int {
-	var destroyForce, refresh bool
+	var destroyForce, refresh, confirm bool
+	var moduleDepth int
 	args = c.Meta.process(args, true)
 
 	cmdName := "apply"
@@ -40,6 +41,10 @@ func (c *ApplyCommand) Run(args []string) int {
 		cmdFlags.BoolVar(&destroyForce, "force", false, "force")
 	}
 	cmdFlags.BoolVar(&refresh, "refresh", true, "refresh")
+	if !c.Destroy {
+		cmdFlags.BoolVar(&confirm, "confirm", false, "confirm plan before applying")
+		c.addModuleDepthFlag(cmdFlags, &moduleDepth)
+	}
 	cmdFlags.IntVar(
 		&c.Meta.parallelism, "parallelism", DefaultParallelism, "parallelism")
 	cmdFlags.StringVar(&c.Meta.statePath, "state", DefaultStateFilename, "path")
@@ -111,6 +116,10 @@ func (c *ApplyCommand) Run(args []string) int {
 			"Destroy can't be called with a plan file."))
 		return 1
 	}
+	if confirm && planned {
+		c.Ui.Error("Cannot confirm with a plan file.")
+		return 1
+	}
 	if !destroyForce && c.Destroy {
 		// Default destroy message
 		desc := "Terraform will delete all your managed infrastructure.\n" +
@@ -162,11 +171,36 @@ func (c *ApplyCommand) Run(args []string) int {
 			}
 		}
 
-		if _, err := ctx.Plan(); err != nil {
+		plan, err := ctx.Plan()
+		if err != nil {
 			c.Ui.Error(fmt.Sprintf(
 				"Error creating plan: %s", err))
 			return 1
 		}
+
+		if confirm {
+			c.Ui.Output(strings.TrimSpace(confirmHeader) + "\n")
+			c.Ui.Output(FormatPlan(&FormatPlanOpts{
+				Plan:        plan,
+				Color:       c.Colorize(),
+				ModuleDepth: moduleDepth,
+			}))
+			desc := "Terraform will apply the plan described above.\n" +
+				"Only 'yes' will be accepted to confirm."
+			v, err := c.UIInput().Input(&terraform.InputOpts{
+				Id:          "confirm",
+				Query:       "Do you want to apply the plan above?",
+				Description: desc,
+			})
+			if err != nil {
+				c.Ui.Error(fmt.Sprintf("Error asking for confirmation: %s", err))
+				return 1
+			}
+			if v != "yes" {
+				c.Ui.Output("Apply cancelled.")
+				return 1
+			}
+		}
 	}
 
 	// Setup the state hook for continuous state updates
@@ -299,8 +333,14 @@ Options:
                          modifying. Defaults to the "-state-out" path with
                          ".backup" extension. Set to "-" to disable backup.
 
+  -confirm               Display the plan and ask for confirmation before applying.
+
   -input=true            Ask for input for variables if not directly set.
 
+  -module-depth=n        Specifies the depth of modules to show when using -confirm.
+                         This does not affect the plan itself, only the output
+                         shown. By default, this is -1, which will expand all.
+
   -no-color              If specified, output won't contain any color.
 
   -parallelism=n         Limit the number of concurrent operations.
@@ -430,3 +470,11 @@ func outputsAsString(state *terraform.State, schema []*config.Output, includeHea
 
 	return strings.TrimSpace(outputBuf.String())
 }
+
+const confirmHeader = `
+The Terraform execution plan has been generated and is shown below.
+Resources are shown in alphabetical order for quick scanning. Green resources
+will be created (or destroyed and then created if an existing resource
+exists), yellow resources are being changed in-place, and red resources
+will be destroyed. Cyan entries are data sources to be read.
+`

website/source/docs/commands/apply.html.markdown

@@ -33,6 +33,8 @@ The command-line flags are all optional. The list of available flags are:
 
 * `-input=true` - Ask for input for variables if not directly set.
 
+* `-confirm` - Display the plan and ask for confirmation before applying.
+
 * `-no-color` - Disables output with coloring.
 
 * `-parallelism=n` - Limit the number of concurrent operation as Terraform