cli: "terraform state list" -id argument

A new -id option to "terraform state list" which constraints the output of the command to resources whose id is equal to the flag value.

command/state_list.go

@@ -23,6 +23,7 @@ func (c *StateListCommand) Run(args []string) int {
 
 	cmdFlags := c.Meta.flagSet("state list")
 	cmdFlags.StringVar(&c.Meta.statePath, "state", DefaultStateFilename, "path")
+	lookupId := cmdFlags.String("id", "", "Restrict output to paths with a resource having the specified ID.")
 	if err := cmdFlags.Parse(args); err != nil {
 		return cli.RunResultHelp
 	}
@@ -62,10 +63,12 @@ func (c *StateListCommand) Run(args []string) int {
 	}
 
 	for _, result := range results {
-		if _, ok := result.Value.(*terraform.InstanceState); ok {
+		if i, ok := result.Value.(*terraform.InstanceState); ok {
+			if *lookupId == "" || i.ID == *lookupId {
 				c.Ui.Output(result.Address)
 			}
 		}
+	}
 
 	return 0
 }
@@ -94,6 +97,8 @@ Options:
                       up Terraform-managed resources. By default it will
                       use the state "terraform.tfstate" if it exists.
 
+  -id=ID              Restricts the output to objects whose id is ID.
+
 `
 	return strings.TrimSpace(helpText)
 }

command/state_list_test.go

@@ -37,6 +37,65 @@ func TestStateList(t *testing.T) {
 	}
 }
 
+func TestStateListWithID(t *testing.T) {
+	state := testState()
+	statePath := testStateFile(t, state)
+
+	p := testProvider()
+	ui := new(cli.MockUi)
+	c := &StateListCommand{
+		Meta: Meta{
+			testingOverrides: metaOverridesForProvider(p),
+			Ui:               ui,
+		},
+	}
+
+	args := []string{
+		"-state", statePath,
+		"-id", "bar",
+	}
+	if code := c.Run(args); code != 0 {
+		t.Fatalf("bad: %d\n\n%s", code, ui.ErrorWriter.String())
+	}
+
+	// Test that outputs were displayed
+	expected := strings.TrimSpace(testStateListOutput) + "\n"
+	actual := ui.OutputWriter.String()
+	if actual != expected {
+		t.Fatalf("Expected:\n%q\n\nTo equal: %q", actual, expected)
+	}
+}
+
+func TestStateListWithNonExistentID(t *testing.T) {
+	state := testState()
+	statePath := testStateFile(t, state)
+
+	p := testProvider()
+	ui := new(cli.MockUi)
+	c := &StateListCommand{
+		Meta: Meta{
+			testingOverrides: metaOverridesForProvider(p),
+			Ui:               ui,
+		},
+	}
+
+	args := []string{
+		"-state", statePath,
+		"-id", "baz",
+	}
+	if code := c.Run(args); code != 0 {
+		t.Fatalf("bad: %d\n\n%s", code, ui.ErrorWriter.String())
+	}
+
+	// Test that output is empty
+	if ui.OutputWriter != nil {
+		actual := ui.OutputWriter.String()
+		if actual != "" {
+			t.Fatalf("Expected an empty output but got: %q", actual)
+		}
+	}
+}
+
 func TestStateList_backendState(t *testing.T) {
 	// Create a temporary working directory that is empty
 	td := tempDir(t)

website/docs/commands/state/list.html.md

@@ -31,6 +31,7 @@ The command-line flags are all optional. The list of available flags are:
 
 * `-state=path` - Path to the state file. Defaults to "terraform.tfstate".
   Ignored when [remote state](/docs/state/remote.html) is used.
+* `-id=id` - ID of resources to show. Ignored when unset.
 
 ## Example: All Resources
 
@@ -62,3 +63,14 @@ This example will only list resources in the given module:
 $ terraform state list module.elb
 module.elb.aws_elb.main
 ```
+
+## Example: Filtering by ID
+
+This example will only list the resource whose ID is specified on the
+command line. This is useful to find where in your configuration a
+specific resource is located.
+
+```
+$ terraform state list -id=sg-1234abcd
+module.elb.aws_security_group.sg
+```