command/fmt: Accept optional directory argument

So that you can operate on files in a directory other than your current
working directory.

command/fmt.go

@@ -34,13 +34,19 @@ func (c *FmtCommand) Run(args []string) int {
 	}
 
 	args = cmdFlags.Args()
-	if len(args) > 0 {
+	if len(args) > 1 {
-		c.Ui.Error("The fmt command expects no arguments.")
+		c.Ui.Error("The fmt command expects at most one argument.")
 		cmdFlags.Usage()
 		return 1
 	}
 
-	dir := "."
+	var dir string
+	if len(args) == 0 {
+		dir = "."
+	} else {
+		dir = args[0]
+	}
+
 	output := &cli.UiWriter{Ui: c.Ui}
 	err := fmtcmd.Run([]string{dir}, []string{fileExtension}, nil, output, c.opts)
 	if err != nil {
@@ -53,10 +59,11 @@ func (c *FmtCommand) Run(args []string) int {
 
 func (c *FmtCommand) Help() string {
 	helpText := `
-Usage: terraform fmt [options]
+Usage: terraform fmt [options] [DIR]
 
-	Rewrites all Terraform configuration files in the current working
+	Rewrites all Terraform configuration files to a canonical format.
-	directory to a canonical format.
+
+	If DIR is not specified then the current working directory will be used.
 
 Options:
 

command/fmt_test.go

@@ -47,12 +47,15 @@ func TestFmt_tooManyArgs(t *testing.T) {
 		},
 	}
 
-	args := []string{"bad"}
+	args := []string{
+		"one",
+		"two",
+	}
 	if code := c.Run(args); code != 1 {
 		t.Fatalf("wrong exit code. errors: \n%s", ui.ErrorWriter.String())
 	}
 
-	expected := "The fmt command expects no arguments."
+	expected := "The fmt command expects at most one argument."
 	if actual := ui.ErrorWriter.String(); !strings.Contains(actual, expected) {
 		t.Fatalf("expected:\n%s\n\nto include: %q", actual, expected)
 	}
@@ -94,6 +97,32 @@ func TestFmt_workingDirectory(t *testing.T) {
 	}
 }
 
+func TestFmt_directoryArg(t *testing.T) {
+	tempDir, err := fmtFixtureWriteDir()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	defer os.RemoveAll(tempDir)
+
+	ui := new(cli.MockUi)
+	c := &FmtCommand{
+		Meta: Meta{
+			ContextOpts: testCtxConfig(testProvider()),
+			Ui:          ui,
+		},
+	}
+
+	args := []string{tempDir}
+	if code := c.Run(args); code != 0 {
+		t.Fatalf("wrong exit code. errors: \n%s", ui.ErrorWriter.String())
+	}
+
+	expected := fmt.Sprintf("%s\n", filepath.Join(tempDir, fmtFixture.filename))
+	if actual := ui.OutputWriter.String(); actual != expected {
+		t.Fatalf("got: %q\nexpected: %q", actual, expected)
+	}
+}
+
 var fmtFixture = struct {
 	filename      string
 	input, golden []byte

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

@@ -15,7 +15,9 @@ to a canonical format and style.
 
 Usage: `terraform fmt [options] [DIR]`
 
-`fmt` scans the current directory for configuration files.
+By default, `fmt` scans the current directory for configuration files. If
+the `dir` argument is provided then it will scan that given directory
+instead.
 
 The command-line flags are all optional. The list of available flags are: