What causes "Expected a single argument: NAME." in hashicorp/terraform?

Provide the workspace name: 'terraform workspace select NAME'.

Expected a single argument: NAME.

Error message

Expected a single argument: NAME.

What it means

Returned by ParseWorkspaceSelect (workspace_select.go:45) when, after flag parsing, zero positional arguments are present — i.e. 'terraform workspace select' was run with no NAME. Exactly one workspace name is required to switch to it.

Source

Thrown at internal/command/arguments/workspace_select.go:45

func ParseWorkspaceSelect(args []string) (*WorkspaceSelect, tfdiags.Diagnostics) {
	var diags tfdiags.Diagnostics

	var orCreate bool
	cmdFlags := defaultFlagSet("workspace select")
	cmdFlags.BoolVar(&orCreate, "or-create", false, "create workspace if it does not exist")
	if err := cmdFlags.Parse(args); err != nil {
		diags = diags.Append(tfdiags.Sourceless(
			tfdiags.Error,
			"Failed to parse command-line flags",
			err.Error(),
		))
	}

	// `workspace select` takes only one positional argument: workspace name.
	args = cmdFlags.Args()
	var name string
	if len(args) == 0 {
		diags = diags.Append(errors.New("Expected a single argument: NAME.")) // Recreating pre-existing error from command package
	} else {
		// Obtain and validate name argument.
		name = args[0]
		if !ValidWorkspaceName(name) {
			diags = diags.Append(fmt.Errorf(EnvInvalidName, name))
		}

		// Checking for extra arguments here, not with a len != 1 check above, allows the name to be returned
		args = args[1:]
		if len(args) != 0 {
			diags = diags.Append(errors.New("Expected a single argument: NAME."))
		}
	}

	return &WorkspaceSelect{
		Workspace: Workspace{ViewType: ViewHuman},
		OrCreate:  orCreate,
		Name:      name,

View on GitHub (pinned to c9def3e214)

Solutions

Provide the workspace name: 'terraform workspace select NAME'.
Run 'terraform workspace list' to see available names.
Use 'terraform workspace select -or-create=NAME' if you want create-if-missing semantics.

Example fix

# before
$ terraform workspace select
# after
$ terraform workspace select prod

Defensive patterns

Strategy: validation

Validate before calling

// Ensure a name is present for 'workspace select'.
func validateSelectName(args []string) error {
    if len(args) == 0 {
        return errors.New("workspace select requires a NAME argument")
    }
    return nil
}

Prevention

Always pass a workspace name to 'terraform workspace select'.
List workspaces first if unsure of available names.
Use -or-create if you want create-if-missing behavior.

When it happens

Trigger: Line 43-45: cmdFlags.Args() returns len(args)==0 -> the error is appended; Name stays empty.

Common situations: Running 'terraform workspace select' bare; an empty variable expansion in a script; mistaking it for 'terraform workspace list'.

Related errors

AI-assisted analysis of hashicorp/terraform@c9def3e214 (2026-08-07). Data as JSON: /api/errors/02c3397a0952c8b1. Report an issue: GitHub.