What causes "accepts %d arg(s), received %d" in spf13/cobra?

Provide exactly n positional arguments.

accepts %d arg(s), received %d

Error message

accepts %d arg(s), received %d

What it means

Returned by ExactArgs(n) when the number of positional arguments is not exactly n. ExactArgs is the strictest of the counting validators — both too few and too many trigger it.

Source

Thrown at args.go:110

		return nil
	}
}

// MaximumNArgs returns an error if there are more than N args.
func MaximumNArgs(n int) PositionalArgs {
	return func(cmd *Command, args []string) error {
		if len(args) > n {
			return fmt.Errorf("accepts at most %d arg(s), received %d", n, len(args))
		}
		return nil
	}
}

// ExactArgs returns an error if there are not exactly n args.
func ExactArgs(n int) PositionalArgs {
	return func(cmd *Command, args []string) error {
		if len(args) != n {
			return fmt.Errorf("accepts %d arg(s), received %d", n, len(args))
		}
		return nil
	}
}

// RangeArgs returns an error if the number of args is not within the expected range.
func RangeArgs(min int, max int) PositionalArgs {
	return func(cmd *Command, args []string) error {
		if len(args) < min || len(args) > max {
			return fmt.Errorf("accepts between %d and %d arg(s), received %d", min, max, len(args))
		}
		return nil
	}
}

// MatchAll allows combining several PositionalArgs to work in concert.
func MatchAll(pargs ...PositionalArgs) PositionalArgs {
	return func(cmd *Command, args []string) error {

View on GitHub (pinned to adbc881390)

Solutions

Provide exactly n positional arguments.
Confirm flags that take values aren't stealing operands (use `=` form: `--flag=val`).
If the real requirement is a range, switch to RangeArgs; if it's a minimum, use MinimumNArgs.

Example fix

// before
cmd.Args = cobra.ExactArgs(2)
// `cmd cp src` -> accepts 2 arg(s), received 1

// after: `cmd cp src dst`

Defensive patterns

Strategy: validation

Validate before calling

// Validate exact arity before Execute for a clearer message
cmd.Args = cobra.ExactArgs(2)
cmd.PreRunE = func(c *cobra.Command, args []string) error {
    if len(args) != 2 { return fmt.Errorf("expected SRC and DST, got %d args", len(args)) }
    return nil
}

Type guard

null

Try / catch

null

Prevention

Use ExactArgs only for fixed-arity commands (cp, mv, rename).
Document operands positionally in Use (e.g. `Use: "cp SRC DST"`).
Switch to RangeArgs if the true arity has any flex.

When it happens

Trigger: Setting `cmd.Args = cobra.ExactArgs(2)` and calling `cmd cp src` (one) or `cmd cp src dst extra` (three). Frequently seen with cp/mv-style commands that demand a fixed operand count.

Common situations: Optional flags consuming an operand, quoting collapsing/expanding arg count, or a command whose arity changed between versions.

Related errors

AI-assisted analysis of spf13/cobra@adbc881390 (2026-08-04). Data as JSON: /data/errors/251c5f47c4a3e562.json. Report an issue: GitHub.