What causes "invalid argument %q for "-%s, --%s" flag: %v" in JanDeDobbeleer/oh-my-posh?

Use a value valid for the flag type: true/false/0/1 for bools, digits for int/float.

invalid argument %q for "-%s, --%s" flag: %v

Error message

invalid argument %q for "-%s, --%s" flag: %v

What it means

Raised when a shorthand's value fails flag.Value.Set during parseShort - the same failure mode as the long form's 'invalid argument' error, but the message shows both the shorthand and the long name. The underlying strconv error from bool/int/float parsing is wrapped as %v.

Source

Thrown at src/cmdflag/cmdflag.go:351

		case len(shorthands) > 2 && shorthands[1] == '=':
			value = shorthands[2:]
			shorthands = ""
		case flag.Value.Type() == boolType:
			value = trueStr
			shorthands = shorthands[1:]
		case len(shorthands) > 1:
			value = shorthands[1:]
			shorthands = ""
		case len(rest) > 0:
			value = rest[0]
			rest = rest[1:]
			shorthands = ""
		default:
			return rest, fmt.Errorf("flag needs an argument: %q in -%s", c, shorthands)
		}

		if err := flag.Value.Set(value); err != nil {
			return rest, fmt.Errorf("invalid argument %q for \"-%s, --%s\" flag: %v", value, flag.Shorthand, flag.Name, err)
		}

		flag.Changed = true
	}

	return rest, nil
}

// usage rendering

// FlagUsages renders the non-hidden flags sorted by name, shorthand column,
// type name after the flag, defaults in parentheses when they differ from
// the zero value, usage aligned in a single column.
func (f *FlagSet) FlagUsages() string {
	lines := make([]string, 0, len(f.order))
	maxlen := 0

	flags := make([]*Flag, len(f.order))

View on GitHub (pinned to 0976794618)

Solutions

Use a value valid for the flag type: true/false/0/1 for bools, digits for int/float.
Inspect the trailing strconv error in the message to see the exact parse failure.
Quote shell values so stray characters don't corrupt them.
If you own the CLI, implement a custom Value whose Set accepts the looser syntax your users expect.

Example fix

// before
args := []string{"-p=8o80"} // invalid argument "8o80" for "-p, --port" flag: strconv.ParseInt: parsing "8o80": invalid syntax
// after
args := []string{"-p=8080"}

Defensive patterns

Strategy: validation

Validate before calling

func validNumeric(s string, base int) bool {
    _, err := strconv.ParseInt(s, base, 64)
    return err == nil
}
// guard before invoking: if !validNumeric(port, 10) { return fmt.Errorf("port %q must be an integer", port) }

Try / catch

if err := cmd.Execute(); err != nil {
    if strings.Contains(err.Error(), "invalid argument") && strings.Contains(err.Error(), "flag:") {
        // message includes value, -short, --long name and strconv cause
        fmt.Fprintf(os.Stderr, "%v\n", err)
        os.Exit(2)
    }
    return err
}

Prevention

Sanitize numeric inputs (strip spaces, units, thousands separators) before passing.
Use only strconv-compatible bool literals: true/false/0/1/t/f/T/F/TRUE/FALSE.
Quote values in shell to prevent hidden characters and glob expansion.
Test script invocations with representative values, not just defaults.

When it happens

Trigger: Parse called with '-fVALUE', '-f=VALUE', or '-f VALUE' where VALUE cannot be parsed by the flag's Value type: e.g. '-p=abc' for an int port flag.

Common situations: Typos in numeric values; bool spellings like 'yes'/'on' that strconv.ParseBool rejects; values with whitespace or units from unquoted shell strings; copy-paste introducing invisible characters or smart quotes.

Related errors

AI-assisted analysis of JanDeDobbeleer/oh-my-posh@0976794618 (2026-08-31). Data as JSON: /api/errors/4fbadf89cd9c25ab. Report an issue: GitHub.