go-task/task · error

unknown shell: %s

Error message

unknown shell: %s

What it means

The `task --completion <shell>` command only supports a fixed set of shells (bash, zsh, fish, powershell). Passing any other value returns this error from Completion. It is a simple argument-validation error listing no supported values in the message.

Source

Thrown at completion.go:37

//go:embed completion/zsh/_task
var completionZsh string

func Completion(completion string) (string, error) {
	// Get the file extension for the selected shell
	switch completion {
	case "bash":
		return completionBash, nil
	case "fish":
		return completionFish, nil
	case "nu", "nushell":
		return completionNu, nil
	case "powershell":
		return completionPowershell, nil
	case "zsh":
		return completionZsh, nil
	default:
		return "", fmt.Errorf("unknown shell: %s", completion)
	}
}

View on GitHub (pinned to 385e5ad92a)

Solutions

1. Use one of the supported values: bash, zsh, fish, powershell (exact lowercase spelling)
2. Check `task --help` for the exact completion subcommand syntax for your installed version
3. For unsupported shells, generate the closest supported completion and adapt it manually

Example fix

# before
task --completion sh
# after
task --completion bash

var validShells = map[string]bool{"bash":true,"zsh":true,"fish":true,"powershell":true}
if !validShells[shell] {
  return fmt.Errorf("unsupported shell %q; use bash, zsh, fish or powershell", shell)
}

out, err := exec.Command("task", "--completion", shell).Output()
if err != nil {
  // fall back to bash completion or show supported shells
}

When it happens

Trigger: Running `task --completion <value>` where <value> is not exactly one of the supported shell names handled by the switch in Completion.

Common situations: Typo like `--completion bash4`, using `sh`, `fish`-variant names or capitalized values (`Bash`), or copying an example from another tool (e.g. `--completion powershell-core`).

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• task: You can't set both --download and --offline flags
• task: You can't set both --download and --clear-cache flags
• task: You can't set both --global and --dir
• task: You can't set --output-group-begin without --output=gr
• task: You can't set --output-group-end without --output=grou

AI-assisted analysis of go-task/task@385e5ad92a (2026-09-05). Data as JSON: /api/errors/cfd6bb0d89c2b46e. Report an issue: GitHub.