No tasks specified. Usage: f parallel 'echo hello' 'echo wor

Error message

No tasks specified. Usage: f parallel 'echo hello' 'echo world' or 'label:command'

What it means

The `f parallel` CLI entry point checks cmd.tasks before parsing labels. An empty argument list cannot mean anything useful, so it bails with a usage hint embedded in the message.

Source

Thrown at src/parallel.rs:452

        .map(|(label, cmd)| Task::new(label, cmd))
        .collect();

    let runner = Arc::new(ParallelRunner::new(tasks, max_jobs, fail_fast));
    let exit_code = runner.run().await;

    if exit_code != 0 {
        std::process::exit(exit_code);
    }

    Ok(())
}

/// CLI entry point for `f parallel`.
pub fn run(cmd: crate::cli::ParallelCommand) -> Result<()> {
    use tokio::runtime::Runtime;

    if cmd.tasks.is_empty() {
        bail!("No tasks specified. Usage: f parallel 'echo hello' 'echo world' or 'label:command'");
    }

    // Parse tasks: either "label:command" or just "command" (auto-labeled)
    let tasks: Vec<(String, String)> = cmd
        .tasks
        .iter()
        .enumerate()
        .map(|(i, t)| {
            if let Some((label, command)) = t.split_once(':') {
                (label.to_string(), command.to_string())
            } else {
                // Auto-generate label from command or use index
                let label = t
                    .split_whitespace()
                    .next()
                    .unwrap_or(&format!("task{}", i + 1))
                    .to_string();
                (label, t.to_string())

View on GitHub (pinned to a747e741ae)

Solutions

Pass at least one task: f parallel 'echo hello' 'echo world'.
Use label:command syntax for named tasks: f parallel build:cargo build.
In scripts, guard against empty argument arrays before invoking f parallel.

Example fix

// before
$ f parallel
// No tasks specified. Usage: ...

// after
$ f parallel 'lint:npm run lint' 'test:npm test'

Defensive patterns

Strategy: validation

Validate before calling

if [ ${#TASKS[@]} -eq 0 ]; then
  echo "usage: f parallel 'cmd1' 'label:cmd2'" >&2
  exit 1
fi
f parallel "${TASKS[@]}"

Prevention

Always quote each task argument so spaces survive shell splitting.
In scripts, build the argument array and bail if it is empty before invoking f parallel.
Use label:command form to keep output attributable to tasks.

When it happens

Trigger: Running `f parallel` with no quoted task arguments, or `f parallel ""` where parsing yields no tasks.

Common situations: Shell scripts building the command from an empty array (word-splitting drops all args); forgetting to quote commands containing spaces so the shell mangles them.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

AI-assisted analysis of nikivdev/code@a747e741ae (2026-09-01). Data as JSON: /api/errors/fc0d2910b434da16. Report an issue: GitHub.