Function simple_command 

pub async fn simple_command<'a, R, V, W, IV, IW, S, E>(
    vars: IV,
    words: IW,
    env: &'a mut E,
) -> Result<BoxFuture<'static, ExitStatus>, S::Error>
where
    IV: Iterator<Item = RedirectOrVarAssig<R, V, W>>,
    IW: Iterator<Item = RedirectOrCmdWord<R, W>>,
    R: RedirectEval<E, Handle = E::FileHandle>,
    R::Error: 'static + Error + From<RedirectionError>,
    W: WordEval<E>,
    W::Error: 'static + Error,
    E: ?Sized + Send + Sync + AsyncIoEnvironment + BuiltinEnvironment<BuiltinName = <E as FunctionEnvironment>::FnName> + ExecutableEnvironment + ExportedVariableEnvironment + FileDescEnvironment + FileDescOpener + FunctionEnvironment<Fn = S> + FunctionFrameEnvironment + SetArgumentsEnvironment + UnsetVariableEnvironment + WorkingDirectoryEnvironment,
    E::Builtin: BuiltinUtility<'a, Vec<W::EvalResult>, EnvRestorer<'a, E>, E>,
    E::Arg: From<W::EvalResult>,
    E::Args: From<VecDeque<E::Arg>>,
    E::FileHandle: Send + Sync + Clone + FileDescWrapper + From<E::OpenedFileHandle>,
    E::FnName: From<W::EvalResult>,
    E::IoHandle: Send + Sync + From<E::FileHandle>,
    E::VarName: Send + Sync + Clone + Borrow<String> + From<V>,
    E::Var: Send + Sync + Clone + Borrow<String> + From<W::EvalResult>,
    S: Spawn<E> + Clone,
    S::Error: From<R::Error> + From<W::Error> + From<CommandError> + From<RedirectionError>,

Spawns a shell command (or function) after applying any redirects and environment variable assignments.