Is there any straightforward way for Clap to display help when no command is provided?

Question

I'm using the Clap crate for parsing command line parameters. I've defined a subcommand ls that should list files. Clap also defines a help subcommand that displays information about the application and its usage.

If no command is provided, nothing gets displayed at all, but I want the app to display help in that case.

I've tried this code, which looks pretty straightforward, but it doesn't work:

extern crate clap;  use clap::{App, SubCommand};  fn main() {     let mut app = App::new("myapp")         .version("0.0.1")         .about("My first CLI APP")         .subcommand(SubCommand::with_name("ls").about("List anything"));     let matches = app.get_matches();      if let Some(cmd) = matches.subcommand_name() {         match cmd {             "ls" => println!("List something here"),             _ => eprintln!("unknown command"),         }     } else {         app.print_long_help();     } } 

I get an error that app is used after move:

error[E0382]: use of moved value: `app`   --> src/main.rs:18:9    | 10 |     let matches = app.get_matches();    |                   --- value moved here ... 18 |         app.print_long_help();    |         ^^^ value used here after move    |    = note: move occurs because `app` has type `clap::App<'_, '_>`, which does not implement the `Copy` trait 

Reading through the documentation of Clap, I've found that the clap::ArgMatches that's returned in get_matches() has a method usage that returns the string for usage part, but, unfortunately, only this part and nothing else.

Answer 1

Use clap::AppSettings::ArgRequiredElseHelp:

App::new("myprog")     .setting(AppSettings::ArgRequiredElseHelp) 

See also:

• Method call on clap::App moving ownership more than once