use clap::{App, AppSettings}; fn main() { // You can use AppSettings to change the application level behavior of clap. .setting() function // of App struct takes AppSettings enum as argument. There is also .settings() function which // takes slice of AppSettings enum. You can learn more about AppSettings in the documentation, // which also has examples on each setting. // // This example will only show usage of one AppSettings setting. See documentation for more // information. let matches = App::new("myapp") .setting(AppSettings::SubcommandsNegateReqs) // Negates requirement of parent command. .arg(" 'input file to use'") // Required positional argument called input. This // will be only required if subcommand is not present. .subcommand(App::new("test").about("does some testing")) // if program is invoked with subcommand, you do not // need to specify the argument anymore due to // the AppSettings::SubcommandsNegateReqs setting. .get_matches(); // Calling unwrap() on "input" would not be advised here, because although it's required, // if the user uses a subcommand, those requirements are no longer required. Hence, we should // use some sort of 'if let' construct if let Some(inp) = matches.value_of("input") { println!("The input file is: {}", inp); } match matches.subcommand_name() { Some("test") => println!("The 'test' subcommand was used"), _ => unreachable!(), } }