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extern crate clap;
use clap::{App, Arg};
fn main() {
// There are two ways in which to get a default value, one is to use claps Arg::default_value
// method, and the other is to use Rust's built in Option::unwrap_or method.
//
// I'll demo both here.
//
// First, we'll use clap's Arg::default_value with an "INPUT" file.
let matches = App::new("myapp").about("does awesome things")
.arg(Arg::with_name("INPUT")
.help("The input file to use") // Note, we don't need to specify
// anything like, "Defaults to..."
// because clap will automatically
// generate that for us, and place
// it in the help text
.default_value("input.txt")
.index(1))
// Next we'll use the Option::unwrap_or method on this "CONFIG" option
.arg(Arg::with_name("CONFIG")
// Note that we have to manually include some verbiage to the user
// telling them what the default will be.
.help("The config file to use (default is \"config.json\")")
.short("c")
.takes_value(true))
.get_matches();
// It's safe to call unwrap because the value with either be what the user input at runtime
// or "input.txt"
let input = matches.value_of("INPUT").unwrap();
// Using Option::unwrap_or we get the same affect, but without the added help text injection
let config_file = matches.value_of("CONFIG").unwrap_or("config.json");
println!("The input file is: {}", input);
println!("The config file is: {}", config_file);
}
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