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extern crate clap;
use clap::{App, Arg};
fn main() {
// If you have arguments of specific values you want to test for, you can use the
// .possible_values() method of Arg
// This allows you specify the valid values for that argument. If the user does not use one of
// those specific values, they will receive a graceful exit with error message informing them
// of the mistake, and what the possible valid values are
// For this example, assume you want one positional argument of either "fast" or "slow"
// i.e. the only possible ways to run the program are "myprog fast" or "myprog slow"
let matches = App::new("myapp").about("does awesome things")
.help("What mode to run the program in")
.possible_values(&["fast", "slow"])
// Note, it's safe to call unwrap() because the arg is required
match matches.value_of("MODE").unwrap() {
"fast" => {
// Do fast things...
"slow" => {
// Do slow things...
_ => unreachable!()
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