| #[macro_use] |
| extern crate clap; |
| |
| use clap::App; |
| |
| fn main() { |
| // You can use some convenience macros provided by clap to get typed values, so long as the |
| // type you specify implements std::str::FromStr |
| // |
| // This works for both single, and multiple values (multiple values returns a Vec<T>) |
| // |
| // There are also two ways in which to get types, those where failures cause the program to exit |
| // with an error and usage string, and those which return a Result<T,String> or Result<Vec<T>,String> |
| // respectively. Both methods support single and multiple values. |
| // |
| // The macro which returns a Result allows you decide what to do upon a failure, exit, provide a |
| // default value, etc. You have control. But it also means you have to write the code or boiler plate |
| // to handle those instances. |
| // |
| // That is why the second method exists, so you can simply get a T or Vec<T> back, or be sure the |
| // program will exit gracefully. The catch is, the second method should *only* be used on required |
| // arguments, because if the argument isn't found, it exits. Just FYI ;) |
| // |
| // The following example shows both methods. |
| // |
| // **NOTE:** to use the macros, you must include #[macro_use] just above the 'extern crate clap;' |
| // declaration in your crate root. |
| let matches = App::new("myapp") |
| // Create two arguments, a required positional which accepts multiple values |
| // and an optional '-l value' |
| .args_from_usage( |
| "<seq>... 'A sequence of whole positive numbers, i.e. 20 25 30' |
| -l [len] 'A length to use, defaults to 10 when omitted'") |
| .get_matches(); |
| |
| // Here we get a value of type u32 from our optional -l argument. |
| // If the value provided to len failes to parse, we default to 10 |
| // |
| // Using other methods such as unwrap_or_else(|e| println!("{}",e)) |
| // are possible too. |
| let len = value_t!(matches, "len", u32).unwrap_or(10); |
| |
| println!("len ({}) + 2 = {}", len, len + 2); |
| |
| // This code loops through all the values provided to "seq" and adds 2 |
| // If seq fails to parse, the program exits, you don't have an option |
| for v in values_t!(matches, "seq", u32).unwrap_or_else(|e| e.exit()) { |
| println!("Sequence part {} + 2: {}", v, v + 2); |
| } |
| } |