mirror of
https://github.com/clap-rs/clap
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39 lines
1.3 KiB
Rust
39 lines
1.3 KiB
Rust
extern crate clap;
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use clap::{App, Arg};
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fn main() {
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// You can define a function (or a closure) to use as a validator to argument values. The
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// function must accept a String and return Result<(), String> where Err(String) is the message
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// displayed to the user.
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let matches = App::new("myapp")
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// Application logic goes here...
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.arg(
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Arg::with_name("input")
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.help("the input file to use")
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.index(1)
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.required(true)
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// You can pass in a closure, or a function
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.validator(is_png),
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)
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.get_matches();
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// Here we can call .unwrap() because the argument is required.
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println!("The .PNG file is: {}", matches.value_of("input").unwrap());
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}
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fn is_png(val: String) -> Result<(), String> {
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// val is the argument value passed in by the user
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// val has type of String.
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if val.ends_with(".png") {
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Ok(())
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} else {
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// clap automatically adds "error: " to the beginning
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// of the message.
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Err(String::from("the file format must be png."))
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}
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// Of course, you can do more complicated validation as
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// well, but for the simplicity, this example only checks
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// if the value passed in ends with ".png" or not.
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}
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