structopt 0.2.18

Parse command line argument by defining a struct.

StructOpt Build status

Parse command line argument by defining a struct. It combines clap with custom derive.


Find it on You can also check the examples and the changelog.


Add structopt to your dependencies of your Cargo.toml:

structopt = "0.2"

And then, in your rust file:

extern crate structopt;

use std::path::PathBuf;
use structopt::StructOpt;

/// A basic example
#[derive(StructOpt, Debug)]
#[structopt(name = "basic")]
struct Opt {
    // A flag, true if used in the command line. Note doc comment will
    // be used for the help message of the flag.
    /// Activate debug mode
    #[structopt(short = "d", long = "debug")]
    debug: bool,

    // The number of occurrences of the `v/verbose` flag
    /// Verbose mode (-v, -vv, -vvv, etc.)
    #[structopt(short = "v", long = "verbose", parse(from_occurrences))]
    verbose: u8,

    /// Set speed
    #[structopt(short = "s", long = "speed", default_value = "42")]
    speed: f64,

    /// Output file
    #[structopt(short = "o", long = "output", parse(from_os_str))]
    output: PathBuf,

    /// Number of cars
    #[structopt(short = "c", long = "nb-cars")]
    nb_cars: Option<i32>,

    /// admin_level to consider
    #[structopt(short = "l", long = "level")]
    level: Vec<String>,

    /// Files to process
    #[structopt(name = "FILE", parse(from_os_str))]
    files: Vec<PathBuf>,

fn main() {
    let opt = Opt::from_args();
    println!("{:?}", opt);

Using this example:

$ ./basic
error: The following required arguments were not provided:
    --output <output>

    basic --output <output> --speed <speed>

For more information try --help
$ ./basic --help
basic 0.2.0
Guillaume Pinot <>
A basic example

    basic [FLAGS] [OPTIONS] --output <output> [--] [FILE]...

    -d, --debug      Activate debug mode
    -h, --help       Prints help information
    -V, --version    Prints version information
    -v, --verbose    Verbose mode

    -c, --nb-cars <nb_cars>   Number of cars
    -l, --level <level>...    admin_level to consider
    -o, --output <output>     Output file
    -s, --speed <speed>       Set speed [default: 42]

    <FILE>...    Files to process
$ ./basic -o foo.txt
Opt { debug: false, verbose: 0, speed: 42, output: "foo.txt", car: None, level: [], files: [] }
$ ./basic -o foo.txt -dvvvs 1337 -l alice -l bob --nb-cars 4 bar.txt baz.txt
Opt { debug: true, verbose: 3, speed: 1337, output: "foo.txt", nb_cars: Some(4), level: ["alice", "bob"], files: ["bar.txt", "baz.txt"] }

StructOpt rustc version policy

  • Minimum rustc version modification must be specified in the changelog and in the travis configuration.
  • Contributors can increment minimum rustc version without any justification if the new version is required by the latest version of one of StructOpt's dependencies (cargo update will not fail on StructOpt).
  • Contributors can increment minimum rustc version if the library user experience is improved.


I use docopt since a long time (pre rust 1.0). I really like the fact that you have a structure with the parsed argument: no need to convert String to f64, no useless unwrap. But on the other hand, I don't like to write by hand the usage string. That's like going back to the golden age of WYSIWYG editors. Field naming is also a bit artificial.

Today, the new standard to read command line arguments in Rust is clap. This library is so feature full! But I think there is one downside: even if you can validate argument and expressing that an argument is required, you still need to transform something looking like a hashmap of string vectors to something useful for your application.

Now, there is stable custom derive. Thus I can add to clap the automatic conversion that I miss. Here is the result.


Licensed under either of

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.