Crate getopts

source ·
Expand description

Simple getopt alternative.

Construct a vector of options, either by using reqopt, optopt, and optflag or by building them from components yourself, and pass them to getopts, along with a vector of actual arguments (not including argv[0]). You’ll either get a failure code back, or a match. You’ll have to verify whether the amount of ‘free’ arguments in the match is what you expect. Use opt_* accessors to get argument values out of the matches object.

Single-character options are expected to appear on the command line with a single preceding dash; multiple-character options are expected to be proceeded by two dashes. Options that expect an argument accept their argument following either a space or an equals sign. Single-character options don’t require the space.


This crate is on and can be used by adding getopts to the dependencies in your project’s Cargo.toml.

getopts = "0.2"

and this to your crate root:

extern crate getopts;


The following example shows simple command line parsing for an application that requires an input file to be specified, accepts an optional output file name following -o, and accepts both -h and --help as optional flags.

extern crate getopts;
use getopts::Options;
use std::env;

fn do_work(inp: &str, out: Option<String>) {
    println!("{}", inp);
    match out {
        Some(x) => println!("{}", x),
        None => println!("No Output"),

fn print_usage(program: &str, opts: Options) {
    let brief = format!("Usage: {} FILE [options]", program);
    print!("{}", opts.usage(&brief));

fn main() {
    let args: Vec<String> = env::args().collect();
    let program = args[0].clone();

    let mut opts = Options::new();
    opts.optopt("o", "", "set output file name", "NAME");
    opts.optflag("h", "help", "print this help menu");
    let matches = match opts.parse(&args[1..]) {
        Ok(m) => { m }
        Err(f) => { panic!(f.to_string()) }
    if matches.opt_present("h") {
        print_usage(&program, opts);
    let output = matches.opt_str("o");
    let input = if ! {[0].clone()
    } else {
        print_usage(&program, opts);
    do_work(&input, output);


  • The result of checking command line arguments. Contains a vector of matches and a vector of free strings.
  • A description of the options that a program can handle.


  • The type returned when the command line does not conform to the expected format. Use the Debug implementation to output detailed information.
  • Describes whether an option has an argument.
  • Describes how often an option may occur.
  • What parsing style to use when parsing arguments.

Type Aliases

  • The result of parsing a command line with a set of options.