Argparse

The rust-argparse is command-line parsing module for rust. It's inspired by python's argparse module.

Features:

• Supports standard (GNU) option conventions
• Properly typed values
• Automatically generated help and usage messages

Example

The following code is a simple Rust program with command-line arguments:

extern crate argparse;

use std::os;

use argparse::{ArgumentParser, StoreTrue, Store};

fn main() {
    let mut verbose = false;
    let mut name = "World".to_string();

    let mut ap = ArgumentParser::new();
    ap.set_description("Greet somebody.");
    ap.refer(&mut verbose)
        .add_option(["-v", "--verbose"], box StoreTrue,
        "Be verbose");
    ap.refer(&mut name)
        .add_option(["--name"], box Store::<String>,
        "Name for the greeting");
    match ap.parse_args() {
        Ok(()) => {}
        Err(x) => {
            os::set_exit_status(x);
            return;
        }
    }

    if verbose {
        println!("name is {}", name);
    }
    println!("Hello {}!", name);
}

Assuming the Rust code above is saved into a file greeting.rs, let's see what we have now:

$ rustc greeting.rs
$ ./greeting -h
Usage: ./greeting [OPTIONS]

Greet somebody.

optional arguments:
 -h, --help  show this help message and exit
 -v, --verbose
             Be verbose
 --name NAME Name for the greeting
$ ./greeting
Hello World!
$ ./greeting --name Bob
Hello Bob!
$ ./greeting -v --name Alice
name is Alice
Hello Alice!

Basic Workflow

Create ArgumentParser

The argument parser is created empty and is built incrementally. So we create and immutable variable:

extern crate argparse;
use argparse::ArgumentParser;

let mut parser = ArgumentParser::new();

Customize

There are optional customization methods. The most important one is:

parser.set_description("My command-line utility")

The descripion is rewrapped to fit 80 column string nicely. Just like option descriptions.

Add Options

The refer method creates a cell variable, which the result will be written to:

let mut verbose = false; parser.refer(&mut verbose);

Next we add an options which control the variable: For example:

parser.refer(&mut verbose)
    .add_option(["-v", "--verbose"], box StoreTrue,
                "Be verbose");

You made add multiple options for the same variable:

parser.refer(&mut verbose)
    .add_option(["-v", "--verbose"], box StoreTrue,
                "Be verbose")
    .add_option(["-q", "--quiet"], box StoreFalse,
                "Be verbose");

Similarly positional arguments are added:

let mut command = String;
parser.refer(&mut command)
    .add_argument("command", box Store::<String>,
                  "Command to run");

Organizing Options

It's often useful to organize options into some kind of structure. You can easily borrow variables from the structure into option parser. For example:

struct Options {
    verbose: bool,
}
...
let mut options = Options { verbose: false }
parser.refer(&mut options.verbose)
    .add_option(["-v"], box StoreTrue,
                "Be verbose");

Parsing Arguments

All the complex work is done in parser.parser_args(), however, because no exit function exists in rust, some more lines of code needed to check the result:

match parser.parse_args() {
    Ok(()) =>  {}
    Err(x) => {
        os::set_exit_status(x);
        return;
    }
}

ArgumentParser Methods

parser.refer<T>(&mut self, var: &mut T) -> Ref

Attach the variable to argument parser. The options are added to the returned Ref object and modify a variable passed to the method.

parser.set_description(descr: &str)

Set description that is at the top of help message.

parser.stop_on_first_argument(val: bool)

If called with true. Parser will stop searching for options when first non-option (the one doesn't start with -) argument is encountered. This is useful if you want to parse following options with another argparser or external program.

parser.print_usage(writer: Writer)

Prints usage string to stderr.

parser.print_help(writer: Writer)

Writes help to writer, used by --help option internally.

parser.parse_args()

Method that does all the dirty work.

Variable Reference Methods

The argparse::Ref object is returned from parser.refer(). The following methods are used to add and customize arguments:

option.add_option(names: &[&str], action: box TypedAction, help: &str)

Add an option. All items in names should be either in format -X or --long-option (i.e. one dash and one char or two dashes and long name). How this option will be interpreted and whether it will have an argument dependes on the action. See below list of actions.

option.add_argument(name: &str, action: box TypedAction, help: &str)

Add a positional argument

option.metavar(var: &str)

A name of the argument in usage messages (for options having argument).

option.envvar(var: &str)

A name of the environment variable to get option value from. The value would be parsed with FromStr::from_str, just like an option having Store action.

Actions

The following actions are available out of the box. They may be used in either add_option or add_argument:

Store

An option has single argument. Stores a value from command-line in a variable. Any type that has FromStr trait implemented may be used. This action must be specified with box Store::<TYPE> syntax, because of limitation of rust type deriving algorithm. (Known types to work are all integer and floating types, str and path).

StoreConst(value)

An option has no arguments. Store a hard-coded value into variable, when specified. Any type may be used.

StoreTrue

Stores boolean true value in a variable. (shortcut for StoreConst(true))

StoreFalse

Stores boolean false value in a variable. (shortcut for StoreConst(false))

IncrBy(num)

An option has no arguments. Increments the value stored in a variable by a value num. Any type which has Add trait may be used.

DecrBy(nym)

Decrements the value stored in a variable by a value num. Any type which has Add trait may be used.

Collect

When used for an --option, requires single argument. When used for a positional argument consumes all remaining arguments. Parsed options are added to the list. I.e. a box List::<int> action requires a Vec<int> variable. Parses arguments using FromStr trait.

List

When used for positional argument, works the same as List. When used as an option, consumes all remaining arguments.

Note the usage of List is strongly discouraged, because of complex rules below. Use Collect and positional options if possible. But usage of List action may be useful if you need shell expansion of anything other than last positional argument.

Let's learn rules by example. For the next options:

ap.refer(&mut lst1).add_option(["-X", "--xx"], box List::<int>, "List1");
ap.refer(&mut lst2).add_argument("yy", box List::<int>, "List2");

The following command line:

./run 1 2 3 -X 4 5 6

Will return [1, 2, 3] in the lst1 and the [4,5,6] in the lst2.

Note that using when using = or equivalent short option mode, the 'consume all' mode is not enabled. I.e. in the following command-line:

./run 1 2 -X3 4 --xx=5 6

The lst1 has [3, 5] and lst2 has [1, 2, 4, 6]. The argument consuming also stops on -- or the next option:

./run: -X 1 2 3 -- 4 5 6
./run: -X 1 2 --xx=3 4 5 6

Both of the above parse [4, 5, 6] as lst1 and the [1, 2, 3] as the lst2.