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#156 in Command-line interface

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github crates.io docs.rs build status

Define a simple command-line parser through a declarative macro.

This is not intended to be a complete command-line parser library. Instead this can be used as an alternative quick-and-dirty approach that can be cheaply incorporated into a tool.

For a more complete command-line parsing library, use clap.

We provide:

  • A dependency-free command-line parsing framework using declarative macros.
  • A flexible mechanism for parsing.
  • Formatting of decent looking help messages.

We do not provide:

  • As-close-to correct line wrapping with wide unicode characters as possible (see textwrap).
  • Built-in complex command structures like subcommands (see the subcommands example for how this can be accomplished).

For how to use, see the documentation of argwerk::define and argwerk::args.


Initially when you're adding arguments to your program you can use argwerk::args. This allows for easily parsing out a handful of optional parameters.

This example is available as simple:

cargo run --example simple -- --limit 20
let args = argwerk::args! {
    /// A simple tool.
    "tool [-h]" {
        help: bool,
        limit: usize = 10,
    /// The limit of the operation. (default: 10).
    ["-l" | "--limit", int] => {
        limit = str::parse(&int)?;
    /// Print this help.
    ["-h" | "--help"] => {
        println!("{}", HELP);
        help = true;

if args.help {
    return Ok(());


After a while you might want to graduate to defining a named struct containing the arguments. This can be useful if you want to pass the arguments around.

This example is available as tour:

cargo run --example tour -- --help
use std::ffi::OsString;

argwerk::define! {
    /// A command touring the capabilities of argwerk.
    #[usage = "tour [-h]"]
    struct Args {
        help: bool,
        #[required = "--file must be specified"]
        file: String,
        input: Option<String>,
        limit: usize = 10,
        positional: Option<(String, Option<String>)>,
        raw: Option<OsString>,
        rest: Vec<String>,
    /// Prints the help.
    /// This includes:
    ///    * All the available switches.
    ///    * All the available positional arguments.
    ///    * Whatever else the developer decided to put in here! We even support wrapping comments which are overly long.
    ["-h" | "--help"] => {
        println!("{}", Args::help());
        help = true;
    /// Limit the number of things by <n> (default: 10).
    ["--limit" | "-l", n] => {
        limit = str::parse(&n)?;
    /// Write to the file specified by <path>.
    ["--file", path] if !file.is_some() => {
        file = Some(path);
    /// Read from the specified input.
    ["--input", #[option] path] => {
        input = path;
    /// A really long argument that exceeds usage limit and forces the documentation to wrap around with newlines.
    ["--really-really-really-long-argument", thing] => {
    /// A raw argument that passes whatever was passed in from the operating system.
    ["--raw", #[os] arg] => {
        raw = Some(arg);
    /// Takes argument at <foo> and <bar>.
    ///    * This is an indented message. The first alphanumeric character determines the indentation to use.
    [foo, #[option] bar, #[rest] args] if positional.is_none() => {
        positional = Some((foo, bar));
        rest = args;

// Note: we're using `parse` here instead of `args` since it works better
// with the example.
let args = Args::parse(vec!["--file", "foo.txt", "--input", "-"])?;


Time and size compared to other projects

argwerk aims to be a lightweight dependency that is fast to compile. This is how it stacks up to other projects in that regard.

The following summary was generated from the projects found here.

project cold build (release) rebuild* (release) size (release)
argh** 5.142723s (4.849361s) 416.9594ms (468.7003ms) 297k (180k)
argwerk 1.443709s (1.2971457s) 403.0641ms (514.036ms) 265k (185k)
clap*** 11.9863223s (13.1338799s) 551.407ms (807.8939ms) 2188k (750k)

*: rebuild was triggered by adding a single newline to main.rs.
**: argh 0.1.4 including 11 dependencies.
***: clap 3.0.0-beta.2 including 32 dependencies.

You can try and build it yourself with:

cargo run --manifest-path tools/builder/Cargo.toml

No runtime deps