Argh

Argh is an opinionated Derive-based argument parser optimized for code size

Derive-based argument parsing optimized for code size and conformance
to the Fuchsia commandline tools specification

The public API of this library consists primarily of the FromArgs
derive and the from_env function, which can be used to produce
a top-level FromArgs type from the current program's commandline
arguments.

Basic Example

rust
use argh::FromArgs;

#[derive(FromArgs)]
/// Reach new heights.
struct GoUp {
    /// whether or not to jump
    #[argh(switch, short = 'j')]
    jump: bool,

    /// how high to go
    #[argh(option)]
    height: usize,

    /// an optional nickname for the pilot
    #[argh(option)]
    pilot_nickname: Option<String>,
}

fn main() {
    let up: GoUp = argh::from_env();
}

./some_bin --help will then output the following:

Usage: cmdname [-j] --height <height> [--pilot-nickname <pilot-nickname>]

Reach new heights.

Options:
  -j, --jump        whether or not to jump
  --height          how high to go
  --pilot-nickname  an optional nickname for the pilot
  --help, help      display usage information

The resulting program can then be used in any of these ways:

./some_bin --height 5
./some_bin -j --height 5
./some_bin --jump --height 5 --pilot-nickname Wes

Switches, like jump, are optional and will be set to true if provided.

Options, like height and pilot_nickname, can be either required,
optional, or repeating, depending on whether they are contained in an
Option or a Vec. Default values can be provided using the
#[argh(default = "<your_code_here>")] attribute, and in this case an
option is treated as optional.

rust
use argh::FromArgs;

fn default_height() -> usize {
    5
}

#[derive(FromArgs)]
/// Reach new heights.
struct GoUp {
    /// an optional nickname for the pilot
    #[argh(option)]
    pilot_nickname: Option<String>,

    /// an optional height
    #[argh(option, default = "default_height()")]
    height: usize,

    /// an optional direction which is "up" by default
    #[argh(option, default = "String::from(\"only up\")")]
    direction: String,
}

fn main() {
    let up: GoUp = argh::from_env();
}

Custom option types can be deserialized so long as they implement the
FromArgValue trait (automatically implemented for all FromStr types).
If more customized parsing is required, you can supply a custom
fn(&str) -> Result<T, String> using the from_str_fn attribute:

rust
use argh::FromArgs;

#[derive(FromArgs)]
/// Goofy thing.
struct FiveStruct {
    /// always five
    #[argh(option, from_str_fn(always_five))]
    five: usize,
}

fn always_five(_value: &str) -> Result<usize, String> {
    Ok(5)
}

Positional arguments can be declared using #[argh(positional)].
These arguments will be parsed in order of their declaration in
the structure:

rust
use argh::FromArgs;

#[derive(FromArgs, PartialEq, Debug)]
/// A command with positional arguments.
struct WithPositional {
    #[argh(positional)]
    first: String,
}

The last positional argument may include a default, or be wrapped in
Option or Vec to indicate an optional or repeating positional argument.

Subcommands are also supported. To use a subcommand, declare a separate
FromArgs type for each subcommand as well as an enum that cases
over each command:

rust
use argh::FromArgs;

#[derive(FromArgs, PartialEq, Debug)]
/// Top-level command.
struct TopLevel {
    #[argh(subcommand)]
    nested: MySubCommandEnum,
}

#[derive(FromArgs, PartialEq, Debug)]
#[argh(subcommand)]
enum MySubCommandEnum {
    One(SubCommandOne),
    Two(SubCommandTwo),
}

#[derive(FromArgs, PartialEq, Debug)]
/// First subcommand.
#[argh(subcommand, name = "one")]
struct SubCommandOne {
    #[argh(option)]
    /// how many x
    x: usize,
}

#[derive(FromArgs, PartialEq, Debug)]
/// Second subcommand.
#[argh(subcommand, name = "two", short = 't')]
struct SubCommandTwo {
    #[argh(switch)]
    /// whether to fooey
    fooey: bool,
}

Advanced Description

You can define a complex help output that includes an Examples section.
Use a {command_name} placeholder.

rust
#[derive(FromArgs, Debug)]
#[argh(
    description = "{command_name} is a tool to reach new heights.\n\n\
    Start exploring new heights:\n\n\
    \u{00A0} {command_name} --height 5 jump\n\
    ",
    example = "\
    {command_name} --height 5\n\
    {command_name} --height 5 j\n\
    {command_name} --height 5 --pilot-nickname Wes jump"
)]
pub struct CliArgs {
    /// how high to go
    #[argh(option)]
    height: usize,
    /// an optional nickname for the pilot
    #[argh(option)]
    pilot_nickname: Option<String>,
    /// command to execute
    #[argh(subcommand)]
    pub command: Command,
}

Output:

Usage: goup --height <height> [--pilot-nickname <pilot-nickname>] <command> [<args>]

goup is a tool to reach new heights.

Start exploring new heights:

  goup --height 5 jump

Options:
  --height          how high to go
  --pilot-nickname  an optional nickname for the pilot
  --help, help      display usage information

Commands:
  jump  j           whether or not to jump

Examples:
  goup --height 5
  goup --height 5 j
  goup --height 5 --pilot-nickname Wes jump