A simple and consistent derive-based command line argument parsing, in the same genre as Clap-derive. It currently supports

• Command line parsing
• Help

Generally speaking this is intended to make CLI parsing simple by virtue of being simple and consistent, rather than poweruser-optimized keypress-minimizing parsing.

This attempts to support parsing arbitrarily complex command line arguments. Like with Serde, you can combine structs, vecs, enums in any way you want. Just because you can doesn't mean you should.

A definition like:

#[derive(Aargvark)]
struct RestartArgs {
    message: String,
}

#[derive(Aargvark)]
struct StopArgs {
    message: String,
    force: bool,
}

#[derive(Aargvark)]
#[vark(break_help)]
enum Command {
    Start,
    Restart(RestartArgs),
    Stop(StopArgs),
}

#[derive(Aargvark)]
struct Args {
    debug: Option<()>,
    config: Option<PathBuf>,
    server_name: String,
    command: Command,
}

let args = aargvark::vark::<Args>();

Produces this output:

$ ; (The real thing is colored too)
$ ultrathon -h
Usage: ultrathon SERVER-NAME COMMAND [ ...FLAGS]

    This is an example of a command, with explanations taken from docstrings.

    SERVER-NAME: <STRING>               Name of server in config to run command on
    COMMAND: COMMAND
    [--debug]                           Enable verbose log output
    [--config <PATH>]                   Path to servers config JSON

COMMAND: start | restart | stop

    start ...
    restart ...
    stop ...

$ ultrathon bootleg-server stop -h
Usage: ultrathon bootleg-server stop MESSAGE FORCE

    Stop all tasks, then stop the server.

    MESSAGE: <STRING>                   Message to send users before stopping.
    [--force]                           Force the server to stop even if there are pending tasks.

Why or why not

Why this and not Clap?

• It has a super-simple interface (just #[derive(Aargvark)] on any enum/structure)
• This parses more complex data types, like vectors of sub-structures, or enums
• It's more consistent

Why not this?

• It's newer, with fewer features and limited community ecosystem, extensions
• Some command line parsing conventions were discarded in order to simplify and maintain self-similarity. A lot of command line conventions are inconsistent or break down as you nest things, after all.
• Quirky CLI parsing generally isn't supported.

Conventions and usage

To add it to your project, run

cargo add aargvark

To parse command line arguments

1. Define the data type you want to parse them into, like

   /// General description for the command.
   #[derive(Aargvark)]
   struct MyArgs {
     /// Field documentation.
     velociraptor: String,
     #[vark(flag = "-d", flag = "--deadly")]
     deadly: bool,
     color_pattern: Option<ColorPattern>,
   }
   

2. Vark it

   let args = vark::<MyArgs>();
   

Non-optional fields become positional arguments unless you give them a flag with #[vark(flag = "--flag")]. Optional fields become optional (--long) arguments. If you want a bool flag that's enabled if the flag is specified (i.e. doesn't take a value), use Option<()>.

You can derive structs, enums, and tuples, and there are implementations for Vec, HashSet, Map with FromString keys and values as K=V arguments, most Ip and SocketAddr types, and PathBuf built in.

Some additional wrappers are provided for automatically loading (and parsing) files:

• AargvarkFile<T>
• AargvarkJson<T> requires feature serde_json
• AargvarkYaml<T> requires feature serde_yaml

To parse your own types, implement AargvarkTrait, or if your type takes a single string argument you can implement AargvarkFromStr which is slightly simpler.

Advanced usage

• Sequences, plural fields, Vecs

  Sequence elements are space separated. The way sequence parsing works is it attempts to parse as many elements as possible. When parsing one element fails, it rewinds to after it parsed the last successful element and proceeds from the next field after the sequence.

• Use flags, replace flags, and add additional flags

  Add ex: #[vark(flag="--target-machine", flag="-tm")] to a field.

  If the field was optional, this will replace the default flag. If the field was non-optional, this will make it require a flag instead of being positional.

• Rename enum variant keys

  Add ex: #[vark(name="my-variant")] to a variant.

  This changes the command line key used to select a variant.

• Prevent recursion in help

  Add #[vark(break_help)] to a type, field, or variant to prevent recursing into any of the children when displaying help. This is useful for subcommand enums - attach this to the enum and it will list the variants but not the variants' arguments (unless you do -h after specifying one on the command line).

• Change the help placeholder string

  Add #[vark(placeholder="TARGET-MACHINE")] to a type, field, or variant.

  This is the capitalized text (like XYZ) after an option that basically means "see XYZ section for more details"