Monthly Downloads: 4,309
Programming language: Elixir
License: MIT License

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A command line arguments parsing library for Elixir.

It's aim is to take off the maximum possible amount of manual argument handling. The intended use case is to configure Optimus parser, run it against the command line and then do nothing but take completely validated ready to use values.

The library was strongly inspired by the awesome clap.rs library. Optimus does not generally follow its design, but it tries to follow the idea of zero manual manipulation with the values after the parser has returned them.


Add optimus to your list of dependencies in mix.exs:

def deps do
  [{:optimus, "~> 0.1.0"}]


Let's configure a CLI interface to an imaginary utility which reads data from a file of the following format:

# timestamp, value
1481729245, 12.0
1481729245, 13.0
1481729246, 11.1

and outputs some statistic metrics of the values. It also has a subcommand which validates the source file integrity.

defmodule Statcalc do
  def main(argv) do
      name: "statcalc",
      description: "Statistic metrics calculator",
      version: "1.2.3",
      author: "John Smith [email protected]",
      about: "Utility for calculating statistic metrics of values read from a file for a certain period of time",
      allow_unknown_args: false,
      parse_double_dash: true,
      args: [
        infile: [
          value_name: "INPUT_FILE",
          help: "File with raw data",
          required: true,
          parser: :string
        outfile: [
          value_name: "OUTPUT_FILE",
          help: "File to write statistics to",
          required: false,
          parser: :string
      flags: [
        print_header: [
          short: "-h",
          long: "--print-header",
          help: "Specifies wheather to print header before the outputs",
          multiple: false,
        verbosity: [
          short: "-v",
          help: "Verbosity level",
          multiple: true,
      options: [
        date_from: [
          value_name: "DATE_FROM",
          short: "-f",
          long: "--from",
          help: "Start date for the period",
          parser: fn(s) ->
            case Date.from_iso8601(s) do
              {:error, _} -> {:error, "invalid date"}
              {:ok, _} = ok -> ok
          required: true
        date_to: [
          value_name: "DATE_TO",
          short: "-t",
          long: "--to",
          help: "End date for the period",
          parser: fn(s) ->
            case Date.from_iso8601(s) do
              {:error, _} -> {:error, "invalid date"}
              {:ok, _} = ok -> ok
          required: false,
          default: &Date.utc_today/0
      subcommands: [
        validate: [
          name: "validate",
          about: "Validates the raw contents of a file",
          args: [
            file: [
              value_name: "FILE",
              help: "File with raw data to validate",
              required: true,
              parser: :string
    ) |> Optimus.parse!(argv) |> IO.inspect

(The whole sample code can be found in optimus_example repo.)

Nearly all of the configuration options above are not mandatory.

Also most configuration parameters are self-explanatory, except parser. For options and positional arguments parser is a lambda which accepts a string argument and returns either {:ok, parsed_value} or {:error, string_reason}. There are also some predefined parsers which are denoted by atoms: :string, :integer and :float. No parser means that :string parser will be used.

Not required options can have a default value. Both a term (string, number, etc.) or a lambda with zero arity can be used. If the option accepts multiple values, the default value should be a list, for example [1.0] or fn -> ["x", "y"] end.

Now if we try to launch our compiled escript without any args we'll see the following:

The following errors occured:
- missing required arguments: INPUT_FILE
- missing required options: --from(-f), --to(-t)

    statcalc --help

to see available options

There are several things to note:

  • the script exited (in Optimus.parse!) since we haven't received a valid set of arguments;
  • a list of errors is displayed (and it's as full as possible);
  • a user is offered to launch statcalc with --help flag which is automatically handled by Optimus.

If we launch statcalc --help, we'll see the following:

>./statcalc --help
Statistic metrics calculator 1.2.3
John Smith [email protected]
Utility for calculating statistic metrics of values read from a file for a certain period of time

    statcalc [--print-header] --from DATE_FROM --to DATE_TO INPUT_FILE [OUTPUT_FILE]
    statcalc --version
    statcalc --help
    statcalc help subcommand


    INPUT_FILE         File with raw data
    OUTPUT_FILE        File to write statistics to


    -h, --print-header        Specifies wheather to print header before the


    -f, --from        Start date for the period
    -t, --to          End date for the period  (default: 2017-12-20)


    validate        Validates the raw contents of a file

The things to note are:

  • Optimus formed a formatted help information and also exited;
  • it also offers some other autogenerated commands (--version and help subcommand).

Now if we finally produce a valid list of args, we'll have our arguments parsed:

>./statcalc --print-header -f 2016-01-01 -t 2016-02-01 infile.raw outfile.dat
  args: %{
    infile: "infile.raw",
    outfile: "outfile.dat"
  flags: %{
    print_header: true
  options: %{
    date_from: ~D[2016-01-01],
    date_to: ~D[2016-02-01]
  unknown: []

Optimus.ParseResult is a struct with four fields: args, flags, options, which are maps, and unknown, which is a list. Things to note are:

  • unknown list is always empty if we set allow_unknown_args: false for our (sub)command;
  • values in args, flags and options maps are kept under keys specified in configuration;
  • for options with multiple: true the value is a list;
  • for flags without multiple: true the value is a boolean;
  • for flags with multiple: true the value is an integer (representing the number of occurrences of a flag).

One can load configuration from a YAML file:

optimus = Optimus.from_yaml!("path/to/config.yaml")

But in this case custom parsers are obviously unavailable.


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