arg_parse: command line parser for Erlang

A mini-framework to create complex cli. Inspired by Python argparse.

Follows conventions of Unix Utility Argument Syntax.

    argparse [-abcDxyz][-p arg][operand]

Argument parser

Converts list of strings (command line) into an argument map,and a command path; see argparse reference for detailed description.

cli mini-framework

Make a step beyond parser, and export existing Erlang functions: cli reference

Basic example

cli is naturally suitable for building small escript-based apps:

    #!/usr/bin/env escript

    -export([main/1, cli/0, rm/1]).
    -behaviour(cli).
    -mode(compile). %% evaluated module cannot contain callbacks

    main(Args) ->
        cli:run(Args, #{progname => "simple"}).

    cli() ->
      #{
        handler => {?MODULE, rm},
        arguments => [
          #{name => force, short => $f, type => boolean, default => false},
          #{name => recursive, short => $r, type => boolean, default => false},
          #{name => dir}
      ]}.

    rm(#{force := Force, recursive := Recursive, dir := Dir}) ->
        io:format("Removing ~s (force ~s, recursive: ~s)~n",
            [Dir, Force, Recursive]).

The example above does not have sub-commands, and implements rm/1 handler, that serves as an entry point with parsed arguments. Help options are added automatically:

    $ ./erm --help
    usage: erm [-fr] <dir>

    Optional arguments:
      dir
      -r  recursive, [false]
      -f  force, [false]

Calc: cli with multiple commands

Calculator implements several commands, with sub-commands available. Full source code here: doc/examples/escript/calc

Command definitions:

    cli() ->
        #{
            commands => #{
                "sum" => #{
                    arguments => [
                        #{name => num, nargs => nonempty_list, type => int, help => "Numbers to sum"}
                    ]
                },
                "math" => #{
                    commands => #{
                        "sin" => #{handler => {math, sin, undefined}},
                        "cos" => #{},
                        "tan" => #{handler => {math, tan, undefined}}
                    },
                    arguments => [
                        #{name => in, type => float, help => "Input value"}
                    ]
                },
                "mul" => #{
                    arguments => [
                        #{name => left, type => int},
                        #{name => right, type => int}
                    ]
                }
            }
        }.

The calculator provides "sum" command that prints a sum of integer numbers:

    $ ./calc sum 1 2 3
    6

Math sub-commands provide trigonometric functions:

    $ ./calc math cos 1.4
    0.16996714290024104
    $ ./calc math sin 1.4
    0.9854497299884601

Complex applications

cli is capable of handling releases containing hundreds of modules implementing cli behaviour. Commands may be exported from multiple modules and applications. cli makes best efforts to merge commands exported, format usage output and error messages.

See example: doc/examples/multi

This example contains two modules, multi_math.erl and multi_string.erl.

Use rebar3 escriptize to build the application. Try various commands, e.g. ./multi math cos 1.0, or ./multi string lexemes 1+2+3+4 -s + to get a feeling!

Argument parser alone

It is possible to use argument parser alone, without the cli mini-framework:

    #!/usr/bin/env escript

    main(Args) ->
        #{force := Force, recursive := Recursive, dir := Dir} =
            arg_parse:parse(Args, cli()),
        io:format("Removing ~s (force: ~s, recursive: ~s)~n",
            [Dir, Force, Recursive]).

    cli() ->
        #{arguments => [
            #{name => force, short => $f, type => boolean, default => false},
            #{name => recursive, short => $r, type => boolean, default => false},
            #{name => dir}
        ]}.

Help and usage information

cli automatically prints usage, if command line parser reports an error. An attempt is made to guess the most relevant command. Argument help can be customised.

Build

This project requires OTP-22 or above. Simple integration is available via Hex and rebar3.

    {deps, [argparse]}.

Known incompatibilities

In comparison with Python implementation, argparse for Erlang:

• boolean flag (option) automatically uses {store, true}
• all positional arguments are required by default (even when nargs is 'maybe')
• first-class (sub) commands, slightly differently from argparse
• implicit --help/-h is not a part of argparse (but implemented in cli)

Commands vs. positional arguments: command always takes precedence over a positional argument. Commands form exclusive groups, e.g. only one command can be followed at a time.

Supported command line syntax

• command (priority positional argument) : ectl {crawler|reader|writer}
• command, and sub-command: ectl crawler {start|stop|check}
• positional argument (required): ectl
• positional argument (with default): ectl []
• boolean flag: ectl [-rf]
• required flag: ectl -r
• short optional argument: ectl [-i ]
• short optional: ectl [-i []]
• required short option: ectl -i
• long option flag: ectl [--foo]
• long optional argument: ectl [--foo ]
• required long: ectl --foo
• long, arg=value form: ectl --foo=arg
• list of arguments: ectl , ...

Expected features

To be considered after 1.2.0:

• search for commands and arguments (mini-man)
• abbreviated long forms
• mutual exclusion groups
• shell auto-complete
• automatically generated negative boolean long forms "--no-XXXX"