Syntax & Conventions

Basics

leaf command: leaf commands are the commands at the last of the CLI that takes arguments, options and flags, e.g the show command below

node command: node commands are the commands at the middle or first of the CLI that contains sub-commands, e.g the remote command below

git remote show origin

arguments: arguments are command line arguments that required at the leaf command

flags: flags are command line options that has no arguments, e.g --flag or -f (short flag).

options: options are command line options that has arguments, e.g --name Sam or -n Sam, also --name=Sam or -nSam.

When used on function expressions, @cast and @main have the same convention on how they convert your expressions to commands, these are

  • function arguments are parsed as command arguments:
    • value will be converted automatically if arguments has type annotation
    • optional arguments are allowed
  • function keyword arguments are parsed as command flags or options:
    • keyword arguments must have default value
    • keyword arguments of type Bool can only have false as default value, which will be treated as flags that allow short flags.
    • value will be converted automatically if keyword arguments has type annotation
  • function doc string can use section names: Arguments, Options and Flags to annotate your CLI:
    • short options or short flags can be declared via -f, flag or -o, --option <name> (see example below)
Note

to be compatible with shell options, variable names with underscore _ will be automatically replaced with dash -. As a result, the corresponding doc string should use dash - instead of _ as well, e.g kwargs name dash_dash will be converted to --dash-dash option/flag in terminal, and its corresponding doc string should be - `--dash-dash`: <arg>.

Help and Version

There are two flags are always generated and always have highest priority, they are -h,--help and --version. The version is automatically read from the corresponding project's Project.toml if it's not found then it's set to 0.0.0.

Doc String Syntax

the docstring of each @cast or @main annotated object have a few special section. The function or module signature is ignored for generating CLI help page,

Description

The description of the command is seperated as brief and detailed description. The special sections are organized as following:

  • The brief description is the first paragraph of the docstring.
  • The long detailed description can be specified using #Intro or #Introduction section.

for example

"""
    command(args1, args2, args3, args4)

the brief description of the command.

# Intro

the long description of the command,
asdmwds dasklsam xasdklqm dasdm, qwdjiolkasjdsa
dasklmdas weqwlkjmdas kljnsadlksad qwlkdnasd
dasklmdlqwoi, dasdasklmd qw,asd. dasdjklnmldqw.
"""

Arguments

The argument description can be specified using #Args or #Arguments section. The syntax must be

- `<arg name>`: <description of the argument>

for example

"""
    command(args1, args2, args3, args4)

the brief description of the command.

# Intro

the long description of the command,
asdmwds dasklsam xasdklqm dasdm, qwdjiolkasjdsa
dasklmdas weqwlkjmdas kljnsadlksad qwlkdnasd
dasklmdlqwoi, dasdasklmd qw,asd. dasdjklnmldqw.

# Args

- `arg1`: argument 1.
- `arg2`: argument 2.
- `arg3`: argument 3.
- `arg4`: argument 4.
"""

Options

the options can be specified in #Options section, the option must have a prefix --, and optionally have -<first letter> to specify its short option. All underscore _ in the option name will be converted to a dash - for option names, for example.

The value string after = (e.g -s=<value>) can give user specified hint or the default hint will be the default value's Julia expression.

# Options

- `--short, -s`: short option using default hint.
- `--short-space, -s <value>`: short option using given hint.
- `--short-assign, -s=<value>`: short option using given hint.
- `--long`: long option using default hint.
- `--long-space <value>`: long option using given hint.
- `--long-assign=<value>`: long option using given hint.
- `--short_underscore, -s <value>`: short option with underscore.

Flags

the flags can be specified using #Flags section, the rest are similar to #Options except there are no value hints.

Special Arugment/Options Types

there are a few special argument/option types defined to generate special shell completions.

Modules = [Comonicon.Arg]

Working with option types from Configurations

If the option type is defined using @option then Comonicon can provide the following syntax to read a configuration file.

using Test
using Comonicon
using Configurations

@option struct OptionA
    a::Int
    b::Int
end

@option struct OptionB
    option::OptionA
    c::Int
end

"""
# Options

- `-c, --config <path/to/option/or/specific field>`: config.
"""
@main function run(;config::OptionB)
    @test config == OptionB(OptionA(1, 1), 1)
end

can be used with the following syntax

command --config.c=1 --config.option.a=1 --config.option.b=1
command --config=config.toml
command -c config.toml
command -c config.toml --config.option.b=2 # change a field of config.toml

Dash Seperator

Dash seperator -- is useful when the CLI program contains scripts that accepts command line inputs, e.g a custom command run that execute Julia script

run --flag -- script.jl a b c

one will need to seperate the input of run and script.jl for disambiguity sometimes,then the dash seperator comes useful for this case.

Plugins

Most complicated CLIs support plugins, this is acheived by checking if there is a command line executable with the following name pattern

<main command name>-<plugin name>

for example, git have plugin program called git-shell and can be called as git shell, this is by default turned off, but one can enable this feature by setting the following in (Julia)Comonicon.toml

[command]
plugin=true