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A Commander for C3 CLI applications

Serp is a library for creating powerful modern CLI applications in C3. Inspired by cobra.

Overview

Serp provides:

• Easy subcommand-based CLIs: app serve, app fetch, etc.
• Fully POSIX-compliant flags (including short and long versions)
• Nested subcommands
• Automatic help generation for commands and flags

In the works:

• Automatic help flag recognition of -h, --help (TODO)
• Command aliases so you can change things without breaking them

Concepts

Serp is built on a structure of commands and flags - heavely inspired by cobra.

Commands represent actions and flags are modifiers for those actions.

Well-designed CLI apps follow a certain usage pattern; the commands should read like sentences: app verb noun or app command argument --flags.

Commands

Command is the central point of the application. A command can have children commands an optionally run an action.

Create a command with command::new:

import serp::command;

Command *root = command::new(
    use: "app",
    run: fn void!(Command *c, String[] args, Option[] opts) {
        io::printn("hello app");
    }
);

To add subcommands, use the Command.add_command(Command*) function:

root.add_command(
    command::new(
        use: "init",
        run: fn void!(Command *c, String[] args, Option[] opts) {
            io::printn("app init");
        }
    )
);

Flags

A flag is a way to modify the behavior of a command. POSIX-compliant flags are supported.

Flags can be defined per command with Command.add_flag(Flag):

root.add_flag({.shortopt = 'p', .longopt = 'path', .optarg = true});

The above example will set a flag on the root command that expects an optional argument. The flag can then be set with -p or --path on the command line.

The parameter to the add_flag function is a struct Flag that contains the following fields:

struct Flag {
        char    shortopt; // short option name, e.g. 'p'
        String  longopt;  // long option name, e.g. "path"
        bool    optarg;   // set true if flag has an optional argument
        String  desc;     // describe the purpose of the flag
}

Example

module serp_app;

import serp;

import std::io;

fn void? root_cmd(Command *c, String[] args, Option[] opts)
	=> show_args_and_opts("root", c, args, opts);

fn void? init_cmd(Command *c, String[] args, Option[] opts)
	=> show_args_and_opts("init", c, args, opts);

fn void? add_cmd(Command *c, String[] args, Option[] opts)
	=> show_args_and_opts("add", c, args, opts);


fn void? show_args_and_opts(String cmd, Command *c, String[] args, Option[] opts)
{
	io::printfn("Command: %s", cmd);
	io::printn("--------");
	io::printfn("Positional arguments:\n\t%s", args);
	if (opts.len)
	{
		io::printfn("\nParsed flags:");
		foreach (opt : opts) io::printf("\t%s", opt);
	}
	io::printf("\nUsage message:\n");
	io::printf("--------------");
	return c.usage();
}

fn void main(String[] args) => @assert_leak()
{
	Command *root = command::new(use: "app [commands] [flags]", run: &root_cmd)
	.describe("describe your command here")
	.add_command(
		command::new(use: "init [flags]", run: &init_cmd)
		.add_flag({.shortopt = 'p', .desc = "path", .optarg = true})
		.add_flag({.shortopt = 'n', .desc = "name", .optarg = true})
		.describe("'init' your app with this command")
	)
	.add_command(
		command::new(use: "add [flags] <name>", run: &add_cmd)
		.add_flag({.shortopt = 'f', .longopt = "force"})
		.describe("'add' something to your app")
	);

	defer root.free();

	root.execute(args)!!;
}

See source.

Install

Add the path to the serp.c3l folder to dependency-search-paths and serp to dependencies in your project.json file:

{
    "dependency-search-paths": ["lib", "<path_to_serp.c3l_folder>"],
    "dependencies": ["serp"]
}