`std.cli`

Declarative argument parsing. Describe the interface, get a parser and a help screen.

import std.cli
import std.os

spec = {
    program: "report",
    options: [
        { name: "format", short: "f", default: "text", help: "output format" },
        { name: "verbose", flag: true, help: "explain what is happening" },
    ],
    args: [
        { name: "input", help: "the file to read" },
    ],
}

opts = cli.parse(spec, os.args())

print(opts.format)      # "text" unless --format was given
print(opts.verbose)     # false unless --verbose
print(opts.input)
print(opts.rest)        # anything after the declared positionals

The surface

call
`cli.parse(spec, argv)`	parse, or error with a usage message
`cli.help(spec)`	the generated help text

The spec

program - the name shown in usage.
options - each { name, short?, default?, flag?, help? }. A flag takes no

value and defaults to false.

args - positional parameters, in order.
rest - whatever is left over, always present in the result.

Why declarative

The parser and the help text come from one description, so they cannot disagree. Hand-rolled argument parsing drifts from its --help output almost immediately, and the drift is invisible until someone follows the help and gets an error.

With `std.defaults`

A natural pairing: put the defaults in ecko.json and let flags override them.

import std.defaults
opts = cli.parse(spec, os.args())
port = if opts.port == null { defaults.port } else { int(opts.port) }

The manifest holds what the project wants; the command line holds what this run wants. See std.defaults.

The `cli` package

There is also a Layer-3 cli package written in Ecko, with typed flags and richer usage generation. This module is the built-in, no-dependency option; the package goes further.

std.cli