clip - A CLI Option Parser for Gleam

clip is a library for parsing command line interface options.

Simple Example

import argv
import clip
import clip/opt
import gleam/io
import gleam/string

type Person {
  Person(name: String, age: Int)
}

fn command() {
  clip.command({
    use name <- clip.parameter
    use age <- clip.parameter

    Person(name, age)
  })
  |> clip.opt(opt.new("name") |> opt.help("Your name"))
  |> clip.opt(opt.new("age") |> opt.int |> opt.help("Your age"))
}

pub fn main() {
  let result =
    command()
    |> clip.add_help("person", "Create a person")
    |> clip.run(argv.load().arguments)

  case result {
    Error(e) -> io.println_error(e)
    Ok(person) -> person |> string.inspect |> io.println
  }
}

$ gleam run -- --help
   Compiled in 0.00s
    Running cli.main
person -- Create a person

Usage:

  person [OPTIONS]

Options:

  (--name NAME) Your name
  (--age AGE)   Your age
  [--help,-h]   Print this help

$ gleam run -- --name Drew --age 42
   Compiled in 0.00s
    Running cli.main
Person("Drew", 42)

Using clip

clip is an “applicative style” options parser. To use clip, follow these steps:

1. First, invoke clip.command providing a function to be called with your parsed options. This function can be built using the parameter syntax. Alternatively, you can directly provide a curried function, meaning a two argument function looks like fn(a) { fn(b) { do_stuff(a, b) } }.
2. Next, use the |> operator along with clip.opt, clip.flag, and clip.arg to parse command line arguments and provide them as parameters to the function given to clip.command.
3. Optionally use clip.add_help to generate help text for your command. The user can view this help text via the --help,-h flag.
4. Finally, run your parser with clip.run, giving it the command you have built and the list arguments to parse. I recommend using the argv library to access these arguments from both erlang and javascript.

Types of Options

clip provides three types of options:

1. An Option is a named option with a value, like --name "Drew". You create Options with the clip/opt module and add them to your command with the clip.opt function.
2. A Flag is a named option without a value, like --verbose. If provided, it produces True, if not provided it produces False. You create Flags with the clip/flag module and add them to your command with the clip.flag function.
3. An Argument is a positional value passed to your command. You create Arguments with the clip/arg module and add them to your command with the clip.arg, clip.arg_many, and clip.arg_many1 functions.

Take a look at the examples for more information.