Parse argument aliases in Deno

You can parse command-line arguments in Deno with the standard flags module:

import { parse } from "https://deno.land/std/flags/mod.ts";

console.dir(parse(Deno.args));
deno run https://deno.land/std/examples/flags.ts -a beep -b boop

{ _: [], a: 'beep', b: 'boop' }

The parse function has a second options argument where you can assign aliases. Before we do that, let’s use a more description example.

Example scenario

Say you have a script, log.ts, that takes a message to display in the terminal. We would use our script like this:

deno run log.ts --message "Hello world"

Hello world

Now let’s alias the --message flag to -M for ease of use.

Alias option

When we call parse in our script on Deno.args, we want to provide an additional options object with a key aliases.

That will be assigned to another object that will map flags to their aliases:

// log.ts
import { parse } from "https://deno.land/std/flags/mod.ts";

const flagToAliasMap = {
message: 'M'
}

const parsedArgs = parse(Deno.args, { aliases: flagToAliasMap })

console.log(parsedArgs.message)

Now we can call our script with those aliases:

deno run log.ts -M "That's better"

That's better

With that, the flags module does all of the hard lifting for you!

Wrap up

Two things to note about aliases:

  1. flags doesn’t care whether you use one or two hyphens for aliases, so -M and --M will both work.
  2. Aliases are case sensitive, so you’ll have to map m and M separately.

Happy coding!

About

Sean McPherson

My name is Sean McPherson (SeanMcP), and I am a software engineer and educator in Pittsburgh, PA. I have given conference talks, lead workshops, and organized meetups. Here I write articles about programming for developers of all levels.