With hygen, every time you spot a repetitive task, or a hidden structure in files you're editing, you'll quickly make a new generator.

$ hygen generator new --name mailer
                              `-------- just a name you pick.

Loaded templates: _templates
       added: _templates/mailer/new/hello.ejs.t
                                       `------ your template file.

$ hygen

Error: please specify a generator.

Available actions:
generator: new, with-prompt
mailer: new
     `----------- your new generator is already here!

The moment we add a generator under _templates, it's ready to use. Here's hello.ejs.t that was placed in the template folder for you:

to: app/hello.js
const hello = `
This is your first hygen template.

Learn what it can do here:


To make real mailer, let's copy this file and rename it a bit:

$ mv _templates/mailer/new/{hello.js,html.ejs.t}
$ cp _templates/mailer/new/{html.ejs.t,text.ejs.t}

We use a .t suffix because it disables our editor trying to be smart - use what ever you like. For this example these files represent the HTML and text forms of an email sender.

Creative Freedom

hygen doesn't care about file names or file types in your generator folders. It only cares about folder structure and the contents of your files.

Also note that each template has a frontmatter delimited by a pair of ---'s. In our example, we have a special to: property which tells hygen where to put the generated file. We'll see more of these in templates.


Let's look at our folder structure:


Every time you call it, hygen mailer new automagically picks up the closest _templates folder, and renders all files in mailer/new. In this case it's html.ejs.t and text.ejs.t.

As of PR 102 Hygen will recursively walk your template folder, so that you can structure your generators as elaborately as you wish.

Hygen is Contextual

hygen simplifies things by asserting "command structure is folder structure".

hygen will pick up the _templates in your current working directory.

CLI Arguments

To give hygen arguments via CLI, we follow this pattern:

$ hygen mailer new --name foobar --message hello --version 1

Any double-dash (--) argument becomes a variable we can use later in our templates. In the example above we can use name, message and version.

Here's the contents of the template html.ejs.t with the variables in place:

to: app/emails/<%= name %>.html
<h1>Hello <%= name %></h1>
<%= message %>
(version <%= version %>)

Try making the text variant yourself by editing text.ejs.t. Note: you want to put it in the correct place with to:.

Interactive Prompt

To create an interactive generator, add prompt.js file to the generator root directory.

    new/           <-- the mailer new generator
      prompt.js    <-- your prompt file!

For example, to ask for the message input variable, add to prompt.js:

module.exports = [
    type: 'input',
    name: 'message',
    message: "What's your message?"

The format is based on enquirer. Let's use the message variable now:

to: app/emails/<%= name %>.txt
<%= message %>

Note that the name variable has to come from the CLI. To generate, we'll do this:

$ hygen mailer new --name fancy-mailer

Which will ask the user for the message, and generate all contents.

Advanced Interactive Prompt

It's possible to create a a multi-step prompt where you ask some questions, run some computation and ask some more questions.

In addition, it's possible to skip prompting, or re-shape parameters that were given to you from either CLI or prompt, so that you can do it in a central place.

You can "enable" advanced params and prompting by replacing your prompt.js file with an index.js file in your action:


Here's how you can use index.js to build a two-step prompting flow. Instead of exporting an array of question types as with the prompt.js file, you now need to export an object with a function called prompt:

// my-generator/my-action/index.js
module.exports = {
  prompt: ({ prompter, args }) =>
        type: 'input',
        name: 'email',
        message: "What's your email?"
      .then(({ email }) =>
          type: 'input',
          name: 'emailConfirmation',
          message: `Please type your email [${email}] again:`

The prompt function gets a data structure with an prompter field you can use.

For completeness, here is a a more elaborate use of prompts (thanks @jaykoontz).

You can skip prompting conditionally using custom logic:

// my-generator/my-action/index.js
module.exports = {
  prompt: ({ prompter, args }) => {
    if (args.age > 18) {
      return Promise.resolve({ allow: true })
    return prompter.prompt({
      type: 'input',
      name: 'age',
      message: 'whats your age?'

You can skip physically prompting and use params to build more sophisticated parameters out of your CLI parameters:

// my-generator/my-action/index.js
module.exports = {
  params: ({ args }) => {
    return { moreConvenientName: args.foobamboozle }
Params and Prompts are The Same

If you think about it, prompting for variables or reshaping CLI arguments lead to the same goal: new parameters. But to make a future-proof API, we've separated the two intents to the prompt and params functions.

Documenting Your Generators

Since there's a special message prop you can use in any template, you can use that to build generator help screens. Ultimately, your generator should be documenting itself.

Looking at our generator layout from before, we add a help action:


Our index.ejs.t is simply a blank template, with just a message: prop:

message: |
  - hygen {bold mailer} new --name [NAME]

The special | annotation is a YAML literal block. Should you need it, here's a quick YAML refresher.

Note that in message you can have a special coloring syntax, which can spice up your self-documenting generators.

Here's a few examples:

{bold mailer}
{red mailer}
{underline mailer}
{green mailer}

For more styles check out chalk.

Selecting Parts of a Generator

In addition to what we've seen until now, hygen lets the user select parts of a generator.

The complete form is:


Where SUBACTION is a regular expression or a simple string hygen uses to pick up the subset of templates you want from a generator.

Using our mailer example, this generates only the text part:

$ hygen mailer new:text --name textual-mailer

Because we have a file named text.ejs.t, the string text in new:text will match it.

In the same way we could have used a proper regular expression:

$ hygen mailer new:.*xt --name textual-mailer

That's about it for generators.

That's it for now, you're invited to take a look at the FAQ, and Packages.