@metalsmith/permalinks

A Metalsmith plugin that applies a custom permalink pattern to files, and renames them so that they're nested properly for static sites (converting about.html into about/index.html).

Installation

NPM:

npm install @metalsmith/permalinks

Yarn:

yarn add @metalsmith/permalinks

Usage

import { dirname } from 'path'
import { fileURLToPath } from 'url'
import Metalsmith from 'metalsmith'
import permalinks from '@metalsmith/permalinks'

const __dirname = dirname(fileURLToPath(import.meta.url))

Metalsmith(__dirname).use(
  permalinks({
    pattern: ':title'
  })
)

The pattern can contain a reference to any piece of metadata associated with the file by using the :PROPERTY syntax for placeholders.

If no pattern is provided, the files won't be remapped, but the permalink metadata key will still be set, so that you can use it for outputting links to files in the template.

The pattern can also be set as such:

metalsmith.use(
  permalinks({
    // original options would act as the keys of a `default` linkset,
    pattern: ':title',
    date: 'YYYY',

    // each linkset defines a match, and any other desired option
    linksets: [
      {
        match: { collection: 'blogposts' },
        pattern: 'blog/:date/:title',
        date: 'mmddyy'
      },
      {
        match: { collection: 'pages' },
        pattern: 'pages/:title'
      }
    ]
  })
)

Optional permalink pattern parts

The pattern option can also contain optional placeholders with the syntax :PROPERTY?. If the property is not defined in a file's metadata, it will be replaced with an empty string ''. For example the pattern :category?/:title applied to a source directory with 2 files:

--- title: With category category: category1 ---

--- title: No category ---

would generate the file tree:

build
├── category1/with-category/index.html
└── no-category/index.html

Dates

By default any date will be converted to a YYYY/MM/DD format when using in a permalink pattern, but you can change the conversion by passing a date option:

metalsmith.use(
  permalinks({
    pattern: ':date/:title',
    date: 'YYYY'
  })
)

It uses moment.js to format the string.

Slug options

You can finetune how a pattern is processed by providing custom slug options. By default slugify is used and patterns will be lowercased.

You can pass custom slug options:

metalsmith.use(
  permalinks({
    slug: {
      replacement: '_',
      lower: false
    }
  })
)

The following makes everything snake-case but allows ' to be converted to -

metalsmith.use(
  permalinks({
    slug: {
      remove: /[^a-z0-9- ]+/gi,
      lower: true,
      extend: {
        "'": '-'
      }
    }
  })
)

Handling special characters

If your pattern parts contain special characters like : or =, specifying slug.strict as true is a quick way to remove them:

metalsmith.use(
  permalinks({
    slug: {
      lower: true,
      strict: true
    }
  })
)

Custom 'slug' function

If the result is not to your liking, you can replace the slug function altogether. For now only the js version of syntax is supported and tested.

metalsmith.use(
  permalinks({
    pattern: ':title',
    slug: require('transliteration').slugify
  })
)

There are plenty of other options on npm for transliteration and slugs. https://www.npmjs.com/browse/keyword/transliteration.

Relative Files

When this plugin rewrites your files to be permalinked properly, it will also duplicate sibling files so that relative links like css/style.css will be preserved nicely. You can turn this feature off by setting the relative option to false.

For example for this source directory:

src/
  css/
    style.css
  post.html

Here's what the build directory would look like with relative on:

build/
  post/
    index.html
    css/
      style.css
  css/
    style.css

And here's with relative off:

build/
  post/
    index.html
  css/
    style.css

relative can also be set to folder, which uses a strategy that considers files in folder as siblings if the folder is named after the html file.

For example using the folder strategy with this source directory:

src/
  post.html
  post/
    image.jpg

Here's what the build directory would look like with relative set to folder:

build/
    index.html
    image.jpg

Skipping Permalinks for a file

A file can be ignored by the permalinks plugin if you pass the permalink: false option to the yaml metadata of a file. This is useful for hosting a static site on AWS S3, where there is a top level error.html file and not an error/index.html file.

For example, in your error.md file:

---
template: error.html
title: error
permalink: false
---

Overriding the permalink for a file

Using the permalink property in a file's front-matter, its permalink can be overridden. This can be useful for transferring projects over to Metalsmith where pages don't follow a strict permalink system.

For example, in one of your pages:

---
title: My Post
permalink: "posts/my-post"
---

Overriding the default index.html file

Use indexFile to define a custom index file.

metalsmith.use(
  permalinks({
    indexFile: 'alt.html'
  })
)

Ensure files have unique URIs

Normally you should take care to make sure your source files do not permalink to the same target.
When URI clashes occur nevertheless, the build will halt with an error stating the target file conflict.

metalsmith.use(
  permalinks({
    duplicates: 'error'
  })
)

There are 3 other possible values for the duplicates option: index will add an -<index> suffix to other files with the same target URI, , overwrite will silently overwrite previous files with the same target URI.

The third possibility is to provide your own function to handle duplicates, with the signature:

function paginateDupes(targetPath, files, filename, options) => {
  let target,
    counter = 0,
    postfix = ''
  while (files[target]) {
    postfix = `/${++counter}`
    target = path.join(`${targetPath}${postfix}`, options.indexFile)
  }
  return target
}

Return an error in the custom duplicates handler to halt the build.
The example above is a variant of the index value, where 2 files targeting the URI gallery will be written to gallery/1/index.html and gallery/2/index.html.

Note: The duplicates option combines the unique and duplicatesFail options of version < 2.4.1. Specifically, duplicatesFail:true maps to duplicates:'error', unique:true maps to duplicates:'index', and unique:false or duplicatesFail:false map to duplicates:'overwrite'.

Debug

To enable debug logs, set the DEBUG environment variable to @metalsmith/permalinks:

metalsmith.env('DEBUG', '@metalsmith/permalinks*')

Alternatively you can set DEBUG to @metalsmith/* to debug all Metalsmith core plugins.

CLI usage

To use this plugin with the Metalsmith CLI, add @metalsmith/permalinks to the plugins key in your metalsmith.json file:

{
  "plugins": [
    {
      "permalinks": {
        "pattern": ":title"
      }
    }
  ]
}

License

MIT