7.9 Use a custom HTML template (*)

We mentioned LaTeX templates in Section 6.10. You can also specify a custom HTML template for Pandoc to convert Markdown to HTML. Below is a brief example template:

<html>
  <head>
    <title>$title$</title>
    $for(css)$
    <link rel="stylesheet" href="$css$" type="text/css" />
    $endfor$
  </head>
  <body>
  $body$
  </body>
</html>

You can see that the template contains a few variables such as $title$ and $body$. You can find the full list of Pandoc variables and their meanings at https://pandoc.org/MANUAL.html#templates.

The template gives you the ultimate power to customize the HTML output. For example, you can include arbitrary CSS stylesheets or JavaScript code or libraries in the <head> area. For example, we could use a Boolean variable draft to indicate whether the document is a draft or a final version:

<head>
<style type="text/css">
.logo {
  float: right;
}
</style>
</head>

<body>
<div class="logo">
$if(draft)$
<!-- use draft.png to show that this is a draft -->
<img src="images/draft.png" alt="Draft mode" />
$else$
<!-- insert the formal logo if this is final -->
<img src="images/logo.png" alt="Final version" />
$endif$
</div>

$body$
</body>

Then we can set the variable draft to true or false in the YAML metadata of the Rmd document, e.g.,

---
title: "An Important Report"
draft: true
---

To apply a template to an Rmd document, you can save the template to a file, and pass the file path to the template option of html_document, e.g.,

output:
  html_output:
    template: my-template.html

The rmarkdown package uses a custom HTML template shipped with the package, which is different from Pandoc’s default template. To use the latter, you can specify template: null.