Hugo provides the ability for you to highlight source code in _two different ways_— either pre-processed server side from your content, or to defer the processing to the client side, using a JavaScript library.
**The advantage of client side** is that it doesn’t cost anything when building your site and some of the highlighting scripts available cover more languages than Pygments does.
For the pre-processed approach, highlighting is performed by an external Python-based program called [Pygments](http://pygments.org/) and is triggered via an embedded Hugo shortcode (see example below). If Pygments is absent from the path, it will silently simply pass the content along unhighlighted.
+ Install Python from [python.org](https://www.python.org/downloads/). Version 2.7.x is already sufficient.
+ Run `pip install Pygments` in order to install Pygments. Once installed, Pygments gives you a command `pygmentize`. Make sure it sits in your PATH, otherwise Hugo cannot find it.
Hugo gives you two options that you can set with the variable `pygmentsuseclasses` (default `false`) in `config.toml` (or `config.yaml`).
1. Color-codes for highlighting keywords are directly inserted if `pygmentsuseclasses = false` (default). See in the example below. The color-codes depend on your choice of the `pygmentsstyle` (default `"monokai"`). You can explore the different color styles on [pygments.org](http://pygments.org/) after inserting some example code.
2. If you choose `pygmentsuseclasses = true`, Hugo includes class names in your code instead of color-codes. For class-names to be meaningful, you need to include a `.css`-file in your website representing your color-scheme. You can either generate this `.css`-files according to this [description](http://pygments.org/docs/cmdline/) or download the standard ones from the [GitHub pygments-css repository](https://github.com/richleland/pygments-css).
Highlighting is carried out via the in-built shortcode `highlight`. `highlight` takes exactly one required parameter of language, and requires a closing shortcode. Note that `highlight` is _not_ used for client-side javascript highlighting.
Options to control highlighting can be added as a quoted, comma separated key-value list as the second argument in the shortcode. The example below will highlight as language `go` with inline line numbers, with line number 2 and 3 highlighted.
```
{{</* highlight go "linenos=inline,hl_lines=2 3" */>}}
var a string
var b string
var c string
var d string
{{</* / highlight */>}}
```
Supported keywords: `style`, `encoding`, `noclasses`, `hl_lines`, `linenos`. Note that `style` and `noclasses` will override the similar setting in the global config.
The keywords are the same you would using with Pygments from the command line, see the [Pygments doc](http://pygments.org/docs/) for more info.
This example uses the popular [Highlight.js] library, hosted by [Yandex], a popular Russian search engine.
In your `./layouts/partials/` (or `./layouts/chrome/`) folder, depending on your specific theme, there will be a snippet that will be included in every generated HTML page, such as `header.html` or `header.includes.html`. Simply add the css and js to initialize [Highlight.js]:
Prism is another popular highlighter library, used on some major sites. Similar to Highlight.js, you simply load `prism.css` in your `<head>` via whatever Hugo partial template is creating that part of your pages, like so:
To use client-side highlighting, most of these javascript libraries expect your code to be wrapped in semantically correct `<code>` tags, with the language expressed in a class attribute on the `<code>` tag, such as `class="language-abc"`, where the `abc` is the code the highlighter script uses to represent that language.
The script would be looking for classes like `language-go`, `language-html`, or `language-css`. If you look at the page's source, it would be marked up like so:
The markup in your content pages (e.g. `my-css-tutorial.md`) needs to look like the following, with the name of the language to be highlighted entered directly after the first "fence", in a fenced code block:
