Use highlight.js from command line on HTML file.
npm install highlight.js-cli -g
Input it taken from stdin and output to stdout if not specified otherwise (see example below). The default selector is "pre code", i.e. <pre><code>...</code></pre>. Other DOM elements than those fitting the selector are not highlighted.
To highlight a file:
hljs < input.html > output.html
You can also use the --o parameter:
hljs --o output.html < input.html
To highlight a multi-line string from stdin:
hljs <<EOF
<pre><code>
var stuff="asd"
</code></pre>
EOF
To use a different selector use --s option. You can use any valid jQuery selector, for example:
hljs --s=".highlight" < input.html > output.html
Highlight.js-cli will try to pick up the language from the class, if specified:
<pre><code class="haskell">
main :: IO ()
</code></pre>