Compile a referenced LESS file into CSS with PHP automatically

THIS ASSUMES LESSPHP v0.3.8+ Unsure about earlier versions, but you’ll get the gist of how it works if it doesn’t straight out of the box.

<link rel="stylesheet" type="text/css" href="https://stackoverflow.com/questions/12274628/styles/main.less" />

If you were using less.js to compile client side, make sure you change rel="stylesheet/less" to rel="stylesheet"

1) Grab Lessphp I placed these files in /www/compilers/lessphp/ for the context of this demo

2) Make a PHP script that we can throw out LESS files at. This will deal with caching, compiling to CSS and returning the CSS as a response. I have placed this file at /www/compilers/ and called it lessphp.php

Most of this code was on the Lessphp site, except there were errors in it, and I have added the response at the end.

<?php
require "lessphp/lessc.inc.php";
$file = $_GET["file"];
function autoCompileLess($inputFile, $outputFile) {
    // load the cache
    $cacheFile = $inputFile.".cache";
    if (file_exists($cacheFile)) {
        $cache = unserialize(file_get_contents($cacheFile));
    } else {
        $cache = $inputFile;
    }
    $less = new lessc;
    $less->setFormatter("compressed");
    $newCache = $less->cachedCompile($cache);
    if (!is_array($cache) || $newCache["updated"] > $cache["updated"]) {
        file_put_contents($cacheFile, serialize($newCache));
        file_put_contents($outputFile, $newCache['compiled']);
    }
}
autoCompileLess('../' . $file, '../' . $file . '.css');
header('Content-type: text/css');
readfile('../' . $file . '.css');
?>

This will compile the LESS file (eg, styles/main.less) to a cache file and a CSS file (eg, styles/main.less.css).

3) Add a mod_rewrite rule so that any LESS files a user requests are redirected to our compiler, giving it its path. This was placed in the root .htaccess file.

<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteBase /
    RewriteRule ^([^.]*\.less)$ compilers/lessphp.php?file=$1 [R,QSA,L]
</ifModule>

If you are using WordPress, this rule will need to come after it – even if WordPress is in a sub directory, it seems to overwrite these rules, and LESS compilation will not occur for referenced files which exist below (directory wise) WordPress’s .htaccess rules.

4) Your LESS code should be relatively referenced in relation to the compilers location. Additionally, Lessphp compiler will fail if there are empty attributes, eg. background-color: ;

---

If all is working well, the following should occur:

1. Directly browse your LESS file http://domain.com/styles/main.less

2. Be automatically redirected to http://domain.com/compilers/lessphp?file=styles/main.less

3. Be presented with minified CSS

4. main.less.css and main.less.cache should now exist in the same directory as your LESS file

5. The last modified dates shouldn’t change unless you update your LESS file