In development the CSS file is generated on the fly, while the file is stored permanently in the production build script.

less processing with php and symfony2

<?php

//   RewriteRule ^css/main.css$ dev/less/getcss.php?cssfile=main [L]

header("Cache-Control: no-cache");
header('Content-Type: text/css');

if (isset($_GET['cssfile'])) {
    $cache = generatecss($_GET['cssfile']);
    if (isset($cache['compiled']) && is_array($cache)) {
        $data = $cache['compiled'];
    } else {
        $data = $cache;
    }
} else {
    $data = "// cssfile GET parameter missing";
}

echo $data;

function generatecss($cssfile)
{
    $lessCompiler = __DIR__.'/../../src/vendor/lessphp/lessc.inc.php';
    if (!include $lessCompiler) {
        return "// less class definition not found: ".$lessCompiler;
    }

    if (!preg_match('/^[a-z_]+$/i', $cssfile)) {
        return "// cssfile parameter illegal: $cssfile";
    }

    $input = __DIR__."/../../app/$cssfile/config/$cssfile.less";
    if (!file_exists($input)) {
        return "// cssfile input file missing: $input";
    }

    try {
        $cacheDir = __DIR__."/../../app/$cssfile/cache/dev";
        $cacheFile =$cacheDir."/cache_$cssfile.less";
        if (file_exists($cacheFile)) {
            $input = unserialize(file_get_contents($cacheFile));
            $time = $input['updated'];
        } else {
            $time = 0;
        }

        $cache = lessc::cexecute($input);
        if ($time < $cache['updated']) {
            if (!file_exists($cacheDir)) {
                mkdir($cacheDir, 0770, true);
            }
            file_put_contents($cacheFile, serialize($cache));
        }
    } catch (exception $e) {
        return "// While compiling $input, encountered: ".$e->getMessage();
    }

    return $cache;
}