Simple, quick way to concatenate, minify, and version static files in a Wordpress theme

.htaccess

# Filename-based cache busting
# taken from https://github.com/h5bp/html5-boilerplate/

# This rewrites file names of the form `name.123456.js` to `name.js`
# so that the browser doesn't use the cached version when you have
# updated (but not manually renamed) the file.

<IfModule mod_rewrite.c>
    Options +FollowSymlinks
    RewriteEngine On

    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteRule ^(.+)\.(\d+)\.(js|css|png|jpg|gif)$ $1.$3 [L]
</IfModule>

build.sh

#!/bin/sh

# Run `bash build.sh` from within the theme's directory whenever 
# you need to perform these tasks.

# A separate `watch.sh` script is better for continuous compilation
# of `.scss` files during development.

# Update any paths as needed. This example relies on all the theme's
# `.scss` files being in a `scss` directory, and all the `.js` files
# being in a `js` directory.


# Concatenate and minify the CSS
# Requires: Sass (Ruby)

END_CSS="style.css"
END_MIN_CSS="style.min.css"
SASS_COMMAND="sass --load-path scss --style"

$SASS_COMMAND expanded scss/style.scss:$END_CSS
$SASS_COMMAND compressed scss/style.scss:$END_MIN_CSS

echo "SCSS-to-CSS build compilation successful"

# Concatenate all JS files to into `site.js`
# Explicitly name and order the files if needed

cat js/*.js > js/site.js

echo "JS concatenation successful"

# Minify the combined JS
# Requires: UglifyJS (Node)

uglifyjs --output js/site.min.js js/site.js

echo "JS uglification successful"

exit 0

functions.php

<?php

/*
 * Check environment
 */

function is_prod() {
    if ( home_url() == '<production-url>' ) {
        return true;
    }
    else {
        return false;
    }
}

/*
 * Basic file versioning
 * Note: probably better to use `md5_file` instead of `filemtime`
 * http://www.php.net/manual/en/function.md5-file.php
 */

function version($filename) {
    // get the absolute path to the file
    $pathToFile = TEMPLATEPATH . '/' . $filename;

    //check if the file exists
    if (file_exists($pathToFile)) {
        $needle = '.';
        // return the versioned filename based on the last modified time
        $versioned = '.' . filemtime($pathToFile) . '.';
        // the position of the last instance of '.'
        $pos = strrpos($filename, $needle);
        if ($pos !== false) {
            // replace and return
            return '/' . substr_replace($filename, $versioned, $pos, strlen($needle));
        }
    }
    else {
        // return the original filename
        return '/' . $filename;
    }
}

?>

header.php

<?php

// other code

// only reference the minified file in production
// version which ever file is referenced
is_prod() ? $cssfile = 'style.min.css' : $cssfile = 'style.css';
echo '<link rel="stylesheet" href="' . get_bloginfo('stylesheet_directory') . version($cssfile) . '">';

?>