Using this script you can minify the CSS and JS files.

minify-css-js.sh

#!/bin/bash

#require: uglifyjs and uglifycss npm package
# https://www.npmjs.com/package/uglify-js
# https://www.npmjs.com/package/uglifycss

#Start JS minification
read -p 'Enter the unminified JS directory absolute path: ' JS_DIR

echo "Creating the minified directory...";
mkdir -p $JS_DIR/minified;

for f in `find $JS_DIR/ -type f  -name "*.js" ! -name "*.min.*"`;

do 
    FILE_BASENAME=`basename $f .js`
    echo "Minifying the {$f} file.";
    uglifyjs $f -o $JS_DIR/minified/$FILE_BASENAME.min.js
done;



#Start CSS minification
echo "Do you want to minify the CSS files? [Y,n]"
read input

if [[ $input == "Y" || $input == "y" ]]; then

    read -p 'Enter the unminified CSS directory absolute path: ' CSS_DIR

    echo "Creating the minified directory...";
    mkdir -p $CSS_DIR/minified;

    for f in `find $CSS_DIR/ -type f  -name "*.css" ! -name "*.min.*"`;

    do 
        FILE_BASENAME=`basename $f .css`
        echo "Minifying the {$f} file.";
        uglifycss $f --output $CSS_DIR/minified/$FILE_BASENAME.min.css
    done;
else

  echo "EXIT!"

fi