I\'m trying out the PHP micro Framework Lumen (from Laravel).
One of my first steps was to look into the .env.example file and make a copy of it to have my          
        
This answer was inspired by @thomas-venturini 's update to the question. Here's a bash script that takes care of creating .env and updating it with an APP_KEY using the aforementioned PHP command and the UNIX sed command:
#!/usr/bin/env bash
function generate_app_key {
    php -r "echo md5(uniqid()).\"\n\";"
}
APP_KEY=$(generate_app_key)
sed -e s/APP_KEY=.*$/APP_KEY=${APP_KEY}/g .env.example > .env
Hope someone finds this useful.