Zero dependency quick check for missing keys within the .env.example

check.php

<?php

function getEnvVariablesFrom($filepath){
    $envContent = file_get_contents($filepath);

    $envVariables = array_filter(
        explode("\n", $envContent), function($value){
            return str_contains($value, "=")
                && $value !== '' 
                && !str_starts_with($value, "#");
        }
    );

    return array_map(function($item){
        return explode("=", $item)[0];
    }, $envVariables);
}

$envVariables = getEnvVariablesFrom('.env');

$exapleVariables = getEnvVariablesFrom('.env.example');

array_values(array_diff($envVariables, $exapleVariables));