php - Override core Magento DB connection using environment variables -

i trying use environment variables loaded magento application override default database connection credentials.

i've managed 'almost' working using getenv('my_custom_var'), trying use same method override database credentials, sensitive data can stored within htaccess.

e.g

# .htaccess file  setenv db_username root  setenv db_password password123  setenv db_host localhost 

my app.php (within app/code/local/mage/core/model/app.php - copy of 1 core pool)

// function overrides core 1 protected function _initbaseconfig() {     varien_profiler::start('mage::app::init::system_config');     $this->_config->loadbase();      /* read db connection config environment variables */     $connection = $this->_config->getnode('global/resources/default_setup/connection');     $connection->setnode('host', getenv('db_host'));     $connection->setnode('username', getenv('db_username'));     $connection->setnode('password', getenv('db_password'));      varien_profiler::stop('mage::app::init::system_config');     return $this; } 

i want $connection created default global database connection used site-wide, code should appear if enter pure random entries db_host/db_password etc.. still connects database suggests isn't overriding default database settings configured magento setup.

any ideas on how $connection override , become 'global' database connection?

p.s apologies in advance if question similar previous one, original question bit of general question whereas 1 more focused particular section.

update... have open local.xml within app/etc directory , set 'default setup' database connection inactive (by changing active node value 0) , expected returns error. appear overriding function doesn't seem override initial db connection.. ideas guys?

for mysql db can next:

1. copy file lib/zend/db/adapter/mysqli.php app/code/local/zend/db/adapter/mysqli.php
2. open app/code/local/zend/db/adapter/mysqli.php , find _connect() function.

3. in function near line 317 you'll see:

   $_isconnected = @mysqli_real_connect(
   $this->_connection,
   $this->_config['host'],
   $this->_config['username'],
   $this->_config['password'],
   $this->_config['dbname'],
   $port
   );

4. redefine params:

   $this->_config['host'] = getenv('db_host');
   $this->_config['username'] = getenv('db_username');
   $this->_config['password'] = getenv('db_password');
   

   $_isconnected = @mysqli_real_connect(
   $this->_connection,
   $this->_config['host'],
   $this->_config['username'],
   $this->_config['password'],
   $this->_config['dbname'],
   $port
   );

5. clear cache , restart mysql. other databases check files in lib/zend/db/adapter folder (db2.php, oracle.php, sqlsrv.php).