How to add custom global variable declarations in Drupal settings.php
We start thinking about global variables when we want something to be available just everywhere. One case is when we want a particular variable to be available to all modules in a site. In Drupal, global variables are usually defined in settings.php. With that, all modules can access that variable.
We can use the $conf array to set those variables in settings.php and the variable_get() function to access those variables from different modules.
For example, once you have added the following in settings.php,
$conf += array(
'MY_TEST_URL' => 'ftp.testsite.com',
'MY_TEST_USERNAME' => 'myuname',
'MY_TEST_PASSWORD' => 'mypassword'
you can use that variable in our modules with the variable_get function as follows:
$my_url_variable = variable_get('MY_TEST_URL');