Use this function to get a list - as an array - of the loaded Apache modules. Each set up may be different. Here’s the list of available modules for Apache 2.2.

$list = apache_get_modules();
// Your results may vary
/*
array (
  0 => 'core',
  1 => 'mod_log_config',
  2 => 'mod_logio',
  3 => 'prefork',
  4 => 'http_core',
  5 => 'mod_so',
  6 => 'mod_alias',
  7 => 'mod_auth_basic',
  8 => 'mod_authn_file',
  9 => 'mod_authz_default',
  10 => 'mod_authz_groupfile',
  11 => 'mod_authz_host',
  12 => 'mod_authz_user',
  13 => 'mod_autoindex',
  14 => 'mod_cgi',
  15 => 'mod_deflate',
  16 => 'mod_dir',
  17 => 'mod_env',
  18 => 'mod_mime',
  19 => 'mod_negotiation',
  20 => 'mod_php5',
  21 => 'mod_setenvif',
  22 => 'mod_status'
)
*/
See the manual entry for apache_get_modules()