$dsn = "DBI:mysql:database=$database;host=$hostname;port=$port"; 

$dsn = "DBI:mysql:test;mysql_read_default_file=/home/foo/my.cnf";

$dsn = "DBI:mysql:test;mysql_socket=/dev/mysql"; 
  
$dbh = DBI->connect($dsn, $user, $password, {'RaiseError' => 1} );