drush for several drupal
First I assume you have drush 8 since that is required for both D7 and D8.  It's also the default on drush.org.

The best way to deal with multiple Drupal sites is via Drush Aliases.

Basically you create a .drush directory in your home directory and create a aliases.drushrc.php file in it.  For each site, have an entry with the minimum information of:

$aliases['d7'] = array (
  'uri' =&gt; 'yoursite.dev',
  'root' =&gt; '/path/to/drupal/root',
):


There are a lot more options but those are the required ones for local sites.

To use them, run drush commands using the @alias option.  E.g.:

drush @d7 status


This will let you switch between multiple local sites.