Bash shell script to set up drush to use multiple versions
$ git clone https://github.com/uberhacker/drush-versions.git
$ cd drush-versions
$ chmod +x drush-versions
$ sudo mv drush-versions /usr/local/bin
$ drush-versions
Currently, this script works only in Debian/Ubuntu/RedHat/CentOS and derivative Linux distros.
$ drush-versions [up|update|un|uninstall|-d #|--default #]
For Drupal 5 sites:
$ drush4
For Drupal 6 sites:
$ drush5
For stubborn Drupal 7 sites:
$ drush6
For well-behaved Drupal 7 sites:
$ drush7
For Drupal 8 sites:
$ drush8
For bleeding-edge Drupal 8 sites:
$ drush9
Default version:
$ drush
Update drush to the latest versions:
$ drush-versions update
Change the default to drush version 6:
$ drush-versions --default 6
$ drush-versions uninstall