Installing Drush

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Prerequisites

• Basics of Composer

Drupal 8 Drush

Installation of Drush changed permanently in Drupal 8.4.

Using previous versions of Drush and previous versions of Drupal, Drush could be installed globally (via composer require -global drush/drush or similar) and then used within any Drupal Project (though this ended badly) or creating in a directory all alone (see method below) and used via an alias.

With the addition of the Composer and the greater portions of the Symfony Framework, maintaining Drush as a project dependancy was the next logical evolution.

Steps to Install Drush 8.x or Drush 9.x

All of this information can be found at http://docs.drush.org/en/master/install/

To start, the gang at Drush highly recommends installing the Drush Launcher, which allows the drush command to be used globally, even though composer require -global cannot be performed.

$ cd ~/some-drupal-site
$ composer require drush/drush

Most general options for requiring drush are:

$ composer require drush/drush:9.x
$ composer require drush/drush:8.x

Drush 7.x can technically be installed via composer require, but only Drupal 7 and Drupal 8 support Composer. If using Composer within a Drupal 8 project, you're better off with drush 8.x.

Older Versions of Drush

These methods do not work for Drush 9.x and support will degrate for Drush 8.x starting October 2017.

Sometimes it is prudent to maintain multiple versions of Drush, especially when maintaining multiple Drupal sites with different versions of Drupal installed.

For Example:

• Drupal 6 will not work with Drush 8.x or Drush 9.x
• Drupal 7 will work with both Drush 7.x and Drush 8.x
• Drupal 8 will work with both Drush 8.x and Drush 9.x
• The local version of Drush used to connect must be the same as the remote server (7.x, 8.x, etc.)
• The local version of Drush used to connect must be a greater release than the remote server (8.11, 7.1.8, etc.)

Steps to Keep Older Versions of Drush Available

This method is basically just exploiting Composer to keep a version of Drush 'at the ready' when needing to use Drush for Maintenance and upkeep of older Drupal installations.

Install drush 7.x

• mkdir ~/drush7
• cd ~/drush7
• `composer require "drush/drush:7.*"

Install drush 8.x

• mkdir ~/drush8
• cd ~/drush8
• `composer require "drush/drush:8.*"

Create Aliases

Add the following lines to your ~/.bashrc or ~/.bash_profile:

• alias drush7='~/drush7/vendor/bin/drush'
• alias drush7='~/drush8/vendor/bin/drush'

Credit to ccjjmartin for the tips on multiple versions of Drush, compliments of https://github.com/ccjjmartin/setup.environment.