Drupal Development Environment

Drush stands for Drupal Shell and requires:

• zip
• curl
• composer
• drush

Most likely, you'll already have zip and curl installed, and maybe also composer.

Composer: package manager

upgrade to composer 2

composer self-update

Drush: DRUpal SHell

installation

composer global require drush/drush

or, if the use of drush fails after this, you can specify an older version. Current version was ^10.5.

composer global require drush/drush:9

add to your path

Check the output from the drush install and you'll know where drush is installed. Use the mentioned path to add it to your path:

export PATH="$HOME/.config/composer/vendor/bin:$PATH"

see: https://www.liquidweb.com/kb/install-drush-ubuntu-16-04/