How can I install Drush without Composer?
This is the simplest solution I have found. 

If you don't want to use composer, follow the instructions here...

https://sharpi.sh/blog/web-development/install-drush-on-ubuntu-quickly-without-composer/


Download a Drush release from Github to user folder


wget https://github.com/drush-ops/drush/releases/download/8.1.17/drush.phar


Rename drush.phar to drush


mv drush.phar drush


Find the bin directory


echo $PATH

which shows something like.... /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games

I’ll go with /usr/local/bin


Move drush to the bin


mv drush /usr/local/bin/drush


Change permissions to


chmod +x /usr/local/bin/drush


Test with


drush version