Drush 6 installed on a centos server. How do i find out where its installed and upgrade it?

Question

how do i find where is drush installed? its currently on drush 6 and looking to update it to drush 7 for drupal 8. Whats an easy way to find where its installed and update it?

Answer 1

Use which drush to get the installation path of Drush on CentOS:

cat which drush | grep SCRIPT_PATH -m1

which drush will return the path to the drush shell script, which is a readable text file. The SCRIPT_PATH variable in this shell script contains a path to the drush.php file. In the directory, other than this file rest are the files of drush library.

Example:

cat `which drush` | grep SCRIPT_PATH -m1
SCRIPT_PATH=/usr/share/pear/drush/drush.php

To upgrade a drush check this: https://www.drupal.org/node/901828
Also check this one (including comments): https://www.drupal.org/node/1248790

References:
Installing Drush On Any Linux Based Server Out There
Install Drush on CentOS (with H-Sphere)