Drush install on RedHat 6 seems to do nothing
Easiest way is to use the package manager:

yum -y install php-drush-drush


Alternatively, if it's installed in /usr/local/share then make a symbolic link:

sudo ln -s /usr/local/share/drush/drush /usr/local/bin/drush


Then, verify it works with:

which drush