To add a directory to $PATH,  
sudo vi /etc/paths.d/<pkgname> 
Then add <pkgname path>  as the content of the file.
for example, to add npm into the $path
we type "sudo vi /etc/paths.d/npm
add "/usr/local/lib/node_modules/npm/bin" as content for the file.

http://www.cyberciti.biz/faq/appleosx-bash-unix-change-set-path-environment-variable/