Normally to add to your $PATH permenantly you do something like this: export PATH=$PATH:/new/dir. You may notice though tht this doesn't always seem to work. Here's an example:

$ export PATH=$PATH:/home/sbrl/bin
$ newcommand # works
$ sudo bash
# newcommand # works
# exit
$ sudo newcommand # doesn't work...wait what?

When a command is run with sudo, it doesn't respect your existing $PATH variable. To change it, you need to open the file /etc/sudoers and add your path to the line that says something like

Defaults    secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin
:/bin"

In order for your folder to be in your $PATH when you use sudo command.