Quote：How to add a Directory to the Path in Linux

Pre and Post Pathing Linux determines the executable search path with the $PATH environment variable. To add directory /data/myscripts to the beginning of the $PATH environment variable, use the following:

PATH=/data/myscripts:$PATH

To add that directory to the end of the path, use the following command:

PATH=$PATH:/data/myscripts
重启Terminal后生效；

若希望设置路径立即生效，可输入：
source .bashrc

Adding to a Single User's Path

To add a directory to the path of a single user, place the lines in that user's .bash_profile file. Typically, .bash_profile already contains changes to the $PATH variable and also contains an export statement, so you can simply add the desired directory to the end or beginning of the existing statement that changes the $PATH variable. However, if .bash_profile doesn't contain the path changing code, simply add the following two lines to the end of the .bash_profile file:

PATH=$PATH:/data/myscripts
export PATH

Adding to All Users' Paths (except root)

You globally set a path in /etc/profile. That setting is global for all users except user root. Typical /etc/profile files extensively modify the $PATH variable, and then export that variable. What that means is you can modify the path by appending or prepending the desired directory(s) in existing statements modifying the path. Or, you can add your own path modification statements anywhere before the existing export statement. In the very unlikely event that there are no path modification or export statements in /etc/profile, you can insert the following 2 lines of code at the bottom of /etc/profile:

PATH=$PATH:/data/myscripts
export PATH

Adding to the Path of User root

User root is a special case, at least on Mandrake systems. Unlike other users, root is not affected by the path settings in /etc/profile. The reason is simple enough. User root's path is set from scratch by its .bash_profile script. In order to add to the path of user root, modify its .bash_profile.

Summary

A fundimental administration task is adding directories to the execution paths of one or more users. The basic code to do so is:

PATH=$PATH:/data/myscripts
export PATH

Place that code, or whatever part of that code isn't already incorporated, in one of the following places:

User Class	Script to modify
One user	$HOME/.bash_profile
All users except root	/etc/profile
root	/root/.bash_profile

export PATH
Quoted from: http://www.troubleshooters.com/linux/prepostpath.htm