Reviewing the Environmental Variables

In Chapter 3, Understanding Variables and Pipelines, I introduced the concept of environmental variables. In this chapter, I’d like to expand on that topic.

We’ve already seen that environmental variables can be used to help customize and control your shell environment. Here’s a table of some of the more common environmental variables:

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Environmental Variable	Purpose
USER	The username of the person who is currently logged into the system.
UID	The User ID number of the logged-in user.
EUID	The Effective User ID number of the user who’s running a certain process.