Linux Command Line and Shell Scripting Bible, 4th Edition

CHAPTER 6Using Linux Environment Variables

IN THIS CHAPTER

• Looking at environment variables
• Creating your own local variables
• Removing variables
• Exploring default shell environment variables
• Setting the PATH environment variable
• Locating environment files
• Using variable arrays

Linux environment variables help define your Linux shell experience. Many programs and scripts use environment variables to obtain system information and store temporary data as well as configuration information. Environment variables are set in lots of places on the Linux system, and it's helpful to know their locations.

This chapter walks you through the world of Linux environment variables, showing where they are, how to use them, and even how to create your own. The chapter concludes with how to use variable arrays.

Exploring Environment Variables

The Bash shell uses a feature called environment variables to store information about the shell session and the working environment (thus the name environment variables). This feature also allows you to store data in memory that can be easily accessed by any program or script running from the shell. It is a handy way to store needed persistent data.

There are two environment variable types in the Bash shell:

• Global variables
• Local variables

This section describes each type of environment variable and shows how to view and use them.

NOTE

Even though the Bash shell uses specific environment variables that are consistent, different Linux distributions ...