Working with Variables

Variables in the bash shell are words or strings of text that computers use to represent a piece of data. An example of using a variable is setting the variable fruit to contain the text apple. A number of standard variables contain information about your account and environment settings.

Variables versus environment variables

The first thing I need to make clear is that the bash shell has two types of variables:

Variables: A variable can be referenced in a program or shell session, but it’s visible and available to only that session or program.
Environment variables: An environment variable can also be referenced by the shell or program. However, it has the added behavior of having its value copied to any other program or shell that is created from its environment.

You can usually tell at a glance the difference between a variable and an environment variable in bash. The normal convention is to name local variables in all lowercase or in mixed-case characters. An environment variable, however, is usually always in all uppercase letters.

Checking out commonly used environment variables

The bash shell has many environment variables. You may be amazed at the range of items these variables store. The handy thing is that, if something is stored in a variable, you can change it to suit your needs! In Table 6-1, I list the environment variables you’re most likely ...

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