College of Engineering & CS Wright State University Dayton, Ohio 45435-0001

CEG 333: Introduction to Unix Prabhaker Mateti The Environment String

The environment is the set of string variables available to all processes. The env command displays the environment and the set command manipulates it.

Since all programs can access the environment string, it's frequently used as a way to supply options to commands without repeating them every time the command is invoked. (ls reads LS_OPTIONS, for example).

Other examples of values commonly stored in the environment are:

• HISTSIZE: the number of items to store in ~/.bash_history (or HISTFILE)
• PATH: the path searched for commands by the shell
• PWD: the current working directory
• PS1: the format of the command prompt
• DISPLAY: the computer on which to show X programs

It is a Unix convention that all global environment variable names be upper-case.

In bash, environment variables may be manipulated just like any other shell variable, using $, =, and so forth. For example, PATH=$PATH:~/bin appends the user's own bin directory to the path.