Adding or Changing Variables
After you’ve poked around in your environment, you might determine that you want to set a variable that’s currently not available or change one to make it better meet your needs. In general, you won’t randomly specify variables; you’ll do it because a certain program requires a specific variable in order to run.
Variables You Can Mess With
The following table includes some of the variables you can safely change. Keep in mind that the shell itself might not use a specific variable, like NNTPSERVER, while programs running under the shell might. Sometimes shells assign default variables, while in other cases you’ll have to manually set the value.