Unix Power Tools, 3rd Edition

Chapter 4. Interacting with Your Environment

Basics of Setting the Prompt

The prompt displayed by your shell is contained in a shell variable (Section 35.9) called prompt in C-type shells and PS1 in Bourne-type shells. As such, it can be set like any other shell variable.

There are two or three ways to set a prompt. One is a static prompt (Section 4.2) that doesn’t change during your login session (as you change directories, as the time of day changes, etc.). Some shells let you set a dynamic prompt (Section 4.3) string that is interpreted by the shell before each prompt is printed. Even on shells that don’t interpret prompt strings dynamically, you can simulate a dynamic prompt (Section 4.4) by changing the prompt string automatically.^[1]

Depending on your shell’s capabilties, you can use or combine those three techniques — and those found in the rest of this chapter — to do a lot. But, of course, you don’t want to type that prompt-setting command every time you log in. So after you’ve perfected your prompt on the command line, store it in the correct shell setup file (Section 3.3): use the file that’s read by interactive shells or add an interactive shell test to your setup file. (Setting the prompt in noninteractive shells is pointless — and it can even cause problems (Section 4.5).)

—JP, TOR, and SJC

Static Prompts

As Section 4.1 explains, the simplest prompts — which I call static prompts — are prompts whose value are set once. The prompt doesn’t change (until you reset the prompt ...