Built-In Variables

The Linux kernel provides the shell with several built-in variables. You cannot modify the results of these variables. These include

• $# Number of positional parameters passed to the shell (which we used in the last section)

• $? Completion code of the last command or shell program executed within the shell (returned value)

• $0 The name of the shell program

• $* A single string of all arguments passed at the time of invocation of the shell program

These are just a few of the basic tasks and things you can do with your shell. We'll go even deeper in Chapter 33, "Command-Line Master Class."