What does the shell parameter $0 store?

• A. Stores the first word of the entered command (the name of the shell program).
• B. Stores all command line arguments
• C. Stores the exit status of the last command
• D. Stores the PID of the current script

Answer: (A)

The value stored in this shell parameter is the name or path used to invoke the current shell or script—the first word on the command line. That means inside a script, it’s the script’s own filename (or the command used to run it), and in an interactive shell, it’s the shell program itself (for example, bash or sh). This is why you’ll often see $0 used in usage messages or to determine the script’s location relative to its own path.

So this matches the idea of the first word of the entered command, which identifies what was started. It’s not the collection of all arguments (that’s $@ or $*), not the exit status of the last command (that’s $?), and not the process ID (that’s $$).