Final answer:
In the UNIX shell, a return code of 0 indicates successful execution. Non-zero exit codes indicate errors or failures.
Step-by-step explanation:
In the UNIX shell, a return code of 0 indicates successful execution. This convention is commonly followed in UNIX systems and is known as the exit status. When a command or program completes successfully, it returns an exit status of 0. On the other hand, if there is an error or failure, a non-zero exit status is returned, indicating the type of error that occurred.
For example, if you run a command like ls to list the files in a directory and it completes without any issues, it will return an exit status of 0. However, if you try to execute a program that does not exist, the shell will return a non-zero exit status, such as 127.
Knowing the exit status can be useful when writing shell scripts, as you can use it to determine the success or failure of a command and take appropriate actions based on that.