Understanding Exit Codes

You’ve already seen some examples of using the exit command, which can either terminate a script normally or cause it to terminate early upon an error condition. What I haven’t explained yet, is about exit codes. There are two general classes of exit codes, which are:

• Standard shell exit codes: Each shell has its own defined set of exit codes. (To keep things simple, I’ll just talk about bash exit codes in this chapter.)
• User-defined exit codes: You can also define your own exit codes for different purposes.

Let’s talk about standard exit codes first.

Standard Shell Exit Codes

When a program or script runs successfully, it returns an exit code of 0. Otherwise, the exit code will be a non-0 number from 1 to 255. To demonstrate, use find to search through the /etc/ directory for the passwd file, like so:

[donnie@fedora ~]$ find /etc -name passwd
find: '/etc/audit': Permission denied...