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Exit Codes

Exit codes (sometimes called "return codes" or "status codes") are how programs communicate back whether they ran successfully or not.

0 is the exit code for success. Any other exit code is an error. 9 times out of 10, if a non-zero exit code is returned (meaning an error) it will be 1, which is the "catch-all" error code.

Programs that call other programs use error codes to figure out if execution was successful. For example, if the Boot.dev server program exits with a non-zero exit code, we have another program that will automatically restart it and log the error.

Printing Exit Codes

In a shell, you can access the exit code of the last program you ran with the question mark variable ($?):

cat greeting.txt
# General Kenobi!
echo $?
# 0

cat file/that/does/not/exist.txt
echo $?
# 1

Running Commands Conditionally

You can run multiple commands on a single line by separating them with a semicolon (;):

command1 ; command2

If you only want the second command to run when the first command succeeds (exit code 0), use &&:

command1 && command2

Assignment

Run the worldbanc/private/bin/warn.sh script without setting the two environment variables (WARN_MESSAGEandWARN_FROM_NAME) that it requires.
Print the exit code (remember, any non-zero exit code is usually considered an "error").

Submit the shell checks.