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.

In a shell, you can access the exit code of the last program you ran with the question mark variable ($?). For example, if you run a program that exits with a non-zero exit code, you can see what it was with the echo command:

ls ~
echo $?
# 0

ls /does/not/exist
echo $?
# non-zero (depends on your OS)

Assignment

Commands will usually exit with error codes if they've been run without the proper arguments or configuration. For example, the private/bin/warn.sh script will exit with a non-zero code if you don't have the required environment variables set.

Run the warn.sh script without setting the two environment variables (WARN_MESSAGE and WARN_FROM_NAME) that it requires.
Run the echo command to see the exit code.

Paste just the exit code in the text box and submit your answer.

Tips

You can use the unset command to unset an environment variable:

unset ENV_VAR_NAME

Alternatively, you can set the environment variable to an empty string:

export ENV_VAR_NAME=""