Every command in bash returns an exit status. Exit statuses are represented as integers ranging from 0 to 255. These integers, however, can be categorised under 2 categories:

• zero exit codes, which represent an exit status that has succeeded. There is only one zero exit code: 0
• non-zero exit codes, which represent an exit status that has failed. Non-zero exit codes have different meanings and are in the range: 1-255
• Read more

Grabbing a command's exit code

You can easily check the exit code of a previous command by using the defined global variable $?. It stores the exit code that the call/command before it returned:

function failure_fn() {
	echo "I will fail"
	return 1
}

function main_fn() {
	echo "Just a regular echo with exit 0 of course"
	echo "$?" # 0

	failure_fn
	echo "$?" # 1
}
main_fn

Using the && and || operator to check exit code

There are two operators which we can use in conjunction with an exit code in our code.

• &&: this only evaluates the right-hand side code if the left-hand side command has a zero exit code
• ||: this only evaluates the right-hand side code if the left-hand side command has a non-zero exit code

The example below will check if a record is in a text file and check if we have an audio playing program:

function can_play_music() {
	if command -v aplay > /dev/null; then
		return 1
	fi
}

function does_have_record() {
	grep -q "$record" my_records.txt && echo "I found the record"
}

function play_record() {
	record="Kind of Blue"
	does_have_record

	record="The Fat of The Land"
	does_have_record || echo "$record not found! Shame on you!"

	can_play_music || exit 1
}
play_record