Exit on error

Here are a couple of ways to get a script to exit on error if a command fails to run.

Integer test

• This is an integer test, which means it looks for a specific integer. In this example, the zero integer is used. This example will attempt to run COMMAND. Since COMMAND should exit with a value of zero if it succeeds and non-zero if it fails, you can check what the exit value is and use the value to determine what happens next in your script:

#!/bin/bash
COMMAND
if
	[ "$?" -ne "0" ];
then
	echo "FAILURE MESSAGE";
	exit 1;
else
	echo "SUCCESS MESSAGE";
	exit 0;
fi

• Explanation: Let the shell know which interpreter to use #!/bin/bash. Run this command (COMMAND). If the exit value of the command ($?) does not equal (-ne) zero (0) then tell me about it (echo "FAILURE MESSAGE") and exit the script with a status of 1 (exit 1). Otherwise (else), tell me it worked (echo "SUCCESS MESSAGE") and exit the script with a status of 0 (exit 0).
• Example using ls as the command:

#!/bin/bash
ls
if
	[ "$?" -ne "0" ];
then
	echo "FAILURE!";
	exit 1;
else
	echo "SUCCESS!";
	exit 0;
fi

String expression test

• This is a string expression test, which means it looks for a specific string. In this example, the zero string is used. This example will attempt to run COMMAND. Since COMMAND should exit with a value of zero if it succeeds and non-zero if it fails, you can check what the exit value is and use the value to determine what happens next in your script:

#!/bin/bash
COMMAND
if
	[ $? != "0" ];
then
	echo "FAILURE MESSAGE";
	exit 1;
else
	echo "SUCCESS MESSAGE";
	exit 0;
fi

• Explanation: Let the shell know which interpreter to use #!/bin/bash. Run this command (COMMAND). If the exit value of the command ($?) does not (!) equal (=) zero (0) then tell me about it (echo "FAILURE MESSAGE") and exit the script with a status of 1 (exit 1). Otherwise (else), tell me it worked (echo "SUCCESS MESSAGE") and exit the script with a status of 0 (exit 0).
• Example using ls as the command:

#!/bin/bash
ls
if
	[ $? != "0" ];
then
	echo "FAILURE!";
	exit 1;
else
	echo "SUCCESS!";
	exit 0;
fi

Obligatory Happy Ending

And they all lived happily ever after. The end.