How to check the exit status code

When a command finishes execution, it returns an exit code. The exit code is not displayed on the screen by default. To examine the exit code, you need to examine a special variable, "$?"

Say, you are searching for a string in a text file.

$ grep x1y2z3 somefile.txt
$

The standard output of the command returns null, which is a pretty good indication that the string cannot be found in the file.

But what if you embed the grep command in a script? How can you tell if the string is found or not?

Checking the exit code will tell you. Let's first try it out interactively.

$ grep x1y2z3 somefile.txt
$ echo $?
1

Note that in bash, the exit status is 0 if the command succeeded, and 1 if failed. For grep, 0 means that the string was found, and 1 (or higher), otherwise.

To check the exit status in a script, you may use the following pattern:

somecommand  argument1 argument2
RETVAL=$?
[ $RETVAL -eq 0 ] && echo Success
[ $RETVAL -ne 0 ] && echo Failure