In this chapter, we discussed many aspects of errors in Bash scripts. First, error checking was described. To start with, we explained that an exit status is a way for commands to communicate whether their execution was considered a success or failure. The test command and its shorthand [[...]] notation were introduced. This command allows us to perform functional checks in our scripts. Examples of this are comparing strings and integers, and checking if a file or directory is created and accessible/writable. We gave a quick refresher on variables, followed by a short introduction to running a script with the debug flag, -x, set.

The second part of this chapter dealt with error handling. We described the (unofficial) if-then-exit construct, which we use to check command execution and exit if it failed. In the examples that followed, we saw that we do not always have to write return code to variables when we want to check them; we can use $? directly in a test case. Going on, we gave a preview of how we can use if-then-else logic to handle errors in a better way. We ended the second part of this chapter by presenting the shorthand syntax for error handling, which we will continue to use throughout the rest of this book.

In the third and final part of this chapter, we explained error prevention. We learned how we can check if the arguments are correct and how we can avoid issues with absolute and relative paths when calling our script. In the final part of this chapter, we answered the question we posed at the beginning: How can we best deal with yes/no input from the user? By using some simple Bash parameter expansions (which will be further explained in the last chapter of this book), we were able to simply facilitate multiple answering styles for the users of our script.

The following commands were introduced in this chapter: mktemp, true, and false.