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...