Summary

At the start of this chapter, we explained what a variable was: a standard building block that allows us to store information, which we can reference later. We prefer to use variables for a number of reasons: we can store a value once and reference it multiple times, and if we need to change the value, we only have to change it once and the new value will be used everywhere.

We explained that a constant is a special type of variable: it is defined only once in the beginning of a script, it is not affected by user input, and it does not change during the course of the script execution.

We continued with some notes on variable naming. We demonstrated that Bash is very flexible with regard to variables: it allows many different styles of variable naming. However, we explained that readability suffers if you use multiple different naming conventions in the same script, or between multiple scripts. The best idea is to choose one way of naming variables, and stick with it. We recommended using UPPERCASE for constants, and lowercase_separated_by_underscores for all other variables. This will lessen the chance of conflicts between local and environment variables.

Next, we explored user input and how to deal with it. We gave users of our scripts the ability to alter the outcome of our scripts, a function that is almost mandatory for most real-life functional scripts. We described two different methods of user interaction: basic input using positional arguments, and interactive input using the read construct.

We ended the chapter with a brief introduction to if–then logic and the test command. We used these concepts to create a robust way to handle user input, combining positional arguments with a read prompt for missing information, after presenting the pros and cons of each method used alone. This created a script that could be used both interactively and non-interactively, depending on the use case.

The following commands were introduced in this chapter: read, test, and if.