Learn Linux Shell Scripting - Fundamentals of Bash 4.4

if-then-exit

As you might recall from the previous chapter, the if-then construct used by Bash is common to (almost) all programming languages. In its basic form, the idea is that you test for a condition (IF), and if that condition is true, you do something (THEN).

Here's a very basic example: if name is longer than or equal to 2 characters, then echo "hello ${name}". In this case, we assume that a name has to be, at the very least, 2 characters. If it is not, the input is invalid and we do not give it a "hello".

In the following script, if-then-exit.sh, we will see that our goal is to print the contents of a file using cat. However, before we do that, we check if the file exists, and if it doesn't, we exit the script with a message to the ...