The Linux Command Line

Chapter 27. Flow Control: Branching with if

In the last chapter, we were presented with a problem. How can we make our report-generator script adapt to the privileges of the user running the script? The solution to this problem will require us to find a way to “change directions” within our script, based on the results of a test. In programming terms, we need the program to branch.

Let’s consider a simple example of logic expressed in pseudocode, a simulation of a computer language intended for human consumption:

X = 5

If X = 5, then:

Say “X equals 5.”

Otherwise:

Say “X is not equal to 5.”

This is an example of a branch. Based on the condition “Does X = 5?” do one thing: “Say ’X equals 5.’” Otherwise do another thing: “Say ’X is not equal to 5.’”

Using ...