Programming Perl, 4th Edition

Control Structures

So far, except for our one large example, all of our examples have been completely linear; we executed each command in order. We’ve seen a few examples of using the short-circuit operators to cause a single command to be (or not to be) executed. While you can write some very useful linear programs (a lot of CGI scripts fall into this category), you can write much more powerful programs if you have conditional expressions and looping mechanisms. Collectively, these are known as control structures. So you can also think of Perl as a control language.

But to have control, you have to be able to decide things, and to decide things, you have to know the difference between what’s true and what’s false.