This is a short introduction to Perl.
Many of the hacks in this book use Perl to process text files. I’m sure that many of you have never used Perl (or any programming language, for that matter), so I want to give a short introduction. This introduction should be enough to let you write really simple programs, to understand the sample programs in this book, and to modify the sample programs to do different things. If you don’t want to understand my scripts, modify my scripts, or write your own scripts, you can safely skip this hack.
Perl programs are usually called Perl scripts because they are interpreted in real time by the Perl program. (Perl is an example of an interpreted language. Other languages you might have heard of, like C++ and Java, are compiled languages. Here’s a quick analogy: suppose the computer is a baker. The Perl program is similar to a recipe to make cake from scratch, and the compiled C++ program is similar to a cake mix. You can bake a cake from either recipe, but the cake mix eliminates steps for you ahead of time.)
This section introduces some basic concepts in Perl, showing constructs we’ll use many times in this book.
Perl statements tell the computer to do something. As a simple example, let’s write a short program to print something:
print "hello world\n";
(Notice the semicolon at the end of the statement. You need to put a semicolon after the end of every statement in Perl. Oh, and the \n means “start a new line.”) If you ...