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To write Perl programs, you need two things: a text editor and a Perl interpreter, which you can download very quickly from any number of Web sites, including perl.org, cpan.org, and activestate.com. Unlike with compiled languages, such as C++ and Java, you do not need to first compile your program into machine-readable code before it can be executed. The Perl interpreter does it all; it handles the compilation, interpretation, and execution of your program. Advantages of using an interpreted language like Perl is that it runs on almost every platform, is relatively easy to learn, and is very fast and flexible.
Languages such as Python, Java, and Perl are interpreted languages that use an intermediate representation, which combines both compilation and interpretation. It compiles the user's code into an internal condensed format called bytecode, or threaded code, which is then executed by the interpreter. When you run Perl programs, you need to be aware of two phases: the compilation phase and then the run phase, where you will see the program results. If you have syntax errors, such as a misspelled keyword or missing quote, the compiler will send an error. If you pass the compiler phase, you could have other problems when the program starts running. If you pass both of these phases, you will probably start working on formatting to make the output look nicer or improving the program to make it more efficient, etc.
The interpreter also provides a number of command-line switches (options) to control its behavior. There are switches to check syntax, send warnings, loop through files, execute statements, turn on the debugger, etc. You will learn about these options throughout the following chapters.
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