2.3 Installing Perl on Your Computer

The following sections provide pointers for installing Perl on the most common types of computer systems.

2.3.1 Perl May Already Be Installed!

Many computers—especially Unix and Linux computers—come with Perl already installed. (Note that Unix and Linux are essentially the same kind of operating system; Linux is a clone, or functional copy, of a Unix system.) So first check to see if Perl is already there. On Unix and Linux, type the following at a command prompt:

$ perl -v

If Perl is already installed, you'll see a message like the one I get on my Linux machine:

This is perl, v5.6.1 built for i686-linux

Copyright 1987-2001, Larry Wall

Perl may be copied only under the terms of either the Artistic License or the
GNU General Public License, which may be found in the Perl 5 source kit.

Complete documentation for Perl, including FAQ lists, should be found on
this system using 'man perl' or 'perldoc perl'.  If you have access to the
Internet, point your browser at http://www.perl.com/, the Perl Home Page.

If Perl isn't installed, you'll get a message like this:

perl: command not found

If you get this message, and you're on a shared Unix system at a university or business, be sure to check with the system administrator, because Perl may indeed be installed, but your environment may not be set to find it. (Or, the system administrator may say, "You need Perl? Okay, I'll install it for you.")

On Windows or Macintosh, look at the program menus, or use the find program to search for perl. You can also try typing perl -v, at an MS-DOS command window or at a shell window on the MacOS X. (Note that the MacOS X is a Unix system!)

2.3.2 No Internet Access?

If you don't have Internet access, you can take your computer to a friend who has access and connect long enough to install Perl. You can also use a Zip drive or burn a CD from a friend's computer to bring the Perl software to your computer. There are commercial shrink-wrapped CDs of Perl available from several sources (ask at your local software store) and several books such as O'Reilly's Perl Resource Kits, include CDs with Perl.

Apart from installing Perl, you don't need Internet access for everything in this book. If you want to do the exercises while commuting on the train, or whatever, it can certainly be done. Apart from installing Perl, the main use of the Internet for this book is to download its examples from the book's web site without having to type them; to download and try the exercises; to explore biological data from various biological databases; and to access Perl documentation, if it's not installed on your machine.

Know that if you want to do bioinformatics, the Internet is a practical necessity. You can learn programming fundamentals from this book without an Internet connection, but you will need Internet access to download bioinformatics software and data.

2.3.3 Downloading

Perl is an application, so downloading and installing it on your computer is pretty much the same as installing any other application.

The web site that serves as a central jumping off point for all things Perl is http://www.perl.com/. The main page has a Downloads clickable button that guides you to everything you need to install Perl on your computer. At the Downloads page, there's a Getting Help link and other links. So even if the information in this book becomes outdated, you can visit the Perl site and find all you need to install Perl.

Downloading and installing Perl is usually quite easy, in fact, the majority of the time it's perfectly painless. However, sometimes you may have to put some effort into getting it to work. If you're new at programming, and you run into difficulties, you should ask for help from a professional computer programmer, administrator, teacher, or someone in your lab who already programs in Perl.

So, in a nutshell, here are the basic steps for installing Perl on your computer:

1. Check to see if Perl is already installed; if so, check the that version is at least Perl 5.

2. Get Internet access and go to the Perl home page at http://www.perl.com/.

3. Go to the Downloads page and determine which distribution of Perl to download.

4. Download the correct Perl distribution.

5. Install the distribution on your computer.

2.3.4 Binary Versus Source Code

When downloading from the http://www.perl.com site, you need to choose between binary or source-code distributions of Perl. The best choice for installing Perl on your computer is to get an already made binary version of the program, because it's the easiest to install. However, if no binary is available, or if you want to control the various options of your Perl installation, you can get the source code for Perl, which is itself written in the C programming language. You then compile it using a C compiler. But try to find a binary for your particular computer's operating system; compiling from source code can be complicated for beginners.

2.3.5 Installation

The next sections provide specific installation instructions for specific platforms.

2.3.5.1 Unix and Linux

If Perl isn't installed on your Unix or Linux machine, first try to find a binary to install. At the Downloads page of http://www.perl.com, you'll see the subheading Binary Distributions. Select Unix or Linux, and then see if your particular flavor of operating system has a binary available. Several versions are available, and the web-site instructions should be enough to get Perl installed once you've downloaded the binary. Most versions of Linux maintain up-to-date Perl binaries on their web sites. For instance, if you have a Red Hat Linux system, you need to identify which version of the system you have (by typing uname -a) and then get the appropriate rpm file to download and install. Red Hat has an rpm for Perl that Red Hat Linux users can install by typing:

rpm -Uvh perl.rpm 

(the actual name of the perl.rpm file varies).

If no binary version of Perl is available for your flavor of Unix or Linux, you must compile Perl from its source code. In this case, starting from the Perl web page, click on the Downloads button and then select Source Code Distribution. The source code has an INSTALL file with instructions that guide you through the process of downloading the source code, installing it on your system, compiling the source code into a binary, and finally installing the binary.

As mentioned previously, compiling from source code is a considerably longer process than installing an already made binary, and requires a bit more reading of instructions, but it usually works quite well. You will need a C compiler on your computer to install from source code. Nowadays, some Unix systems ship without a complete C compiler. Linux will always have the free C compiler called gcc installed, and you can also install gcc on any Unix (or Windows, or Mac) system that lacks a C compiler.

2.3.5.2 Macintosh

The MacPerl installation steps are clearly explained on the MacPerl web page, http://www.macperl.com/ (which you can also get to from the Perl web page and its Downloads button). Here's a very brief overview.

From the MacPerl page, click on Get MacPerl, and follow the directions to download the application. It will appear on your desktop. Double-click it to unstuff it. If you don't have Aladdin Stuffit Expander (most Macs already do), this won't work, and you'll have to go to http://www.aladdinsys.com to download and install Stuffit.

MacPerl can be installed as a standalone application under the MacOS Finder or as a tool under the Macintosh Programmer's Workbench; you will probably want the standalone application. Perl Version 5 is available for MacOS 7.0 and later. Details about which Perl version is available for your particular hardware and MacOS version are available at the MacPerl web page.

2.3.5.3 Windows

Several binaries for different Windows versions are available. Since Windows is closely coupled with Intel 32-bit chips, these binaries are often called Wintel or Win32 binaries. The current standard Perl distribution is ActivePerl from ActiveState, at http://www.activestate.com/ActivePerl/, where you can find complete installation directions. You can also get to ActivePerl via the Downloads button from the Perl web site. Under the subheading Binary Distributions, go to Perl for Win32, and then click on the ActivePerl site.

From the ActiveState web site's ActivePerl page, click the Downloads button. You can then download the Windows-Intel binary. Note that installing it requires a program called Windows Installer, which is available at ActivePerl if it's not already on your computer.