eBay Hacks, 2nd Edition

Getting Started with the Code in This Book

One of the ways eBay Hacks is different from other eBay books you might’ve read is that the solutions contained herein are not limited to the features available on the eBay web site. Rather, the hacks in this book make use of other websites, third-party software tools, and programming code you can type in, customize, and run yourself.

Tip

You don’t have to type any of the code in this book by hand! Just go to ebayhacks.com, click The Hacks, and select the hack or section in which the code appears.

Some of this code is simple, requiring no prior experience and only a little patience. Depending on the task at hand, though, some other code examples may require some programming experience and a larger amount of the aforementioned patience. (Each hack is adorned with a little thermometer to indicate its complexity, as described in “Conventions Used in This Book,” later in this preface.) What follows is a little background on the languages and concepts used in the hacks that employ code.

eBay’s home is the Web, a heterogeneous place governed by well-defined standards. In most cases, the concepts presented in this book work with any programming language or platform you might be using with your web site. However the example code is primarily kept to three language and platform combinations, each inhabiting its own niche of the Internet ecology: HTML for creating web content, JavaScript for adding interactivity to web pages, and Perl for server-side (CGI) scripting. Programming for the eBay API is a somewhat different animal and is discussed in the introduction to Chapter 8.

HTML

HTML (Hypertext Markup Language) isn’t so much a programming language as a schema used to add formatting to plain text. As a seller on eBay, you use HTML tags to dress up your auction descriptions and to create web content.

You don’t need to be proficient in HTML to start using it; see “Format the Description with HTML” [Hack #52] for an introduction and crash course. The more HTML you know, the more of it you can employ to enhance your listings.

JavaScript

JavaScript is a scripting language (not to be confused with the Java programming language) used to add interactivity to otherwise-static web pages. For instance, when you click thumbnail photos in some eBay auctions to view their larger versions right on the same page, you’re running JavaScript code embedded in the auction page. JavaScript comes in handy if you want to construct an interactive photo album [Hack #79] with photos hosted on your own server [Hack #76] , for example.

JavaScript code is placed within <script></script> tags on an HTML-formatted web page, such as the description in an eBay listing. When someone views your auction, the JavaScript code is executed by the browser client (e.g., Internet Explorer, Mozilla Firefox), which is why it’s categorized as client-sidescripting.

Tip

If you want to use the same JavaScript code in all your eBay listings, you can place the code in a file on your web server (say, scripts.js), and then merely reference it by placing the following line in your listing descriptions:

<script src="http://www.your.server/scripts.js"> </script>

where http://www.your.server/your-scripts.js js the full URL of your scripts.js file. Any JavaScript code in this book that appears inside a <script></script> structure can be used in this way; just remove the opening <script><!--and closing --></script> tags, and you’re good to go!

eBay imposes some restrictions on the use of JavaScript in listing descriptions, presumably in an effort to reduce the risk of abuse. Among the more useful JavaScript elements specifically prohibited in descriptions are the window. open statement and eval() function. If you try to submit a listing containing one of these prohibited statements, you’ll get this confusing and largely inaccurate error message:

Your listing cannot contain javascript (“.cookie”, “cookie(“, “replace(“, IFRAME, META, or includes), cookies or base href.

Although none of the code in this book uses these forbidden statements, it is entirely possible that eBay may have introduced additional restrictions by the time you read this. As with all the code in eBay Hacks, be sure to visit ebayhacks.com for any applicable corrections, updates, or workarounds.

Tip

If you’re using Firefox or Mozilla, you can use the JavaScript Console to see error messages and warnings generated by your JavaScript code as you test it. To open the JavaScript Console window, type javascript: (including the colon) in the address bar and press Enter. If you’re using Internet Explorer, you can get something similar by downloading the Microsoft Script Debugger (available for free from www.microsoft.com/downloads/).

Note that there are other ways to add interactivity to web pages, such as VBScript, Java, and (now deprecated) ActiveX controls, but none are as widely supported and seamless as JavaScript.

Perl

In order to show up-to-date information on a web page, such as the current price and the amount of time left on an eBay auction page, its content must be dynamically generated. In most cases, this is done by a program on the web server before the page is sent to the browser. Although just about any programming language is capable of generating web content, most of the hacks in this book use Perl for this purpose. See the “Using CGI Scripts” sidebar for details.

Perl (Practical Extract and Report Language) is a great choice for “server-side” scripting because it’s simple, easy to learn, requires no expensive or complicated development environment, and works on any computing platform. If you’re using Unix, Linux, or Mac OS X, Perl is almost certainly already installed on your system. If you’re using Windows, you can get ActiveState’s ActivePerl for free at www.activestate.com/Products/ActivePerl/.

Using CGI Scripts

Every web server has a dedicated folder (directory) in which scripts or programs are placed. Instead of displaying the contents of the scripts, as would happen with ordinary HTML files, the web server software runs the scripts and displays their output instead. This special script directory is typically called cgi-bin, wherein CGI stands for “common gateway interface. “Refer to your web server software’s documentation for details on setting up a cgi-bin directory, or contact your administrator (ISP) if you’re renting space on someone else’s web server.

Now, copying the Perl scripts discussed throughout this book into your cgi-bin directory is easy enough; the hard part can be making them work.

Provided that the scripts are in the correct location, all you need to do on Unix systems is to make them executable, like this:

chmod +x gallery.pl

where gallery.pl is the filename of the script.

On Windows systems, each Perl script must have a filename that ends with .pl. Then, you’ll need to associate the .pl filename extension with your Perl interpreter. In most cases, this will be done for you when you install Perl.

The last step is to reference the script with the proper URL, like this:

http://www.ebayhacks.com/cgi-bin/gallery.pl

where www.ebayhacks.com is the address of your server, cgi-bin is the public name of your cgi-bin directory (not always the same as the private name), and gallery.pl is the filename of your script. If all goes well, you should see the output of the script in your web browser. (It’s important to note that not all Perl scripts in this book are CGI scripts.)

If you get an error when you try to run the script from your browser, try running it from the command line instead to see more-detailed error messages.

Tip

Some hacks in this book require the use of Perl modules, extensions to the Perl language that add functionality you’d otherwise have to program from scratch. See the “Installing Perl Modules” sidebar for details.

Perl scripts are simply text files; you can edit them with any plain-text editor, such as Notepad in Windows or emacs in Unix. (Note that word processors, such as Word and Wordperfect are not suitable for this task, as they’ll jumble up the text file with proprietary formatting data.)

Installing Perl Modules

(Adapted from Google Hacks by Tara Calishain and Rael Dornfest)

A few hacks in this book make use of add-on Perl modules, useful for turning dozens of lines of messy code into a couple of concise commands. If your Perl script resides on a server maintained by someone else (typically an ISP administrator), you’ll have to request that they install the module before you can reference it in your scripts. But if you’re the administrator, you’ll have to install it yourself:

Installing on Unix, Linux, and Mac OS X. Assuming you have the CPAN module, have root access, and are connected to the Internet, installation should be no more complicated than:

% su

% perl -MCPAN -e shell

cpan> install WWW::Search::Ebay

Note that capitalization counts; copy-and-paste the module name for an exact match. If the install fails, you can try forcing an installation by typing:

cpan> force install WWW::Search::Ebay

Go grab yourself a cup of coffee, meander the garden, read the paper, and check back once in a while. Your terminal’s sure to be riddled with incomprehensible gobbledegook that you can, for the most part, summarily ignore. You may be asked a question or three; in most cases, simply hitting Return to accept the default answer will do the trick.

Installing on Windows. If you’re running Perl under Windows, you’ll need the Programmer’s Package Manager, which is incedentally included with ActiveState’s ActivePerl distribution. (If you don’t have it, you can get it at aspn.activestate.com/ASPN/Downloads/ActivePerl/PPM/.) PPM grabs nicely-packaged module bundles from the ActiveState archive and drops them into place on your Windows system with little need of help from you. Simply launch PPM from inside a Command Prompt window (Start → Run → cmd.exe) and tell it to install the module:

C:\>ppm

PPM> install WWW-Search-eBay

At this point, installation proceeds just like Unix, discussed above.

Once a Perl module has been successfully installed, you can reference it from your Perl programs.

To run a Perl script in Windows, as long as filename has the .pl file extension,* you can double-click the file icon to start Perl and execute the script. If the script provides text output, you’ll want to run it from a Command Prompt window (Start → Run → cmd.exe) instead; just go to the folder containing the script (type cd foldername), type the name of the script file, and press Enter.

To run a Perl script in Unix, Linux, or Mac OS X, open a terminal window, go to the folder containing the script (cd foldername), type ./scriptfilename (where scriptfilename is the filename of the script), and press Enter.

If you want to learn more about Perl, the book to get is Programming Perl, Third Edition (also known as the “Camel Book”) by Larry Wall, Tom Christiansen, and Jon Orwant.