web development

Controlling Program Flow

27 January 2005 / Leave a Comment

Normally when you run a Perl script, the computer moves through each line of your script in turn, executing each line as it goes. However, often you’ll want to alter this flow through the script.

For example, you might want to run different pieces of code depending on whether a visitor has filled out a form correctly or not. Also, you often want to run the same piece of code lots of times – for example, when reading through each line of a file.

Perl features a number of useful ways to alter the path of execution through your script. In this tutorial I’ll show you the most common techniques, and how you can use them.

Working with Files

7 July 2003 / 3 Comments

Perl’s filesystem functions let you manipulate files and directories on the server from within your CGI scripts. This means that you can:

store data in files on the server
allow visitors to upload files to your site
create message boards and guestbooks

…and all sorts of other useful stuff!

In this tutorial, we’ll show you how to create files and write to them, how to read from them, how to delete them, and how to scan directories (folders) so that you can see what files are on the server.

We’ll also discuss file and directory permissions, and the concept of full paths. At the end of the tutorial you’ll find a useful script to help you work out your full paths (essential for working with files).

This tutorial will also touch on some other Perl concepts such as while loops, lists, and appending strings to variables. It’s quite a long tutorial, but worth sticking with. By the end of it you’ll have learnt a lot of useful concepts, and you’ll be able to write your own CGI scripts to read and write files on your server!

[Read more…] about Working with Files

Form Validation with Perl and CGI

12 June 2003 / 13 Comments

In this tutorial we’re going to write a CGI script that checks whether a form has been filled out correctly. Along the way, you’ll also learn about the concepts of reentrant forms and Perl subroutines. Read on!

Troubleshooting CGI Scripts

14 May 2003 / 2 Comments

If you’ve tried running a few CGI scripts on your Web server, you’ve probably come across a few problems now and again. Usually, when your script has a problem, you will see an error message similar to the following in your Web browser:


Internal server Error

The server encountered an internal error
and was unable to complete your request.

It’s not a very helpful message, is it! Fortunately there are ways to find out the exact cause of your script error. In this tutorial we look at methods that you can use to troubleshoot your scripts, and also list some common causes of CGI errors.

JavaScript and Cookies

31 October 2002 / 9 Comments

A great feature of JavaScript is that it lets you set and retrieve browser cookies. In this tutorial I’ll show you how this is done, along with a simple example that remembers your name and displays it on every page.

JavaScript Events and Event Handlers

11 December 2001 / 3 Comments

In this tutorial we’re going to take a look at a very handy feature of JavaScript called events. By writing code that reacts to events, you can make your web pages much more interactive!

Read on to find out how…

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