WeberDev.com has just added to their popular "PHP 101" series today with the release of part 13 - "the Trashman Cometh".
Over the next few paragraphs, I'm going to show you some basic tricks to validate user input, catch "bad" data before it corrupts your calculations and databases, and provide user notification in a gentle, understandable and non-threatening way. To prepare for this exercise, I suggest you spin up a CD of John Lennon singing "Imagine", fill your heart with peace and goodwill towards all men, and take a few deep, calming breaths. Once you've exhaled, we can get going.
They prepare you for the "wonderful" world of input validation by means of form validation examples (one of the most common ways users could abuse your site). They cover checking for things like:
- No value entered
- Value entered is invalid/empty
- A date entered isn't valid
- Using regular expressions
They also touch on a few other validation methods before wrapping it up with some more complete code examples and explainations.