Checking that a form has been submitted is one of the first things you will encounter when handling form inputs. For arguements sake, here is my example form:

<form action="script.php" method="post">
   <input name="email" type="text" />
   <input name="submit" type="submit" value="Submit">

What the form above will do is post the variables email and submit to the action, script.php.

At this stage most people tend to check to see if a form has been executed by verifying if the submit button variable has been delivered to the receiving script, using code similar to this:

PHP Code:
In most cases this will work, but there are a few occasions when it won't. To identify when this condition will fail we have to look at the different ways of submitting a form.

There are two ways of submitting a form, one is to click the submit button, the other is to hit return, of which will envoke the submit button. The problem occurs when you hit the return button (as most people do), when using Internet Explorer (the most commonly used browser) and when the submit button does not have focus. This will submit the form, but it will not send the submit variable, which would mean the script we are using above will fail.

Despite this flaw, there is an easy solution:

<input type='hidden' name='submit' />
Here we are setting a hidden variable within our form, so no matter how the form is submitted, the submit variable will always be posted, this means there is no requirement to modify how your PHP works.

I hope this helps,

- Create demonstration script