Webmaster in a Nutshell, Second Edition

Chapter 6. Forms

Most CGI programs use HTML forms to gather user input. Forms are comprised of one or more text-input boxes, clickable radio buttons, multiple-choice checkboxes, and even pull-down menus and clickable images, all placed inside the <form> tag. Within a form, you may also put regular body content, including text and images. The JavaScript event handlers can be used in various form elements as well, providing a number of effects such as testing and verifying form contents.

The <form> Tag

You place a form anywhere inside the body of an HTML document with its elements enclosed by the <form> tag and its respective end tag </form>. All of the form elements within a <form> tag comprise a single form. The browser sends all of the values of these elements--blank, default, or user-modified—when the user submits the form to the server.

The required action attribute for the <form> tag gives the URL of the application that is to receive and process the form’s data. A typical <form> tag with the action attribute looks like this:

<form action="http://www.oreilly.com/cgi-bin/update" >
...
</form>

The example URL tells the browser to contact the server named www.oreilly.com and pass along the user’s form values to the application named update, located in the cgi-bin directory.

The browser specially encodes the form’s data before it passes that data to the server so it does not become scrambled or corrupted during the transmission. It is up to the server to either decode the parameters ...