What is cgi and how to use your cgibin cgi tutorialpdf
This article describes how to create and process simple web input forms. No other special tools are required. They are not repeated here. The examples shown in this article have been kept simple to make what is cgi and how to use your cgibin cgi tutorialpdf easy to learn. More elaborate web forms, such as multiple-page forms, will be covered in separate articles.
If you want the examples shown here to work properly, please upgrade to a more recent version of REBOL. Comments or corrections to this article should be sent to our feedback page. Web forms are easy to create using a web authoring tool or by typing the necessary HTML tags directly into a text editor and displaying them using a web browser.
Here is the HTML code for creating a very simple form that includes a single text entry field and a submit button:. Save this HTML code to a file called simple. It should look like this:. If your web page does not look like this, check your HTML for errors. The most common mistakes for beginners are:. It displays a web page that shows you the values of the input fields submitted in the form. As a test, enter some text into the form and press the Submit button.
You should see a response from the www. This section expands on that to show how scripts are used to process web forms. Now save the file and view it in your HTML browser.
Type some text and hit the submit button. You will see a web page that looks like this:. As you can see, the CGI object includes information about the web server name and version, the CGI request method, the CGI script path, the data that was submitted query-stringthe browser's IP address remote-addrand much more. In other words, everywhere we show:. See the A Beginner's Tutorial and Guide for more information. The CGI object contains a lot of information. Some of this may be useful to your script, but what you want most is to get the results that were submitted in the web form as shown earlier.
You can easily revise the above script to show it:. When you see the results of the script above, you will notice that the web form data is specially what is cgi and how to use your cgibin cgi tutorialpdf to allow it to be passed back to the CGI script.
I will not describe the CGI encoding method here, but if you are interested you can find information about it here. For example the CGI data:. This will be described in more detail below. It is safe to use just letters alphabet or letters followed by numbers, but do not start a word with a numeric digit and avoid using special punctuation other than a dash "-" within a word.
Note that most of this script is used to create the HTML to be displayed by your web browser. Here is a summary of the script:. You may have noticed these long URLs when you use a web browser to visit various web sites, such as search engines. The data is then read by your program from the query-string field of the CGI object as shown earlier. The solution to this problem is the subject of the next section. This method directs the data to the standard input port of the CGI script, allowing your CGI script to read it directly.
This tells the web server to redirect the query string what is cgi and how to use your cgibin cgi tutorialpdf the CGI script's input port, where it can be read. This reads the web data from the input port and appends each chunk of data to a DATA string.
All of the examples that follow will include this function. This HTML form includes text fields, radio buttons, checkboxes, a dropdown menu, a text area, and a submit button. Yes No Maybe Status? The HTML code for this form is:. The form above can be tested in what is cgi and how to use your cgibin cgi tutorialpdf same way as the earlier examples by sending it to the test. Note that the POST method is used to allow the input fields to be of any length.
Because CGI scripts run on the web server and must be uploaded each time or edited remotely using a shellit can often take a lot what is cgi and how to use your cgibin cgi tutorialpdf time to work out the bugs. One helpful technique is to add a line of code to your CGI script that prints out the query string that was sent to it from the web browser. That way you know for sure what what is cgi and how to use your cgibin cgi tutorialpdf input data is when script begins to process it.
Now, when you run the script, you'll see the "raw" CGI data at the top of your resulting web page. Note that some web browsers may not show it to you unless you view the HTML source to the page. You can also save a lot of time by testing your scripts locally before uploading them to your web server. To provide test data to your script, you can set the CGI object fields directly within your script.
For example, the code below will detect that your script is running locally and supply some test data:. However, the method that I prefer is to modify the READ-CGI function to provide a default return value if the request-method was not found which means the script is running locally, not on the server. Just cut and paste the output as your input for the local test. If a field has multiple return values for a single name as commonly done for checkbox fieldsthe result may be a string or a block.
If you want to be sure that the object always has all its required fields because that may depend on the fields the user submitted in the web form what is cgi and how to use your cgibin cgi tutorialpdf, you can specify a template when you use CONSTRUCT:. Now your script can check object fields to determine if they have been set before accessing them:.
If you did not provide such an object template, and the command field was not provided in the submitted data, your CGI script would error out quit. Probably the most difficult part of writing most CGI scripts is checking the web form fields to make sure that they are valid before processing.
For example, you might require a valid email address, integer number, URL, etc. For example, if a field must contain only numeric digits, you can use code such as:. Another way to check results for fixed values, like those returned from radio buttons or text fields, is to use the FIND function:. Here is a check for a valid integer:. It is a common practice to trim leading and trailing whitespace from text input fields. This is more of a convenience to your web form users.
Note that TRIM modifies its input string value so no assignment of the result is needed. Add a COPY if you don't want this side effect. Depending on your requirements, there are many ways to save your web form data within your CGI script. See the A Beginner's Tutorial and Guide. You can also add fields like the date, requesting computer's IP address, and anything else you need:. The problem comes from the fact that a single CGI script may be run multiple times by the web server at the same time.
If you keep a "counter" in a file to use for generating file names, you create a "race" condition. Two scripts that are running at exactly the same time might read the same counter value before it can be changed. Another method is to use the current date and time to create a file name. This does not work either, because you have the same race condition.
Two scripts may run at exactly the same time and use the same date value. In fact, by using REBOL's graphical user interface you can create forms that are more dynamic and can be validated before sending them to the server resulting in better performance and less traffic on your server and network.
Watch out for data submitted with web forms. Never assume that the data is what you think it is. For example, a name field may not be a name at all, but just random data or data that is intentionally trying to break your CGI script or hack into your server. In order to save data from your forms, your CGI script probably has read-write access to one or more file directories on your server.
You need to be careful. You do not what is cgi and how to use your cgibin cgi tutorialpdf to accidentally give a web user the ability to read other data files or, even worse, to write to any file.
As an extreme case imagine what would happen if a web user, by finding a flaw in your CGI script, could write to an executable file in your CGI directory. The next time that file is executed, a serious problem could result. The best way to avoid such problems is to never allow the data from a web form to provide the file name that is used to access files on the server, unless you check the file path carefully.
For example, you can add a few lines to the top of your script before it accesses files:. If for any reason your CGI script attempts to read or write files outside the "cgi-data" directory or tries to read any files in the "cgi-data" directory, the script will automatically terminate.
For example, as shown earlier, use a command line such as:. If you are sharing your web server with other users such as on a web hosting servicebe aware that CGI directories, scripts, data, and other files may be accessible to other users of the system, depending on your host server's configuration. If this possibility concerns you, check with your server administrator or web service provider for information on how to properly protect your CGI scripts and data.
The HTML code for this form is: Here is an example response from the test. About Contact Support Privacy License.
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