Read cgi files

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 the 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 fields , the 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 , 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. If this program doesn't work, move to Step 3. The file type can give you a clue as to which programs can open your cgi file. Files with the cgi extension are usually Uncommon Files. Once you know the file type, you can use this information do some searching for other possible programs that utilize file extension cgi or that open Uncommon Files.

The value attribute of the instance yields the string value of the field. The getvalue method returns this string value directly; it also accepts an optional second argument as a default to return if the requested key is not present. If the submitted form data contains more than one field with the same name, the object retrieved by form[key] is not a FieldStorage or MiniFieldStorage instance but a list of such instances.

Similarly, in this situation, form. If you expect this possibility when your HTML form contains multiple fields with the same name , use the getlist method, which always returns a list of values so that you do not need to special-case the single item case. For example, this code concatenates any number of username fields, separated by commas:. If a field represents an uploaded file, accessing the value via the value attribute or the getvalue method reads the entire file in memory as bytes.

This may not be what you want. You can test for an uploaded file by testing either the filename attribute or the file attribute. You can then read the data from the file attribute before it is automatically closed as part of the garbage collection of the FieldStorage instance the read and readline methods will return bytes :.

FieldStorage objects also support being used in a with statement, which will automatically close them when done. If an error is encountered when obtaining the contents of an uploaded file for example, when the user interrupts the form submission by clicking on a Back or Cancel button the done attribute of the object for the field will be set to the value When this occurs, the item will be a dictionary-like FieldStorage item.

In this case, it can be iterated over recursively just like the top-level form object. In this case, the list , file , and filename attributes are always None. Changed in version 3. This section describes a higher level interface which was added to this class to allow one to do it in a more readable and intuitive way. The interface consists of two simple methods. Using the methods you can process form data in a generic way, without the need to worry whether only one or more values were posted under one name.

In the previous section, you learned to write following code anytime you expected a user to post more than one value under one name:. This situation is common for example when a form contains a group of multiple checkboxes with the same name:. So you write a script containing for example this code:. The problem with the code is that you should never expect that a client will provide valid input to your scripts. Calling the upper method on a list is not valid since lists do not have a method of this name and results in an AttributeError exception.

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