Decoding forms in other languages

Decoding forms in other languages Hot

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Articles Reviews CGI

Written by Bogdan V

Thursday, 12 October 2006

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Decoding forms in other languages
C/C decoding using uncgi
C/C decoding using libcgi
Tcl
Visual Basic
AppleScript

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{mos_sb_discuss:32}

Since Perl contains powerful pattern-matching operators and string manipulation functions, it is very simple to decode form information. Unfortunately, this process is not as easy when dealing with other high-level languages, as most of them lack these kinds of operators. However, there are various libraries of functions on the Internet that make the decoding process easier, as well as the uncgi program.

C Shell (csh)

It is difficult to decode form information using native C shell commands. csh was not designed to perform this type of string manipulation. As a result, you have to use external programs to achieve the task. The easiest and most versatile package available for handling form queries is uncgi, which decodes the form information and stores them in environment variables that can be accessed not only by csh, but also by any other language, such as Perl, Tcl, and C/C++.

For example, if the form contains two text fields, named "user" and "age," uncgi will place the form data in the variables WWW_user and WWW_age, respectively. Here is a simple form and a csh CGI script to handle the information:

<HTML>
<HEAD><TITLE>Simple C Shell and uncgi Example</TITLE></HEAD>
<BODY>
<H1>Simple C Shell and uncgi Example</H1>
<HR>
<FORM ACTION="/cgi-bin/uncgi/simple.csh" METHOD="POST">
Enter name: <INPUT TYPE="text" NAME="name" SIZE=40><BR>
Age: <INPUT TYPE="text" NAME="age" SIZE=3 MAXLENGTH=3><BR>
What do you like:<BR>
<SELECT NAME="drink" MULTIPLE>
<OPTION>Coffee
<OPTION>Tea
<OPTION>Soft Drink
<OPTION>Alcohol
<OPTION>Milk
<OPTION>Water
</SELECT>
<P>
<INPUT TYPE="submit" VALUE="Submit the form">
<INPUT TYPE="reset" VALUE="Clear all fields">
</FORM>
<HR>
</BODY>
</HTML>

Notice the URL associated with the ACTION attribute! It points to the uncgi executable, with extra path information (your program name). The server executes uncgi, which then invokes your program based on the path information. Remember, your program does not necessarily have to be a csh script; it can be a program written in any language. Now, let's look at the program.

#!/usr/local/bin/csh
echo "Content-type: text/plain"
echo ""

The usual header information is printed out.

if ($?WWW_name) then
    echo "Hi $WWW_name -- Nice to meet you."
else
    echo "Don't want to tell me your name, huh?"
    echo "I know you are calling in from $REMOTE_HOST."
    echo ""
endif

uncgi takes the information in the "name" text entry field and places it in the environment variable WWW_name.

In csh, environment variables are accessed by prefixing a "$" to the name (e.g., $REMOTE_HOST). When checking for the existence of variables, however, you must use the C shell's $? construct. I use $? in the conditional to check for the existence of WWW_Name. You cannot check for the existence of data directly:

if ($WWW_name) then
....
else
....
endif

If the user did not enter any data into the "name" text entry field, uncgi will not set a corresponding environment variable. If you then try to check for data using the method shown above, the C shell will give you an error indicating the variable does not exist.

The same procedure is applied to the "age" text entry field.

if ($?WWW_age) then
    echo "You are $WWW_age years old."
else
    echo "Are you shy about your age?"
endif
echo ""
if ($?WWW_drink) then
    echo "You like: $WWW_drink" | tr '#' ''
else
    echo "I guess you don't like any fluids."
endif
exit(0)

Here is another important point to remember. Since the form contains a scrolled list with the multiple selection property, uncgi will place all the selected values in the variable, separated by the " #" symbol. The UNIX command tr converts the "#" character to the space character within the variable for viewing purposes.

C/C++

There are a few form decoding function libraries for C and C++. These include the previously mentioned uncgi library, and Enterprise Integration Technologies Corporation's (EIT) libcgi. Both of them are simple to use.

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