Introduction
This tutorial provides a handy resource for everything you need to know to make and keep cgi scripts running,using PERL, the World's friendliest language.Forms in HTML
Cgi Scripting is one that is widely used in all the platforms available under the sun. The scope of this tutorial limits itself to taste the flavour of Unix and Windows 95/NT alone.
To begin with, I shall discuss ideas that are common to both Unix and the Windows platforms and later point out the areas in which they differ under the respective
sections.
The introduction is divided into the following sections:
Forms in HTML, contain fields whose values are
to be
typed in by the user and submitted to the server side to
be manipulated by the Cgi Scripts.
Most commonly cited usage of these forms is to collect
User feedback and comments about a particular site or a
product advertised.
The structure of the form tag is as follows:
< form Name="first" Method="GET" action="/cgi-bin/xyz.cgi">
< /form>
The 'Name' attribute of the form is optional and is used
to differentiate the different forms that may be placed
within a single HTML page.
The 'Method' attribute can contain a value of 'GET'
or
'POST', the default one being 'GET'. 'GET' is rarely used
in cases where the form contents to be submitted
is
too small in size. i.e , a Name field and a age field.
In
our discussion we shall limit ourselves to the
'POST'
method which is the most commonly used one.
This
method converts the fields
(form elements) into
'name=value' pairs separated by an '&'
and transfers
them.
The value of the 'Action' attribute specifies which
cgi
script is to be called upon the submission of this form.
The contents inside the < form> and < /form> could
be
any valid HTML element. Generally the following are used
to represent text fields, password fields, buttons, etc.
Text Input:
< input type="text" name='anyname' value='ifany'>
which shows up on the browser like this
Password Input :
< input type="password" name='pass' value='ifrequired'>
which shows up like this
Submit :
< input type="Submit" value='Submit Form'>
which produces an output like this and submits
the form to the server
Reset :
< input type="reset" Value="Clear">
which produces an output like this and resets / clears
the form fields
These are the basics you need to know to handle 'forms'
in Web pages.
The
work of the CGI Scripts start once the form elements
reach the server. The invoked cgi scripts receive the form
elements as environment variables.
The form elements are rendered
in the form of
'elementname=elementvalue' which are to
be split
to make the data received,usable. You can yourself write
lines of Perl code to achieve the task ( Finding out which
method of submission has been used, either
'GET' or
'POST'. If 'GET' is used
then reading the submitted
elements by using $ENV{'QUERY_STRING'}
or else if
'POST' is used reading STDIN- The Standard
Input to
the extent of $ENV{'CONTENT-LENGTH'}, splitting
all
the 'name=value' pairs demarcated by '&' Symbol,
and
further splitting the 'names' separately from the 'values'
delimited by the '=' symbol.... Whew!) or might
as well
settle for an easier and effective solution, 'the
cgi-lib'
module.
'cgi-lib.pl'
This module written
by Mr. Steven.E.Brenner is
downloadable from
http://cgi-lib.stanford.edu/cgi-lib/ and
is a handy tool that comes to the rescue
of the Cgi
programmers. The subroutine 'ReadParse' receives
the
submitted form elements and does
all the necessary
manipulations and finally renders the form elements
as
an associative array named 'IN'.
Let us
now see an example, of how the tasks about which
we have discussed until now gets accomplished.
Client Side
Customer Detail's Collection Form
This is how the HTML form looks at the client side,
the code for which is as follows:
< html>
< head>
< title> Customer details collection form< /title>
< /head>
< body>
< FORM Name="FirstTrial" METHOD="POST"
Action= "cgi-bin/demo.cgi">
Enter the Name : < input type="text" name="name">
Enter your age : < input type="text" name="age">
< input type="Submit">
< /FORM>
< /body>
< /html>
Server Side
At the server side this data reaches in the following
format
" name=The+name+you+typed&age=31 "
Notice how the spaces are transformed into '+' Symbols.
This data is meaningfully converted using the following
Perl Code with the help of the 'cgi-lib' module , we
discussed earlier.
1. require "cgi-lib.pl";
2. &ReadParse;
3. $nameoftheemployee=$in{'name'};
4. $age=$in{'age'};
Line 1 : Includes the "cgi-lib.pl" module into the perl
code.
Line 2 : Calls the subroutine ' ReadParse '.
Line 3 : The value of the variable 'Name' is stored in the
scalar variable '$nameoftheemployee'.
Line 4 : The value of the variable 'Age' is stored in the
scalar variable '$age'.
This
brings us to the end of the
introductory section.
Let us now proceed to find out how
the data submitted
gets stored and retrieved in
a database under the
Windows platform.
