When we built the form processor, we
saw that we could use one CGI script to reference another by
outputting an HTML form. This is pretty powerful since in
theory, you could have a web site with no HTML files, but only
CGI scripts.
However, in many CGI applications, it is
more common for a CGI script to contain routines to display AND
process a FORM. This is called a self-referential script because
it outputs a form whose FORM tag points back to itself.
In order to determine what it should do
(output a form or process a form) the script needs some extra
logic.
The most common way for a CGI script to
decide what it should do is to look at the state of the submit
button.
The idea is this. If no submit button
has been pressed, we can assum that the script is being executed
for the first time. Thus, we should output the FORM. If a submit
button has a value, that means that the user has already received
the form and is now submitting it for processing.
Consider the following self-referential
script called self-refer.cgi:
#!/usr/local/bin/perl
require "cgi-lib.pl";
&ReadParse(*form_data);
print "Content-type: text/html\n\n";
if ($form_data{'submit'} eq "")
{
print qq!
<HTML>
<HEAD>
<TITLE>Testing Form Input</TITLE>
</HEAD>
<BODY>
<FORM METHOD = "POST" ACTION = "self-refer.cgi">
<CENTER>
<TABLE BORDER = "1">
<TR>
<TH>First Name</TH>
<TD><INPUT TYPE = "text"
NAME = "f_name"></TD>
</TR>
<TR>
<TH>Last Name</TH>
<TD><INPUT TYPE = "text"
NAME = "l_name"></TD>
</TR>
<TR>
<TH>Email</TH>
<TD><INPUT TYPE = "text"
NAME = "email"></TD>
</TR>
</TABLE>
<P>
<INPUT TYPE = "SUBMIT" NAME = "submit">
</CENTER>
</FORM>
</BODY>
</HTML>!;
exit;
}
else
{
print qq!
<HTML>
<HEAD>
<TITLE>Testing Form Input</TITLE>
</HEAD>
<BODY>
<TABLE>!;
foreach $key (keys(%form_data))
{
print qq!
<TR>
<TD>$key</TD>
<TD>$form_data{$key}</TD>
</TR>!;
}
print qq!
</TABLE>
</BODY>
</HTML>!;
}
