Perl 101 (part 7) - CGI Basics - GETting Your Form To Work (
Page 6 of 6 )
The CGI environment comes with a set of pre-defined variables that can assist in
the task of developing server-side scripts. Here's a list of the important
ones:
$ENV{REMOTE_ADDR} The address of the client
machine
$ENV{REMOTE_HOST} The host name of the client
machine
$ENV{REQUEST_METHOD} The method used by a form to request
data
$ENV{HTTP_USER_AGENT} The client browser
$ENV{QUERY_STRING} The query
string passed if the GET method is used
Our next few examples will give
you some idea of how these, and similar variables, can be used within your
scripts.
#! /usr/bin/perl
$ip = $ENV{REMOTE_ADDR};
$browser = $ENV{HTTP_USER_AGENT};
print "Content-Type: text/html\n\n";
print "<html><body><font face=Arial>Your IP address is $ip and your browser
is $browser</font></body></html>";
And now, when you browse to this page, you'll see some
information on your IP address and browser version.
Our next example
demonstrates how a Perl/CGI script can be used to process data submitted via a
form. Here's the form...
<html>
<head>
<basefont face=Arial>
</head>
<body>
<form action=http://localhost/readform.cgi method=GET>
Enter your first name: <input type=text length=20 name=name><br>
<input type=submit value=Submit>
</form>
</body>
</html>
...and here's the CGI script that receives and processes the
data.
#!/usr/bin/perl
# readform.cgi
# reads form data and generates a page
# for GET data
if ($ENV{'REQUEST_METHOD'} eq "GET")
{
$yourname=$ENV{'QUERY_STRING'};
}
# for POST data
else
{
$yourname = <STDIN>;
}
# Remove spaces if any
$yourname =~ s/\+/ /g;
# split form data and store in hash
%details = split (/=/, $yourname);
# generate page
print "Content-Type: text/html\n\n";
print "<html><body>";
while (($name, $value) = each %details)
{
print "Thank you for your submission, $value!\n";
}
print "</body></html>";
The script above will accept data from the HTML form and
store it in a variable called $yourname. The manner in which data is submitted
by the form(GET or POST) decides the manner in which it is assigned to the
variable; the QUERY_STRING environment variable is used to make this
decision.
If the text entered into the form contains spaces, the spaces
are replaced with + characters when the form is submitted - this needs to be
reversed via a regex. For example, if you enter the name "Luke Skywalker" into
the form, the URL string will look like
this:
http://localhost/cgi-bin/readform.cgi?name=Luke+Skywalker
Next,
the name-value pairs are split apart on the basis of the = sign, and are
assigned to their respective places in the hash %details. This hash is then used
to print the name in the result page, which is also generated by the same
script.
Thus, the CGI environment can be used to accept data from one Web
page, process it or transfer it to another, and generate a new page containing
dynamically-generated output. This is the basis of using CGI to create dynamic
Web sites.
In the next issue of Perl 101, we'll delve deeper into CGI,
with a look at some simple CGI programs that can be used to track hits on your
Web site, or store visitor comments. Don't miss it!
