CODEWITHSUNDEEP
perlcgi
serv-inc
serv-inc

Reputation: 38237

Check for the existence of empty parameters in CGI.pm

To check if a request parameter has a value (http://example.com?my_param=value) you can use 

query->param('my_param')

This seems to be flaky if the no_value form is used: http://example.com?my_param .

Is there a way to check simply the existence of parameters in CGI.pm ?

Upvotes: 1

Views: 561

Answers (2)

Georg Mavridis
Georg Mavridis

Reputation: 2341

You can check whether the parameter is present with defined. the following code 

#!/usr/bin/env perl
use strict;
use warnings;
use CGI;
my $cgi = CGI->new();
print $cgi->header;

my $defined = defined $cgi->param('tt');
my $val = $cgi->param('tt');
print <<END;
<!doctype html>
<html> HTML Goes Here 
<h1>tt: "$defined" "$val"</h1>
</html>
END

Will generate the output:

<!doctype html>
<html> HTML Goes Here 
<h1>tt: "1" ""</h1>
</html>

when the URI is http:///cgi-bin/t.pl?someother=something&tt

Unfortunately this doesn't work when it is the only parameter.

So to be sure, you have to test:

my $defined = defined $cgi->param('tt') || $ENV{QUERY_STRING} eq 'tt';

Upvotes: 3

simbabque
simbabque

Reputation: 54333

This seems to depend on the browser implementation. According to this Perlmonks thread from 2001, empty parameters might not be returned. But if they are, the key will be there, but contain an empty string q{}. If the argument wasn't present, it will be undef, so you can check with defined.

Upvotes: 2

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