Use CGI's html generation methods.

# Assuming $q is from CGI->new
my $url = $q->My::CGI::hypothetical_param( search => 'value' )->self_u
+rl;

sub My::CGI::hypothetical_param {
    my $current_q = shift;
    my $q = CGI->new( $current_q );

    my $params = { @_ };
    while ( my ( $param, $value ) = each %$params ) {
        if ( not defined $value ) {
            $q->delete ( $param );
        }
        else {
            $q->param( $value );
        }
    }

    $q;
}
[download]