Editing Contribute: Plugins/ExportPluginsList (section)

== Filehandles ==
The command line export tool provides the output list method with a filehandle for output in the opts hash, while the [http://en.wikipedia.org/wiki/Common_Gateway_Interface CGI] export uses a value returned from the method. You must deal with the filehandle or you will get no output from the command line tool. In most cases this won't matter, but it is good practice to deal with it.

The best way to handle output is to check if a filehandle has been provided every time something needs to be output. If a filehandle is provided we print to it, otherwise we save the output for later. At the end of the method we either return undef if a filehandle was provided or we return the saved output otherwise.

<pre>
sub output_list
{
        my ($plugin, %opts) = @_;

        my $r = [];

        my $header = "ID\tTitle\n\n";
        if (defined $opts{fh})
        {
                print {$opts{fh}} $header;
        }
        else
        {
                push @{$r}, $header;
        }

        foreach my $dataobj ($opts{list}->get_records)
        {
                my $part = $plugin->output_dataobj($dataobj, %opts);
                if (defined $opts{fh})
                {
                        print {$opts{fh}} $part;
                }
                else
                {
                        push @{$r}, $part;
                }
        }

        if (defined $opts{fh})
        {
                return undef;
        }
        return join('', @{$r});
}
</pre>