WordPress: Simple, configurable script to export post data to a CSV file

wordpress_export-post-data.php

<?php
/**
 * Export WordPress post data to CSV
 * Based on <http://stackoverflow.com/a/3474698> and <http://ran.ge/2009/10/27/howto-create-stream-csv-php/>
 */

/**
 *********************************************************************
 * Configuration
 *********************************************************************
 */

/**
 * Path to WordPress installation root
 * Default path './'
 */
// define( 'PATH_TO_WORDPRESS', './' ); # Default WordPress install location
define( 'PATH_TO_WORDPRESS', './wordpress/' ); # Default WordPress sub-directory install location


/**
 * Export fields: array of strings representing $post properties to output to CSV.
 */
$export_fields = array(
	'post_title',
	'post_date'
);


/**
 * Export query parameters for WP_Query
 * @link http://codex.wordpress.org/Function_Reference/WP_Query WP_Query parameter reference
 */
$export_query = array(
	'posts_per_page' => -1,
	'post_status' => 'publish',
	'post_type' => 'any',
);


/**
 *********************************************************************
 * Data export
 *********************************************************************
 */

// Require WordPress environment
require PATH_TO_WORDPRESS . 'wp-load.php';

// Posts query
$posts = new WP_Query( $export_query );
$posts = $posts->posts;

// Output file stream
$output_filename = 'export_' . strftime( '%Y-%m-%d' )  . '.csv';
$output_handle = @fopen( 'php://output', 'w' );

header( 'Cache-Control: must-revalidate, post-check=0, pre-check=0' );
header( 'Content-Description: File Transfer' );
header( 'Content-type: text/csv' );
header( 'Content-Disposition: attachment; filename=' . $output_filename );
header( 'Expires: 0' );
header( 'Pragma: public' );

// Output data to file
foreach ( $posts as $post ) {

	// Get post permalink
	switch ( $post->post_type ) {

		case 'revision':
		case 'nav_menu_item':
			break;
		case 'page':
			$permalink = get_page_link( $post->ID );
			break;
		case 'post':
			$permalink = get_permalink( $post->ID );
			break;
		case 'attachment':
			$permalink = get_attachment_link( $post->ID );
			break;
		default:
			$permalink = get_post_permalink( $post->ID );
			break;

	}

	// Build export array
	$post_export = array( $permalink );
	foreach ( $export_fields as $export_field ) {
		$post_export[] = $post->$export_field;
	}

	// Add row to file
	fputcsv( $output_handle, $post_export );

}

// Close output file stream
fclose( $output_handle );

// We're done!
exit;
?>

Hi, I'm trying to do the same thing but calling this function from a button that is posted inside a plugin. Do you know if is it possible to export this data from a plugin inside the admin panel?
Right now I'm able to show the data of the table in the plugin but is doesn't export anything (like I show you in the picture). As I said I'm using the same code as you in a function that is written in a plugin that shows the data in a table and has a button to export it.