Flat file export, first pass...

flatfile.php

<?php
/*
Plugin Name: Flat File Database
Description: Exports WP data into a series of flat files. Hence the name.
Author: goldenapples
Author URI: http://goldenapplesdesign.com
Version: 0.1
License: GPLv2
*/

// add the admin options page
add_action('admin_menu', 'flat_file_controls');

function flat_file_controls() {
	add_management_page( 'Flat File Export', 'Export all posts as flat files', 'edit_theme_options', 'ffe', 'flat_file_controls_page');
}


function flat_file_controls_page() {
	if ( flat_file_export() ) return;
?>
<div>
<h2>Export site to flat files</h2>
<form action="" method="post">
<?php wp_nonce_field('flat-file-export'); ?>
<input name="save" type="submit" value="Backup entire database to flat files" />
</form></div>
<?php
}

/**
 * function flat_file_export
 *
 * Checks to get valid filesystem credentials (this section is all copypasta from Otto's post
 * at http://ottopress.com/2011/tutorial-using-the-wp_filesystem/); then if successful, begins
 * to go about walking through posts and saving them to text files.
 *
 * @return void
 * @author goldenapples
 **/
function flat_file_export(  ) {
	if (empty($_POST)) return false;

	check_admin_referer('flat-file-export');

	$form_fields = array( 'save' );

	$url = wp_nonce_url('tools.php?page=ffe','flat-file-export');
	if ( false === ( $creds = request_filesystem_credentials($url, '', false, false, $form_fields) ) ) {
		// if we get here, then we don't have credentials yet,
		// but have just produced a form for the user to fill in,
		// so stop processing for now
		return true; // stop the normal page form from displaying
	}

	// now we have some credentials, try to get the wp_filesystem running
	if ( ! WP_Filesystem($creds) ) {
		// our credentials were no good, ask the user for them again
		request_filesystem_credentials($url, '', true, false, $form_fields);
		return true;
	}

	global $wp_filesystem;
	$upload_dir = wp_upload_dir();

	// $e_root; the export root, so to speak.
	global $e_root;
	$e_root = $upload_dir['basedir'].'/export' ;

	// Make sure root folder exists
	if ( !$wp_filesystem->exists( $e_root ) )
		$wp_filesystem->mkdir( $e_root );

	// Also a folder for content, and one for taxonomies
	if ( !$wp_filesystem->exists( $e_root . '/content' ) )
		$wp_filesystem->mkdir( $e_root . '/content' );
	if ( !$wp_filesystem->exists( $e_root . '/taxonomy' ) )
		$wp_filesystem->mkdir( $e_root . '/taxonomy' );

	foreach ( get_post_types( null, 'names', 'public=true' ) as $post_type ) {

		$local_dir = post_type_dir( $post_type );

		$taxonomies = get_object_taxonomies( $post_type );

		// Make folders now, for each of the taxonomies attached to this post type
		foreach ( $taxonomies as $tax )
			if ( !$wp_filesystem->exists( $e_root . '/taxonomy/' . $tax ) )
				$wp_filesystem->mkdir(  $e_root . '/taxonomy/' . $tax );

		$posts_in_type =  get_posts(
			array(
				'post_type' => $post_type,
				'post_status' => 'publish',
				'nopaging' => true
			)
		);

		foreach ( $posts_in_type as $post ) {
			setup_postdata( $post );

			$object_terms = array();
			$post_tax_output = '';

			foreach ( $taxonomies as $tax ) {
				$object_terms[$tax] = wp_get_object_terms( $post->ID, $tax, array( 'fields' => 'names' ) );
				$post_tax_output .= $tax . ': ' . implode( ',', $object_terms[$tax] ) . "\r\n";
			}

			// This is the template the post content will be stored in
			$template = <<<FORMAT
Title: {$post->post_title}
Author: {$post->post_author}
Posted:  {$post->post_date}
Slug: {$post->post_name}
{$post_tax_output}

==============================

{$post->post_content}

==============================

FORMAT;

			/*
			 * Handle all public meta values attached to a post.
			 *
			 * Meta values will be output in the format:
			 *
			 * [Meta:{$meta_key}]
			 * {$meta_value}
			 *
			 * ==============================
			 *
			 * (30 or more equals signs are used as a delimiter here, as elsewhere)
			 */
			foreach ( get_post_custom( $post->ID ) as $key => $val ) {
				if ( strpos( $key, '_' ) === 0 )
					continue;
				if ( is_array( $val ) && count( $val ) === 1 )
					$val = $val[0];
				else $val = print_r( $val, true );
				$template .= "[Meta:$key]" . "\r\n" . $val
					. "\r\n==============================\r\n\r\n";
			}

			$post_loc = $local_dir . $post->post_name . '.txt';
			$wp_filesystem->put_contents( $post_loc, $template, FS_CHMOD_FILE );

			// Now, go back through and create symlinks for this post in all the taxonomy folders
			foreach ( $taxonomies as $tax )
				foreach ( $object_terms[$tax] as $term ) {
					if ( !$wp_filesystem->exists( $e_root . '/taxonomy/'. $tax . '/' . $term ) )
						$wp_filesystem->mkdir( $e_root . '/taxonomy/'. $tax . '/' . $term );
					symlink( $post_loc, "$e_root/taxonomy/$tax/$term/{$post->post_name}.txt" );
				}

		}
	}

}

/**
 * Return the path to a post type directory
 *
 * @return str
 * @author goldenapples
 **/
function post_type_dir( $post_type ) {
	global $e_root, $wp_filesystem;
	$dir = trailingslashit( $e_root . '/content/' . $post_type );
	if ( !$wp_filesystem->exists( $dir ) )
		$wp_filesystem->mkdir( $dir );
	return $dir;
}

/**
 * undocumented function
 *
 * @return void
 * @author goldenapples
 **/
function flat_file_headers(  ) {
	return array( 'Title', 'Author', 'Posted', 'Slug', 'Catgories', 'Tags' );
}

add_filter( 'extra_flatfile_headers', 'flat_file_headers' );