Move metadata from one Wordpress site to another (quick and dirty)

functions.php

<?php

// Add this to the functions.php file of the SENDING site
function fh_export_page_metadata(){
    $post = get_post();

    // change this to target site URL
    $target_site = 'http://www.example-site.com';

    // add 'run' to URL query string to run this
    if ( !empty($_REQUEST['run']) ){

        // get all pages
        $args = array(
    		'posts_per_page'   => -1,
            'order'            => 'ASC',
    		'post_type'        => 'page',
    		'post_status'      => 'any'
    	);
    	$all_posts = get_posts($args);

        // init output
        $out = array();

        // loop pages
        foreach ($all_posts as $this_post){

            // get all page meta you want to transfer
            $page_meta = get_post_meta($this_post->ID, '_custom_page_meta', true);
            $media_meta = get_post_meta($this_post->ID, '_custom_media_meta', true);

            // add post ID and two meta values to output
            $out[] = array(
                'page_id' => $this_post->ID,
                'page_meta' => $page_meta,
                'media_meta' => $media_meta
            );

        }

        // encode as JSON
        $encoded = json_encode($out);

        // send POST request with all metadata and associated page IDs
        $response = wp_remote_post( $target_site . '/wp-admin/admin-ajax.php?action=fh_meta_import', array(
        	'method' => 'POST',
        	'timeout' => 60,
        	'redirection' => 5,
        	'httpversion' => '1.0',
        	'blocking' => true,
        	'headers' => array(),
        	'body' => $encoded,
        	'cookies' => array()
            )
        );

        // dump response and exit when done
        var_dump($response); exit;

    }

}
add_action('init', 'fh_export_page_metadata');


// Add this to the functions.php file of the RECEIVING site
function fh_receive_imported_meta(){

    // get JSON data from incoming request
    $data = json_decode(file_get_contents('php://input'), true);

    // start counter
    $count = 0;

    // loop all incoming pages
    foreach ( $data as $single_post ){

        // update meta by ID
        $page_meta = update_post_meta($single_post['page_id'], '_custom_page_meta', $single_post['page_meta']);
        $media_meta = update_post_meta($single_post['page_id'], '_custom_media_meta', $single_post['media_meta']);

        // incrememnt counter
        $count++;

    }

    // output results and exit
    echo 'success! Updated posts: ';
    echo $count;
    exit;

}
add_action( 'wp_ajax_fh_meta_import', 'fh_receive_imported_meta' );
add_action( 'wp_ajax_nopriv_fh_meta_import', 'fh_receive_imported_meta' );