Move posts from cat1 to cat2

gistfile1.php

<?php

ini_set("display_errors", 1);
ini_set("error_reporting", E_ALL);
set_time_limit( 0 )

require 'wp-load.php'; // in case you place it in a seperate file

$args = array(  
	'category_name' => 'cat1',
	'posts_per_page' => -1,
	'meta_query' => array(
      		array(
			'key' => 'has_moved',
			'compare' => 'NOT EXISTS'
      		)
    	)
);

$posts = new WP_Query( $args );

echo "Still ".$posts->found_posts." posts to update";

if ( $posts->have_posts() ) : 
	while ($posts->have_posts()) : 
		$posts->the_post();

		wp_set_object_terms(get_the_ID(), 'cat2', 'category');
		update_post_meta( get_the_ID(), "has_moved", mktime() );
    
	endwhile; 
endif;

echo "Done!";

?>