functions.php

<?php 

/* Do Not copy open php tag */
/**
* @author    Hunk Riyaz
* @link      http://extracatchy.net
*/

function add_copyright_text() {
	if (is_single()) { ?>

<script type='text/javascript'>
function addLink() {
	if (
window.getSelection().containsNode(
document.getElementsByClassName('entry-content')[0], true)) {
    var body_element = document.getElementsByTagName('body')[0];
    var selection;
    selection = window.getSelection();
	var oldselection = selection
    var pagelink = "<br /><br /> Read more at ExtraCatchy: <?php the_title(); ?> <a href='<?php echo wp_get_shortlink(get_the_ID()); ?>'><?php echo wp_get_shortlink(get_the_ID()); ?></a>"; //Change this if you like
    var copy_text = selection + pagelink;
    var new_div = document.createElement('div');
	new_div.style.left='-99999px';
	new_div.style.position='absolute';

    body_element.appendChild(new_div );
    new_div.innerHTML = copy_text ;
    selection.selectAllChildren(new_div );
    window.setTimeout(function() {
        body_element.removeChild(new_div );
    },0);
}
}


document.oncopy = addLink;
</script>

<?php
}
}

add_action( 'wp_head', 'add_copyright_text');