songlink-share.user.js

// ==UserScript==
// @name         Songlink
// @match        https://play.google.com/music/listen?*
// @version      1.0
// @downloadURL  https://gist.github.com/okj579/c890d574ac026151f9ebdde9b298ba87/raw/songlink-share.user.js
// ==/UserScript==

(function() {
    'use strict';
    document.addEventListener('iron-overlay-opened', function(e) {
        if (!e.target.classList.contains('get-link')) return;
        var link = document.querySelector('.link', e.target);
        link.value = link.value.replace(/.*\/\/play.google.com\/music\/m\/(.*)\?.*/, 'https://songlink.io/g/$1');
        document.querySelector('input.paper-input', link).select();
    });
})();