add_google_analytics_tag.sh

TARGET='<script>(function (w, d, s, l, i) { w[l] = w[l] || []; w[l].push({ "gtm.start": new Date().getTime(), event: "gtm.js" }); var f = d.getElementsByTagName(s)[0], j = d.createElement(s), dl = l != "dataLayer" ? "&l=" + l : ""; j.async = true; j.src = "https:\/\/www.googletagmanager.com\/gtm.js?id=" + i + dl; f.parentNode.insertBefore(j, f); })(window, document, "script", "dataLayer", "GTM-W6T5HDN");<\/script> <noscript><iframe src="https:\/\/www.googletagmanager.com\/ns.html?id=GTM-W6T5HDN" height="0" width="0" style="display:none;visibility:hidden"><\/iframe><\/noscript><\/head>'
SOURCE='<\/head>'

sed -i.bak "s/$SOURCE/$TARGET/g" public/index.html
rm public/index.html.bak