function copyToClipboard(elementId) {

var aux = document.createElement("input");

aux.setAttribute("value", document.getElementById(elementId).innerHTML);

document.body.appendChild(aux);

aux.select();

document.execCommand("copy");

document.body.removeChild(aux);

alert("복사되었습니다.");

}

<p class="hidden" id="copy_url"><?php echo "https://$_SERVER[HTTP_HOST]$_SERVER[REQUEST_URI]"; ?></p>

<button type="button" onclick="copyToClipboard('copy_url')" class="btn btn-default"><i class="fti link_copy"></i><span class="ft11 text-black ml-5">링크 복사하기</span></button>