1、直接利用js的execCommand，此方法移动端无效

<input type="text" id="url" readonly class="form-control" name="url" placeholder="Email to:" value="<?= $sharelink ?>">
<button onClick="url.select();document.execCommand('Copy');alert('复制成功')" class="btn btn-primary btn-block"><b>复制链接</b></a>

2、引入js插件clipboard.js

<!-- 1. Define some markup -->
<div>hello</div>
<button class="btn" data-clipboard-action="copy" data-clipboard-target="div">Copy</button>

<!-- 2. Include library -->
<script src="../dist/clipboard.min.js"></script>

<!-- 3. Instantiate clipboard -->
<script>
var clipboard = new ClipboardJS('.btn');

clipboard.on('success', function(e) {
    console.log(e);
});

clipboard.on('error', function(e) {
    console.log(e);
});
</script>