bootstrap怎么给input加图标

<div class="input-group">
 <div class="input-icon-group">
 <input type="text" class="form-control fc-clear" /> 
 <span id="scan" data-role="md" class="md md-center-focus-weak fa-lg input-icon input-icon-md" style="display: inline;"> 
 </span>
 </div>
 <span class="input-group-btn">
 <button class="btn btn-primary" type="button">
 批号 </button>
 </span>
</div>