<input type="text" name="path1" size="25" maxlength="40" value="guping/ckxx______.txt">
<button onclick="with(path1){value=value.replace('______','nowdate')}">test</button>
<button onclick="with(path1){value=value.replace('______','nowdate')}">test</button>
<body onload="document.all('pathl').value=nowdate"></body>