To add button you may use either jQuery libraries or simple Javascript script as shown below:
HTML link or button:
<a href="#" onClick="goclear()" id="button">click event</a>
Javascript:
<script type="text/javascript">
var btn = document.getElementById('button');
function goclear() {
alert("Handler called. Page will redirect to clear.php");
document.location.href = "clear.php";
};
</script>
Use PHP to clear a file content. For instance you can use the fseek($fp, 0); or ftruncate ( resource $file , int $size ) as below:
<?php
//open file to write
$fp = fopen("/tmp/file.txt", "r+");
// clear content to 0 bits
ftruncate($fp, 0);
//close file
fclose($fp);
?>
Redirect PHP - you can use header ( string $string [, bool $replace = true [, int $http_response_code ]] )
<?php
header('Location: getbacktoindex.html');
?>
I hope it's help.