Regular Expression

Hello guys i would like to replace the string in this line -> $batch_file1 = 'service_pack.bat'; It is located on another php file. I have tried doing it for an hour but to no avail, can someone guide me? Thanks!

<?php

$file = 'C:\xampp\htdocs\new\editpolicy.php';
$batch_contents = file_get_contents($file);

if(isset($_POST['argument']) && $_POST['submit'] == "Save")
{

$newArgument = $_POST['argument'];

preg_replace('~$\batch_file1 = "([a-z0-9_ -]+)"~i', '$\batch file1 = "'.$newArgument.'"' ,$batch_contents);
}file_put_contents($file, $batch_contents);

?>


<b>Deploy Service Pack Policy</b>
<p>
<form action="deploy.php" method="post">
Select audit file to deploy: <input type="text" name="argument"<br>
<input type="submit" name="submit" value="Save"> &nbsp;<p>
</form>
</p>

 

<?php
$file = 'C:\xampp\htdocs\new\editpolicy.php';
$batch_contents = file_get_contents($file); 
if (isset($_POST['argument']) && $_POST['submit'] == "Save") {
$batch_contents = preg_replace('~\$batch_file1\s*=\s*"(.+?)"~i', '$batch_file1 = "'.$newArgument.'"', $batch_contents);
file_put_contents($file, $batch_contents);
}
?>

PHP:

 

thanks bro!