Open selected listbox item

Hi all,

I have the following script and would like to know where I would place code to open the item once it is selected from the listbox.
I'm planning on using the header('Location: ...;) method but have no idea where to place it in the code

I hope I made myself clear on what I need
Thanks a lot

<?php
session_start();

error_reporting(E_ALL);

// THE DESIRABLE FILE NAMES ARE KEPT IN AN ARRAY
//should be able to find 123*.xml
//$signals = Array($_SESSION['username'].'*.xml'=>'regex');
//$signals = Array($_SESSION['username'].'.*\.xml'=>'regex');
  $signals = Array( '^' . $_SESSION['username'].'.*\.xml'=>'regex');
  
// THE OPTION STATEMENTS ARE COLLECTED IN AN ARRAY
$options = Array();

// COLLECT THE FILE OBJECTS
$path = realpath(getcwd());
$objs = new RecursiveIteratorIterator(new RecursiveDirectoryIterator($path), RecursiveIteratorIterator::SELF_FIRST);

// ITERATE OVER THE OBJECTS TO FIND THE DESIRABLE FILES
foreach($objs as $path => $obj)
{
    $name = $obj->getFileName();
    // this is looking for "exact" matches.
    if (in_array($name, $signals))
    {
        $options[]
        = '<option value="'
        . $path
        . '">'
        . $name
        . '</option>'
        ;
    }
	else
	{ //echo 'Searching for '.$name.PHP_EOL;
		foreach($signals as $k=>$v)
		{
            // is you set $signals = [ '123*.xml/'=>'regex', '456*.txt'=>'regex']
            //the if clause below will get executed
			if( $v=='regex' )
			{
				if( preg_match('/'. str_replace('/','\\/',$k) .'/',$name))
				{
					$options[]
					= '<option value="'
					. str_replace($_SERVER['DOCUMENT_ROOT'],'', $path)
					. '">'
					. substr($name,strlen($_SESSION['username']),strlen($name)-4-strlen($_SESSION['username'])) //Only pass file name without ext
					. '</option>'
					;
				}
			}

            // is you set $signals = [ '123'], but you have the following files: '123.xml', 'xyz-123.txt'
            // the if clause below will get executed and will find both, because this is a "contains" filter
			elseif( stripos($name, $v)!==false )
			{
				$options[]
				= '<option value="'
				. str_replace($_SERVER['DOCUMENT_ROOT'],'', $path)
				. '">'
				. $name
				. '</option>'
				;
			}
		}
	}
}

// GENERATE THE OPTION STATEMENTS
$opts = implode(PHP_EOL, $options);

// CREATE THE HTML USING HEREDOC NOTATION
$html = <<<EOD
<p>Leave History<br>
<select name="listbox" size="1">
<option value="">Open to view</option>
$opts
</select>
</p>
EOD;

// SHOW THE HTML
echo $html;

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