PHP auto refresh - php

Question

I am having some trouble coding a PHP script to update only when the value in a .txt file changes. What happens is that a VB form can change the value in the .txt file and the PHP script displays an image based on the value in the .txt file. Currently the script will show the updated files if I manually hit refresh on the browser, but I would like to eliminate that. I have tried using the meta refresh tag but because I am rendering images the page is very "jolty" when it refreshes every 2 or so seconds and makes viewing the page unbearable. What I have tried to do is create a loop between the $string and $string2 variables so that when they are not equal it redirects the page to a page that redirects back to this page and does a "back-door" refresh. $string is what is the direct value in the .txt file and it defined in the loop whereas $string2 is defined outside of the loop. I would the loop to see the difference between them once a different value is inputted to the .txt file.
Thank you all in advance.
<?php
{
$file=fopen("counter.txt","r");
$string=fgetc($file);
fclose($file);
}
$string2 = $string;
if ($string == '1') {
$files = glob('tg.jpg');
foreach($files as $file) {
echo '<img src="' . $file . '" />';
}}
elseif ($string == '2') {
$files = glob('tr.jpg');
foreach($files as $file) {
echo '<img src="' . $file . '" />';
}}
elseif ($string == '3') {
$files = glob('wua.jpg');
foreach($files as $file) {
echo '<img src="' . $file . '" />';
}}
elseif ($string == '4') {
$files = glob('wur.jpg');
foreach($files as $file) {
echo '<img src="' . $file . '" />';
}}
elseif ($string == '5') {
$files = glob('stop.jpg');
foreach($files as $file) {
echo '<img src="' . $file . '" />';
}}
elseif ($string == '6') {
$files = glob('base.jpg');
foreach($files as $file) {
echo '<img src="' . $file . '" />';
}}
while ($string == $string2) {
$file=fopen("counter.txt","r");
$string=fgetc($file);
echo $string;
fclose($file);
}
header('Location: redirect.php');
exit;
?>

Answer 1

PHP only runs in runtime, so there is no chance you can do what you just described.
Your best bet is to create a very small PHP script that does the check and have an AJAX script on the frontend check every second and update the image if PHP returns that it has been updated.

Answer 2

You are trying to use a server-side script to perform something on the client side.
Have your client page include a small Javascript snippet which posts back to your server to a script which can perform the check. Then, if your script indicates that a change had occured, refresh the page using Javascript.
That way, the page will only refresh when needed, and you can easily separate your client and server code.