Here is the code, I hope it works:

     <meta name="viewport" content="width=device-width, initial-scale=1.0"> 
<?php
// Simple PHP Upload Script:  http://coursesweb.net/php-mysql/

$uploadpath = 'upload/';      // directory to store the uploaded files
$max_size = 5000;          // maximum file size, in KiloBytes
$alwidth = 900;            // maximum allowed width, in pixels
$alheight = 800;           // maximum allowed height, in pixels
$allowtype = array('png', 'mp3');        // allowed extensions

if(isset($_FILES['fileup']) && strlen($_FILES['fileup']['name']) > 1) {
  $uploadpath = $uploadpath . basename( $_FILES['fileup']['name']);       // gets the file name
  $sepext = explode('.', strtolower($_FILES['fileup']['name']));
  $type = end($sepext);       // gets extension
  list($width, $height) = getimagesize($_FILES['fileup']['tmp_name']);     // gets image width and height
  $err = '';         // to store the errors

  // Checks if the file has allowed type, size, width and height (for images)
  if(!in_array($type, $allowtype)) $err .= 'The file: <b>'. $_FILES['fileup']['name']. '</b> not has the allowed extension type.';
  if($_FILES['fileup']['size'] > $max_size*1000) $err .= '<br/>Maximum file size must be: '. $max_size. ' KB.';
  if(isset($width) && isset($height) && ($width >= $alwidth || $height >= $alheight)) $err .= '<br/>The maximum Width x Height must be: '. $alwidth. ' x '. $alheight;

  // If no errors, upload the image, else, output the errors
  if($err == '') {
    if(move_uploaded_file($_FILES['fileup']['tmp_name'], $uploadpath)) { 
      echo 'File: <b>'. basename( $_FILES['fileup']['name']). '</b> successfully uploaded:';
      echo '<br/>File type: <b>'. $_FILES['fileup']['type'] .'</b>';
      echo '<br />Size: <b>'. number_format($_FILES['fileup']['size']/1024, 3, '.', '') .'</b> KB';
      if(isset($width) && isset($height)) echo '<br/>Image Width x Height: '. $width. ' x '. $height;
      //echo '<br/><br/>File address: <b>http://'.$_SERVER['HTTP_HOST'].rtrim(dirname($_SERVER['REQUEST_URI']), '\\/').'/'.$uploadpath.'</b>';
        echo '<br><br><br> NOW COOPY THIS LINK';
      
    }
    else echo '<b>Unable to upload the file.</b>';
  }
  else echo $err;
}
?>
<div style="margin:1em auto; width:333px; text-align:center;">
 <form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="POST" enctype="multipart/form-data"> 

           
 <input type="text" value=<?php echo 'http://'.$_SERVER['HTTP_HOST'].rtrim(dirname($_SERVER['REQUEST_URI']), '\\/').'/'.$uploadpath.'';?> id="myInput">

<?php 
if(isset($err) && $err == '')
{
?>
 <button onclick="myFunction()">Copy text</button>
<?php 
}
?>
    
 <script>
function myFunction() {
 var copyText = document.getElementById("myInput");
  copyText.select();
    copyText.setSelectionRange(0, 99999)
     document.execCommand("copy");
    alert("Copied the text: " + copyText.value);
   }
  </script> 

<br><br>




 <form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="POST" enctype="multipart/form-data"> 
  Files uploader for DANMAKU CREATE<br>Allowed files: .png(max 1mb) .mp3(max 5 mb)<br><br> <input type="file" name="fileup" /><br/><br>
  <input type="submit" name='submit' value="Upload" /> 
 </form>
</div>

this is what I changed on your button. The error variable must be set(because that means it passed the post request) and must be empty to check if there was an error or not:

<?php 
if(isset($err) && $err == '')
{
?>
 <button onclick="myFunction()">Copy text</button>
<?php 
}
?>

Ok so i found this file uploader, its something exactli i need to my game – a image and music uploader.

Well orginally there was just link you can copy and select so i made little textbox with copy button you can see at bottom but its visible even before file is uploaded. help me dooing this to appear only after file upload. I dont know much about website coding, i cant handle it without “if” 😀

 <meta name="viewport" content="width=device-width, initial-scale=1.0"> 
<?php
// Simple PHP Upload Script:  http://coursesweb.net/php-mysql/

$uploadpath = 'upload/';      // directory to store the uploaded files
$max_size = 5000;          // maximum file size, in KiloBytes
$alwidth = 900;            // maximum allowed width, in pixels
$alheight = 800;           // maximum allowed height, in pixels
$allowtype = array('png', 'mp3');        // allowed extensions

if(isset($_FILES['fileup']) && strlen($_FILES['fileup']['name']) > 1) {
  $uploadpath = $uploadpath . basename( $_FILES['fileup']['name']);       // gets the file name
  $sepext = explode('.', strtolower($_FILES['fileup']['name']));
  $type = end($sepext);       // gets extension
  list($width, $height) = getimagesize($_FILES['fileup']['tmp_name']);     // gets image width and height
  $err = '';         // to store the errors

  // Checks if the file has allowed type, size, width and height (for images)
  if(!in_array($type, $allowtype)) $err .= 'The file: <b>'. $_FILES['fileup']['name']. '</b> not has the allowed extension type.';
  if($_FILES['fileup']['size'] > $max_size*1000) $err .= '<br/>Maximum file size must be: '. $max_size. ' KB.';
  if(isset($width) && isset($height) && ($width >= $alwidth || $height >= $alheight)) $err .= '<br/>The maximum Width x Height must be: '. $alwidth. ' x '. $alheight;

  // If no errors, upload the image, else, output the errors
  if($err == '') {
    if(move_uploaded_file($_FILES['fileup']['tmp_name'], $uploadpath)) { 
      echo 'File: <b>'. basename( $_FILES['fileup']['name']). '</b> successfully uploaded:';
      echo '<br/>File type: <b>'. $_FILES['fileup']['type'] .'</b>';
      echo '<br />Size: <b>'. number_format($_FILES['fileup']['size']/1024, 3, '.', '') .'</b> KB';
      if(isset($width) && isset($height)) echo '<br/>Image Width x Height: '. $width. ' x '. $height;
      //echo '<br/><br/>File address: <b>http://'.$_SERVER['HTTP_HOST'].rtrim(dirname($_SERVER['REQUEST_URI']), '\\/').'/'.$uploadpath.'</b>';
        echo '<br><br><br> NOW COOPY THIS LINK';
      
    }
    else echo '<b>Unable to upload the file.</b>';
  }
  else echo $err;
}
?>
<div style="margin:1em auto; width:333px; text-align:center;">
 <form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="POST" enctype="multipart/form-data"> 

           
 <input type="text" value=<?php echo 'http://'.$_SERVER['HTTP_HOST'].rtrim(dirname($_SERVER['REQUEST_URI']), '\\/').'/'.$uploadpath.'';?> id="myInput">
 <button onclick="myFunction()">Copy text</button>
    
 <script>
function myFunction() {
 var copyText = document.getElementById("myInput");
  copyText.select();
    copyText.setSelectionRange(0, 99999)
     document.execCommand("copy");
    alert("Copied the text: " + copyText.value);
   }
  </script> 

<br><br>




 <form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="POST" enctype="multipart/form-data"> 
  Files uploader for DANMAKU CREATE<br>Allowed files: .png(max 1mb) .mp3(max 5 mb)<br><br> <input type="file" name="fileup" /><br/><br>
  <input type="submit" name='submit' value="Upload" /> 
 </form>
</div>