Prevent PHP script from being executed when submitting to self

I have this form:

<form name="commentform" id="commentform" action="comment.php" method="post" 
enctype="multipart/form-data">

Your Name: 
<textarea maxlength="60" rows="1" cols="62" class="margin" name="name" 
id="name"> </textarea> <br><br>

Submit Picture
<input type="file" name="pic" id="pic" /> <br><br>

<input type="Submit" value="Submit" />
</form>

This is the PHP to validate the picture (from W3Schools.com):

<?php
if ((($_FILES["file"]["type"] == "image/gif")
|| ($_FILES["file"]["type"] == "image/jpeg")
|| ($_FILES["file"]["type"] == "image/pjpeg"))
&& ($_FILES["file"]["size"] < 20000))
{
if ($_FILES["file"]["error"] > 0)
{
echo "Return Code: " . $_FILES["file"]["error"] . "<br />";
}
else
{
echo "Upload: " . $_FILES["file"]["name"] . "<br />";
echo "Type: " . $_FILES["file"]["type"] . "<br />";
echo "Size: " . ($_FILES["file"]["size"] / 1024) . " Kb<br />";
echo "Temp file: " . $_FILES["file"]["tmp_name"] . "<br />";

if (file_exists("upload/" . $_FILES["file"]["name"]))
  {
  echo $_FILES["file"]["name"] . " already exists. ";
  }
else
  {
  move_uploaded_file($_FILES["file"]["tmp_name"],
  "upload/" . $_FILES["file"]["name"]);
  echo "Stored in: " . "upload/" . $_FILES["file"][开发者_开发知识库"name"];
  }
  }
  }
  else
  {
  echo "Invalid file";
  }
  ?>

I am the submitting the form to the same page, so the PHP is executed as soon as the webpage loads. How can I make it load as soon as the form is submitted? Also, this script does not seem to be working.

You need to check if your form is submitted before you process the file upload:

if ( isset($_POST['pic'])) {

  //save file here.

}

EDIT: It looks like your not referring to the right POST variable - you have a file element called 'pic' in your form but you are referring to $_POST['file'] in your PHP code which will not exist.

Also: If you are starting out with PHP, (IMHO) W3Schools.com is the worse place you can be - I've seen really bad examples of how code should NOT be written in there..

<?php

if( isset( $_POST( 'submit' ) ) ){ // Check form is submitted or not 

if ((($_FILES["file"]["type"] == "image/gif")
|| ($_FILES["file"]["type"] == "image/jpeg")
|| ($_FILES["file"]["type"] == "image/pjpeg"))
&& ($_FILES["file"]["size"] < 20000))
{
if ($_FILES["file"]["error"] > 0)
{
echo "Return Code: " . $_FILES["file"]["error"] . "<br />";
}
else
{
echo "Upload: " . $_FILES["file"]["name"] . "<br />";
echo "Type: " . $_FILES["file"]["type"] . "<br />";
echo "Size: " . ($_FILES["file"]["size"] / 1024) . " Kb<br />";
echo "Temp file: " . $_FILES["file"]["tmp_name"] . "<br />";

if (file_exists("upload/" . $_FILES["file"]["name"]))
  {
  echo $_FILES["file"]["name"] . " already exists. ";
  }
else
  {
  move_uploaded_file($_FILES["file"]["tmp_name"],
  "upload/" . $_FILES["file"]["name"]);
  echo "Stored in: " . "upload/" . $_FILES["file"]["name"];
  }
  }
  }
  else
  {
  echo "Invalid file";
  }
}
  ?>

Add This To the Top of your page:

<?php $action = $_GET['action']; ?>

Your New Form:

<form name="commentform" id="commentform" action="comment.php?action=go" method="post" enctype="multipart/form-data">
Your Name: <textarea maxlength="60" rows="1" cols="62" class="margin" name="name" id="name"> </textarea> <br><br>

Submit Picture<input type="file" name="pic" id="pic" /> <br><br>
<input type="Submit" value="Submit" />
</form>

And the action script:

<?php
if (isset($action) && $action == 'go'){
if ((($_FILES["file"]["type"] == "image/gif") || ($_FILES["file"]["type"] == "image/jpeg") || ($_FILES["file"]["type"] == "image/pjpeg")) && ($_FILES["file"]["size"] < 20000)) {
if ($_FILES["file"]["error"] > 0){
echo "Return Code: " . $_FILES["file"]["error"] . "<br />";
}else{
echo "Upload: " . $_FILES["file"]["name"] . "<br />";
echo "Type: " . $_FILES["file"]["type"] . "<br />";
echo "Size: " . ($_FILES["file"]["size"] / 1024) . " Kb<br />";
echo "Temp file: " . $_FILES["file"]["tmp_name"] . "<br />";
if (file_exists("upload/" . $_FILES["file"]["name"]))  {
echo $_FILES["file"]["name"] . " already exists. ";  
}else{  
move_uploaded_file($_FILES["file"]["tmp_name"],  "upload/" . $_FILES["file"]["name"]);  
echo "Stored in: " . "upload/" . $_FILES["file"]["name"];  
}  
}  
}else{  
echo "Invalid file";  
}  
}
?>