forms - Prevent PHP script from being executed when submitting to self -

i have form:

<form name="commentform" id="commentform" action="comment.php" method="post"  enctype="multipart/form-data">  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 php validate 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 $_files["file"]["name"] . " exists. ";   } else   {   move_uploaded_file($_files["file"]["tmp_name"],   "upload/" . $_files["file"]["name"]);   echo "stored in: " . "upload/" . $_files["file"]["name"];   }   }   }   else   {   echo "invalid file";   }   ?> 

i submitting form same page, php executed webpage loads. how can make load form submitted? also, script not seem working.

you need check if form submitted before process file upload:

if ( isset($_post['pic'])) {    //save file here.  } 

edit: looks not referring right post variable - have file element called 'pic' in form referring $_post['file'] in php code not exist.

also: if starting out php, (imho) w3schools.com worse place can - i've seen bad examples of how code should not written in there..