检测小写和大写的PHP之间

I am using this script to delete picture from my server. But at the same time I want to protect the files in my server. Not accidentally delete but I noticed that if I typed the file index.pHp or index.Php is deleted from my server. Although setting it will not delete why php or this method not know between lowercase and uppercase.

What is not done right?

<?php
error_reporting (0);
$thefile = $_GET ['filetodel'];
$filename = "$thefile";
//$filename = "picture1.jpg";

/*protect some files*/
if ($thefile=='index.php' or $thefile=='INDEX.PHP' or $thefile=='UPLOADS.ZIP' or $thefile=='uploads.zip' or $thefile=='del.php'or $thefile=='DEL.PHP' or $thefile==NULL or $thefile=='.htaccess' or $thefile=='.HTACCESS' )
{
exit("<h2>cannot delete $thefile</h2>");
}
if ($thefile=="$thefile")
{
if (file_exists($filename))
{
unlink ("$thefile");
echo "<h2> file $thefile is delete</h2>";
} 
else 
{
echo "<h2>The<br>";
echo "$filename<br>";
echo "Does not exist</h2>";
}
}
?>

Just convert the input to lowercase and test it once, rather than worrying about every possible mix of case:

if (strtolower($thefile) == 'index.php') {
  // ...
}

For the next iteration, you could store your protected files in an array:

$protected_files = array('index.php', 'uploads.zip', 'del.php', '.htaccess');

if (in_array(strtolower($thefile), $protected_files) || $thefile==NULL) {
  // ...
}

the problem is here:

if ($thefile=="$thefile")

as if your 1st condition for file check is false than the second condition is

if ($thefile=="$thefile")

which is always true so it will unlink the file Also add one line as below just before 1st condition

$thefile = strtolower($thefile);