This is a good reason for having an editor that highlights code, last week there was a similar question with the identical data and same backslash error, and since it is a tutorial then unless the author is trying to let users know not to do that then there needs to be a way of letting him know that his tutorial needs fixing.
The array name$ junk and all chars in the array were identical and actually just by posting it here in these forums showed the error rather quickly. So I then ran it through an editor and found the best way to prevent errors was with double quotes other wise you also has a single quote with single quotes so this will work
<?php
$junk = array("." , "," , "/" , "\\" , "`" , ";" , "[" , "]" , "-",
"*", "&", "^", "%", "$", ",", "@", "!", "~", "+", "(", ")",
"|", "{", "}", "<", ">", "?", ":", "'", "=");
echo "<pre>";
print_r ($junk);
?>