You can click "Disable smilies in text" option when you post. I edited your post to do that. Don't know why you're having trouble and I can't test in your environment but [:alnum:] is all letters and numbers. Try that. [:print:] is anything you can see, which is not what you want here. You want to discard some visible characters but keep others. Another thing to try is [a-z][A-Z][0-9] It's supposed to work without the brackets by some very old versions of tr required brackets for a range.