Anyone know of way to convert the characters like linefeed, carrier return, etc.

Hi! Does anyone know how to use the php code to identify the character like linefeed or carrier return or space, etc.? I'm making a loop to identify those and replace it with a HTML characters so the data would be HTML compactible. For example, replacing the line feed with a "<br>", etc. The only problem is I can not tell what characters are in there because it is not readable by the web browser. I hope I explained it clear enough. Thanks, Scott