transfer list in textarea to comma delimited string

hi, I have one textarea field in a registration form where visitor enters keywords. even there is a not next to the field "please enter keywords as comma delimited string", they enter as a list, below each other. I tried to convert the list into comma delimited string with several solutions but non of them works: $keywords = eregi_replace('\n', '.', $keywords); $keywords = eregi_replace('\r', '.', $keywords); $keywords = eregi_replace('\n\r', '.', $keywords); $keywords = eregi_replace('<br>', '.', $keywords); any help here? thanks -afan