Unix: octal \012       hex 0xA      dec 10      LF      may be \n
Dos:  octal \015\012   hex 0xD0xA   dec 13 10   CRLF    may be \r\n
Max:  octal \015       hex 0xD      dec 13      CR      may be \r

##</code><code>##

  $textfield =~ s/\015\012|\015|\012//g;

  If you prefer hex to octal :-)

  $textfield =~ s/\xD\xA|\xD|\xA//g;

##</code><code>##

  In expanded commented /x form:

  $textfield =~ s/         # substitute
                \015\012   # a CRLF sequence (DOS, MIME...)
                |          # or
                \015       # a lone LF (mac)
                |          # or   
                \012       # a lone LF (unix)
                /          # with literal ''
                /xg;       # /x allow comments, /g do globally