my $s = "line1\r\nline2\r\nline3\r\n";
     print $s;
     $s =~ s/[\n\r]//g;
     print $s;

##</code><code>##

     line1
     line2
     line3
     line1line2line3


##</code><code>##

   /s simply allows . to match end-of-line chars 
       anywhere in the string (if needed)
   /m simply allows ^ and $ to match begin/end
       of lines in mid-string instead of only
       the begin/end of the entire string.
   /g is happy to repeat searching over several lines
  m// (simple search) will find something that
       occurs on a line after the first one
   \n
   \r will both be found (if present) without
       resorting to /s or /m