$file='';
open(IN,"<$filename") || die "$file can't be opened: $!";
{ local $/=undef;  $file=<IN>; }
($\) = (/(\r\n|\r|\n)/);  # make output rec-separator same as input
@lines=split /[\r\n]+/, $file;
foreach $line (@lines) {
     # do some processing here
}