...
my $fh_in = $cgi->upload('file');
binmode $fh_in, ':encoding(UTF-8)';

open(my $fh_out, '>:encoding(UTF-8)', "/var/www/mypath/$filename")
   or die $!;

while (<$fh_in>) {
   print $fh_out $_;
}

##</code><code>##

...
my $fh_in = $cgi->upload('file');
open(my $fh_out, '>', "/var/www/mypath/$filename")
   or die $!;

while (<$fh_in>) {
   print $fh_out $_;
}

##</code><code>##

...
my $fh_in = $cgi->upload('file');
open(my $fh_out, '>', "/var/www/mypath/$filename")
   or die $!;

binmode $fh_in;
binmode $fh_out;

local $/ = \4096;  # Don't wait to find "\n"
while (<$fh_in>) {
   print $fh_out $_;
}