use strict;
use warnings;

my $mf;
my $fh;

# mem write

open $fh, '>', \$mf or die $!;
print $fh "hello\n";
close $fh;

# mem read

open $fh, '<', \$mf or die $!;
binmode $fh, ':raw';

while (<$fh>){
    print "mem: " . (unpack "H*", $_) . "\n";
}
close $fh;

# file write

open $fh, '>', 'file.txt' or die $!;
print $fh "hello\n";
close $fh;

# file read

open $fh, '<', 'file.txt' or die $!;
binmode $fh, ':raw';

while (<$fh>){
    print "file: " . (unpack "H*", $_) . "\n";
}

##</code><code>##

mem:  68656c6c6f0a
file: 68656c6c6f0d0a