use warnings;
use strict;

my $read_memfile = <<'EOF';
one
two
three
EOF

open my $mem_fh, '<', \$read_memfile;
print $_ while(<$mem_fh>);
close $mem_fh;

my $write_memfile;

open my $mem_wfh, '>', \$write_memfile;
print $mem_wfh "hello, world!\n";
close $mem_wfh;

open my $str_fh, '<', \$write_memfile;
print $_ while (<$str_fh>);
close $str_fh;

__END__
one
two
three
hello, world!