Continue from diotalevi's reply, you can actually just open it as if you are opening a normal file:

use warnings;
use strict;

my $str;
open FILE, ">", \$str;
print FILE "abcd\n";
print FILE "1234\n";
print $str;#the content is there before close
close FILE;
print $str; #the content is still there after close
[download]

Update - Just to add a more complete example with Net::Telnet:

You have to use your real host name, user name and password to make it work.

use Net::Telnet;

use warnings;
use strict;

my ($file, $str);
open $file, ">", \$str;
my $t = new Net::Telnet(timeout => 10, input_log => $file, Prompt => "
+/\[AAUA1\]/");
$t->open("foo");
$t->login("me", "hi");
$t->cmd("pwd");
$t->cmd("whoami");
$t->close();
print "\$str content:\n";
print $str;
[download]

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