ICQ chat bot problems with encodings - perl

Question

Yesterday I have been writing simple program in perl.
It is icq bot, you write a message as the math expression and it calculates the value.
The problem is that incoming message has not-single-byte encoding and when it is writing
to file there are a lot of bad symbols and of course calc can't handle this file.
how can I convert incoming message to ASCII?
Here is the source:
#!/usr/bin/perl
use Net::OSCAR;
use Encode;
use strict;
my ($UIN, $PASSWORD, $oscar, $t, $msg);
$UIN='675349295';
$PASSWORD='passwd';
$oscar = Net::OSCAR->new();
$oscar->set_callback_im_in(\&send_answer);
$t = 0;
while (1)
{
if (!$oscar->is_on && (time() - $t) > 120)
{
$oscar->signon($UIN, $PASSWORD);
$t=time();
}
$oscar->do_one_loop();
}
sub send_answer()
{
my($oscar, $sender, $msg) = #_;
if ($msg eq "quit")
{
$oscar->signoff();
exit();
}
open(my($fh), '>', '/tmp/msg');
print $fh "$msg";
close $fh;
my($ans)=`calc -p -f /tmp/msg`;
$oscar->send_im($sender, $ans);
}