Note that the default being ISO-8859-1 may not
make sense for all content types, e.g.

  Content-Type: image/gif; charset=ISO-8859-1

In the above case you need to pass -charset => ''
to prevent the default being used.

##</code><code>##

# mycgi.pl
use CGI;
my $cgi = CGI->new;
print $cgi->header(
    -type       => 'application/vnd.ms-excel',
    #-nph        => 1,
    -expires    => '+3d',
    #-charset    => 'utf-8',
    -charset => '',
    -attachment => 'foo.xls',
);
# you need a foo.xls in your local dir
open (IMAGE, '<', 'foo.xls');
print <IMAGE>;
close IMAGE;

##</code><code>##

while true; do { echo -ne "HTTP/1.1 200 OK\r\n"; perl mycgi.pl; } | nc -l -k  8080; done