# 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;