my %badchars;
while (<>) {
    my @bad = ( /([^[:ascii:]])/g ); # find all bad characters
    if ( @bad ) {
        for my $badch ( @bad ) {
            $badchars{$badch}++;
        }
        my $badlist = join ' ', map { sprintf("%02x", ord{$_}) } @bad
        warn "line contains bad char(s) ($badlist): $_";
    }
}
for my $badch ( sort keys %badchars ) {
    printf "%6d %02x %s\n", $badchars{$badch}, ord($badch), $badch;
}