It seems like you're doing a lot of work for just looking for non-printable characters.  (Actually, they're ALL ascii characters, even the non-printable ones).  Also, I'm not sure why you're comparing with 121; the printable characters go all the way to 127 126 (= "~").  (Thanks ambrus, I knew that, but somehow my thinking was "off by one").

Instead of sorting, how about just applying the test to each character in the line?  Here's a subroutine which will return nonzero if the line contains non-printable characters, and zero otherwise:

sub line_contains_non_printable {
    my ($line) = @_;
    my @split = split //, $line;
    foreach (@split) {
        my $ord = ord($_);
        return 1 if ($ord < 32 || $ord > 126);
    }
    return 0;
}
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I'm sure there's at least several good modules for doing this as well (that I don't know of offhand), which other monks may be able to recommend.