Your map is in void context, it is not used for anything but a fancy loop. I think the logic of the @maxreject array is flawed, but I'm not sure what you're trying to accomplish with it.

I suspect you want (split ' ') where you break a line into an array.

Update: Ah, in that case, I'd keep an array of the column indexes to tag (supposing there may be more than one) and do this:

my @tagthese = (4,5,6);
# ... down in the read loop
    for (@data[@tagthese]) {
        $_ = '?' . $_ if $_ < $minclip or $_ > $maxclip;
    }
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After Compline,
Zaxo