First, /g means "global", which means search all the matching results, don't stop at the first one (either one result at a time, or all of them at once). This technically doesn't change anything, but you just need to find that there is one non-printable character to keep the string. So the first regex could just be /[^[:print:]]/.

The straightforward solution to your problem is to use an and rather than an or in your condition. You want a string that (only contains valid printable chars) AND (only contains valid non-space chars) => (does not contain non-printables) AND (does not contain spaces). De Morgan's laws might also be a good read on how to negate a condition with ORs and ANDs.

However, I think you can obtain something easier to read with unless (which is an "if not") and next which will stop processing the current element in a loop, and go on to the next.

# Delete the value and try the next one unless it has a non-printable,
+ or a space
delete $$hoh_ref{$key}{$value} and next unless /[^[:print:]]/ or /\s/;

while ($$hoh_ref{$key}{$value} =~ /([^[:print:]])/g)
{
  print "Unprintable !\n";
}
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