If you attempt to use telldir on an invalid directory handle, you'll get a "telldir() attempted on invalid dirhandle" warning

Also, telldir returns undef in such a case, so I'm thinking we could alternatively just test for definedness:

C:\_32>perl -le "open D, '<','test.txt' or die $!; print 'dir' if defi
+ned telldir D; print 'DONE';"
DONE

C:\_32>perl -le "opendir D, 'comp' or die $!; print 'dir' if defined t
+elldir D; print 'DONE';"
dir
DONE
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Of course, if it turns out that telldir was given something other than a handle, then it's a fatal error:

C:\_32>perl -le "open D, '<','test.txt' or die $!; print 'dir' if defi
+ned telldir $x; print 'DONE';"
Bad symbol for dirhandle at -e line 1.
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So that scenario would need to be avoided.

On *nix machines it shows the "." and ".." entries

Yes, it's the same on Windows.

Cheers,
Rob