Based on what you posted, this:

push @files , grep { -f  && -s >= $min_size && -s <= $max_size "$d
+/$_" } read_dir($d);
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becomes:

push @files , map { "$d/" . $_} grep { -f  && ( -s >= $min_size) && (-
+s <= $max_size) } read_dir($d);

#this is untested.
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