If you are looking for which domain point to 1.2.3.4: cat domains.txt | parallel -P 100 --tag host | grep 1.2.3.4 Somewhat slower runtime than the go-solut

If you are looking for which domain point to 1.2.3.4: cat domains.txt | parallel -P 100 --tag host | grep 1.2.3.4 Somewhat slower runtime than the go-solution, but may be faster to write.