Wait for DNS

Example.md

~ wait_for_dns.sh "google.com foobar.foo"                                                                                      Wed 15 Mar 2023 10:49:37 GMT

### Trying to resolve google.com foobar.foo ###
>> Waiting for dns 'google.com' to be available -> 172.217.16.238 2a00:1450:4009:821::200e 👍
>> Waiting for dns 'foobar.foo' to be available ----> Timed out after 4s 👎

wait_for_dns.sh

#!/bin/bash
set -eu

hosts=$1
lookup_retries=4
lookup_pause=2

echo -e "\n ### Trying to resolve $hosts ###"

for host in $hosts; do
  echo -n " >> Waiting for dns '$host' to be available "
  ip_addr=""
  counter=0
  while [ -z "${ip_addr}" ] && [ "${counter}" -lt "${lookup_retries}" ]; do
    echo -n "-"
    ip_addr=$(nslookup "$host" | awk '/^Address: / { print $2 }'  | tr '\n' ' ')
    [ -z "${ip_addr}" ] && sleep "${lookup_pause}"
    counter=$((counter+1))
  done
  if [ -z "${ip_addr}" ]; then
    echo "> Timed out 👎"
    exit 1
  else
    echo "> ${ip_addr}👍"
  fi
done

echo ""