A bash while loop to get a URL from $PROTOCOL, $HOST and $DNS_DOMAIN environment variables.

get_url.sh

#!/bin/bash
DNS_DOMAIN=${DNS_DOMAIN:-example.com}
HOST=${HOST:-www}
HOSTNAME=$HOST.$DNS_DOMAIN
PROTOCOL=${PROTOCOL:-https}
URL=$PROTOCOL://$HOSTNAME
echo " --> Testing for $URL"
# Number of requests
TIMEOUT=30
# Time to wait between requests
SLEEP=1
# Initial HTTP code, should not be 200
HTTP_CODE=500
while [ $TIMEOUT -gt 0 -a $HTTP_CODE -ne 200 ]; do
  TIMEOUT=$[$TIMEOUT-1]
  HTTP_CODE=`curl -o /dev/null --silent --head --write-out '%{http_code}\n' $URL`
  if [ $HTTP_CODE == 200 ]; then 
    break 
  fi
  echo " --> GET $URL http_code:$HTTP_CODE ($[TIMEOUT-i] remaining) "
  sleep $SLEEP
done

if [ $HTTP_CODE == 200 ]; then 
  echo " --> GET $URL was successful"
  exit 0
else
  echo " --> All requests to $URL failed, aborting"
  exit 1
fi