#!/usr/bin/env sh
set -eu
url="${1:-https://example.com/}"
printf '== first request ==
'; curl -sS -D /tmp/headers-one -o /dev/null "$url"; grep -Ei '^(cache-control|etag|last-modified|vary|age):' /tmp/headers-one || true
etag=$(awk 'tolower($1)=="etag:"{$1="";sub(/^ /,"");gsub(/
/,"");print}' /tmp/headers-one)
[ -z "$etag" ] || curl -sS -o /dev/null -D - -H "If-None-Match: $etag" "$url" | head -n 1