monitor remaining days before ssl certificate expiration

ssl-days.sh

#!/bin/bash
set -eu

if (( $# < 1 )); then
  echo "usage: $0 <host:port> [<host:port> ...]"
  exit 1
fi

me=$(basename "$0")
HOSTNAME="${COLLECTD_HOSTNAME:-localhost}"
INTERVAL="${COLLECTD_INTERVAL:-60}"
cache_file="/tmp/tmp.$me"

function ssl_end_days() {
  host=$1
  end_date_txt=$(echo | timeout 1 openssl s_client -connect "$host" 2> /dev/null | openssl x509 -noout -enddate 2> /dev/null | sed -e 's/.*notAfter=\(.*\)/\1/')
  diff_days=$(( ($(date -d "$end_date_txt" +%s) - $(date +%s)) / 86400 ))
  echo $diff_days
}

echo "$cache_file"
while true; do
  echo -n '' > "$cache_file"
  for arg in "$@"
  do
    VALUE=$(ssl_end_days "$arg")
    echo "PUTVAL \"$HOSTNAME/exec-$me/$arg\" interval=$INTERVAL N:$VALUE" >> "$cache_file"
  done

  sleep 3600
done &

while sleep "$INTERVAL"; do
  cat "$cache_file"
done