LockScreenSaverOnUSBDisconnect.sh

#!/usr/bin/env bash
FILTER_YUBIKEY='/Yubikey/{print;getline;getline;print;getline;print}'
EXPECTED_YUBI_MD5="1a067fac7f6915a0acd5a235876fd33e" # Hash of USB Device
LONG_POLL_TIME=3  # Poll time after locking
SHORT_POLL_TIME=1 # Poll time while waiting for yubikey to disconnect
ARMED=0
DATESTRING=%Y-%m-%d\ %H:%M:%S.000

do_screen_saver() {
  echo "`date \"+${DATESTRING}\"` locking screen"
  find /System/Library \
    -type d ! \
    -perm -o+r \
    -prune -o \
    -name "ScreenSaverEngine" \
    -exec {} \; \
    -quit
}

while [[ true ]]; do
  ACTUAL_YUBI_MD5=`system_profiler SPUSBDataType | awk $FILTER_YUBIKEY | md5`

  if [[ "${EXPECTED_YUBI_MD5}" != "${ACTUAL_YUBI_MD5}" ]]; then
    if [[ "${ARMED}" -eq 1 ]]; then
      ARMED=0
      do_screen_saver
    fi
    sleep $LONG_POLL_TIME
  elif [[ "${ARMED}" -eq 0 ]]; then
    echo "`date \"+${DATESTRING}\"` arming"
    ARMED=1
  else
    sleep $SHORT_POLL_TIME
  fi
done