Script to sync a local directory to external hard drive

sync_me

#!/usr/bin/env bash

# This will sync LOCAL_DIR directory to XTAL_DIR (which is my xtal hard drive)
# It's meant to run on frequent polling cron job so that it syncs "immediately"
# when the xtal is plugged in.  It will do nothing if the xtal drive is not
# plugged in.

# After a successful sync, it will change the crontab so it is not sync'd again
# for 24 hours. This script assumes you don't need more frequent backing up than
# that because I use it for my projects directory where everything important is
# in a hosted git repo anyway. When it detects the hard drive to be disconnected
# by the failed "ls" command, it will then revert back to frequently polling.

# To start this process, just run "./sync_me -b" (b is for boot)

LOCAL_DIR=/Users/macbookair/Projects/
XTAL_DIR=/Volumes/LaCie/Projects
LOG_FILE=/tmp/cron.sync_me.log
COMMAND="$(pwd)/sync_me -x >> ${LOG_FILE} 2>&1"

SHORT_CRON="*/2 * * * * ${COMMAND}" # every 2 minutes
LONG_CRON="0 0 * * * ${COMMAND}" # every day at midnight

function write_cron {
  local CRON_STRING="$1"
  local CRON_FILE="$(pwd)/.sync_me.cron"

  crontab -l > "$CRON_FILE"
  echo "$CRON_STRING" > "$CRON_FILE"
  crontab "$CRON_FILE"
  rm "$CRON_FILE"
}

if [ "$1" == "-b" ]; then
  write_cron "$SHORT_CRON"
  exit
fi

if [ -d "$XTAL_DIR" ]; then
  # External is pluggged in
  if [ "$1" == "-x" ]; then
    rsync -ra $LOCAL_DIR $XTAL_DIR
    write_cron "$LONG_CRON"
  else
    # Dry run
    rsync -ranv $LOCAL_DIR $XTAL_DIR
  fi
else
  # External is not plugged in, poll
  write_cron "$SHORT_CRON"
fi