simple monitoring of a directorys size, no rocket science

directory_size_watch.sh

#!/usr/bin/env bash
# DESC: simple monitoring of directory growth.. does a du and informs you the diff on a loop
# defaults to 300 second loop

# USAGE: this_script.sh "/some/directory/to/watch" is the directory to watch
# sample output:
#Fri May 13 13:12:06 BST 2016: thing grew by 132
#Fri May 13 13:17:07 BST 2016: thing grew by 83
#Fri May 13 13:37:07 BST 2016: thing shunk by 1575
#Fri May 13 13:42:07 BST 2016: thing grew by 596
#Fri May 13 13:47:07 BST 2016: thing grew by 536
#Fri May 13 13:52:07 BST 2016: thing grew by 368
#Fri May 13 13:57:07 BST 2016: thing grew by 3
#Fri May 13 14:02:07 BST 2016: thing grew by 7
#Fri May 13 14:07:07 BST 2016: thing grew by 7


#must be a dir
DEST="$1"
if [ ! -d "$1" ]; then
  echo "err.. please specify a dir"
  exit 1
fi

# Time between loops, as this is a dumb script the real time will include the time it takes "du" to stat also
TIME=300



get_size(){
  if [ -d "$1" ]; then
    du -sm "$1" | awk '{print $1}'
  else
    echo "sorry, $1 does not exist or is not a dir"
    exit 1
  fi
}

check_time(){
NOW="$(date)"
}



SIZE="$(get_size "$DEST")"



while true ; do
  OLD_SIZE=$SIZE
  check_time
  SIZE="$(get_size "$DEST")"
  DIFF="$(expr $SIZE - $OLD_SIZE)"

  if [ $DIFF -gt 0 ] ; then
    echo "$NOW: thing grew by $DIFF"
  fi
  if [ $DIFF -lt 0 ] ; then
    #strip the - from "$DIFF"
    DIFF="$(sed "s+-++g" <<<"$DIFF")"
    echo "$NOW: thing shunk by $DIFF"
  fi
#  if [ $DIFF == 0 ] ; then
#    echo no change
#  fi
  
#  echo "$NOW: $SIZE"
  sleep $TIME
done