directory size reduced or gone

directory_size_reduced_or_gone.sh

#!/bin/bash

dir='/private/tmp'

if [ ! -d $dir ] ; then
  echo "the directory has gone"
  #echo 'body' | mailx -s "the directory has gone" [email protected]
  exit 1
fi

if [ -f /tmp/my_dir_size ] ; then
  old_size=`cat /tmp/my_dir_size | cut -f 1`
else
  old_size=0
fi

new_size=`du -sk $dir | cut -f 1`
echo $new_size > /tmp/my_dir_size

if [[ $old_size -eq 0 ]] ; then
  echo "no previous known size"
  #echo 'body' | mailx -s "no previous known size" [email protected]
  exit 1
fi

new_to_old_ratio=$(awk "BEGIN{print $new_size / $old_size}")
if [[ "$new_to_old_ratio" < '0.9' ]] ; then
  echo "new size less than 90% of previous ($new_to_old_ratio)"
  #echo 'body' | mailx -s "new size less than 90% of previous" [email protected]
  exit 1
fi

echo "new size is $new_to_old_ratio times the previous size"