Delete oldest directory in another directory when hdd is out of space

clear_space.sh

#!/bin/bash
#
#  prune_dir - prune directory by deleting files if we are low on space
#
DIR=$1
CAPACITY_LIMIT=$2

if [ "$DIR" == "" ]
then
    echo "ERROR: directory not specified"
    exit 1
fi

if ! cd $DIR
then
    echo "ERROR: unable to chdir to directory '$DIR'"
    exit 2
fi

if [ "$CAPACITY_LIMIT" == "" ]
then
    CAPACITY_LIMIT=95   # default limit
fi

CAPACITY=$(df -k . | awk '{gsub("%",""); capacity=$5}; END {print capacity}')

if [ $CAPACITY -gt $CAPACITY_LIMIT ]
then

        while true; do

                # Find and delete the oldest file
                # in subdirectories of the directory
                find . -mindepth 2 -type d -printf '%T+ %p\n' | sort | awk 'NR==1{print $2}' | xargs r$

                # Check capacity
                CAPACITY=$(df -k . | awk '{gsub("%",""); capacity=$5}; END {print capacity}')

            if [ $CAPACITY -le $CAPACITY_LIMIT ]
            then
                # we're below the limit, so stop deleting
                exit
            fi

    done

fi