#!/bin/bash

DIR=/tmp
CAPACITY_LIMIT=90
CAPACITY=$(df -k . | awk '{gsub("%",""); capacity=$5}; END {print capacity}')

# Delete oldest files until we're under limit
while [ $CAPACITY -gt $CAPACITY_LIMIT ] ; do
    find $DIR -type f -printf "%T@ %p\n" | sort -nr | tail -1 | cut -d' ' -f 2- | xargs -d '\n' rm
    # Delete empty dirs
    find $DIR -type d -empty -delete
    CAPACITY=$(df -k . | awk '{gsub("%",""); capacity=$5}; END {print capacity}')
done