bash script to free up disk space up to a threshold

ensure-free-space.sh

#!/bin/bash

dir="$1"
if [ ! -d "$dir" ]; then
    echo "$dir is not a directory.  Exiting."
    exit 1
fi

minimum="$2"
if [ -z "$minimum" ]; then
    minimum="5120000"
fi

function get_free {
    free=$(df -P "$dir" | tail -1 | awk '{print $4}')
}

get_free

while [ "$free" -lt "$minimum" ]
do
    oldest=$(find $dir -maxdepth 1 -mindepth 1 -type d -printf "%C@ %p\n" | grep -v 'lost+found' | sort | head -1 | awk '{print $2}')

    if [ -z "$oldest" ]; then
        echo "No directories remain in $dir - cannot reclaim enough space."
        exit 2
    fi

    echo "Removing: $oldest"

    /bin/rm -rf "$oldest"

    get_free
done

echo "$dir has more than $minimum blocks available"