Keep n newest directories deleting all older in a specified directory

gistfile1.sh

#!/usr/bin/env bash

dir="$1"
min_dirs=5

exclude=$(readlink -f $(find "$dir" -maxdepth 1 -type l))

while [ $(find "$dir" -maxdepth 1 -type d -not -path $exclude | wc -l) -gt $min_dirs ] && IFS= read -r -d $'\0' line < <(find "$dir" -maxdepth 1 -type d -not -path $exclude -printf '%T@ %p\0' 2>/dev/null | sort -z -n);
do
        file="${line#* }"
        ls -1Ld "$file" | xargs rm -r
done