Remove oldest .tgz files, if free space less than 50GB

remove_oldest_files.sh

#!/usr/bin/env bash
# set -o nounset
set -o errexit
shopt -s dotglob

# Remove oldest .tgz files, if free space less than 50GB
#
# License: CC0 1.0 or newer
# https://creativecommons.org/publicdomain/zero/1.0/
#
# You can download this script here: https://gist.github.com/vazhnov/177fa8dfb474ed108860731dca21c591

dir="/tmp"

while [ $(df --output=avail ${dir} | tail -n 1) -lt 50000000 ]; do
  # See for details: http://mywiki.wooledge.org/BashFAQ/003
  unset -v oldest
  for file in "$dir"/*tgz; do
    [[ -z $oldest || $file -ot $oldest ]] && oldest=$file
  done

  rm -f "${oldest}"
done

Another logic: delete oldest file if there are more than 6 files in the current working directory: https://gist.github.com/maximiliankolb/ab6670d3bd86fa91af7aac42c646cd77