#!/bin/bash
# script-friendly df

factor=1024  # default

OPTSTRING="H"
while getopts ${OPTSTRING} opt; do
  case ${opt} in
    H)
      factor=1000
      ;;
  esac
done
shift $((OPTIND-1))

target=${1:-.}

free_bytes=$(findmnt --df -T "$target" -oAVAIL --bytes | sed '1d')
free_gigs=$((free_bytes/(factor**3)))
echo $free_gigs