#!/bin/bash

if [ -z "$1" ]; then
  echo "Prints <used>/<available> space at <MOUNT_DIR> in full bytes"
  echo "    Usage: $0 <MOUNT_DIR>"
  exit 1
fi

FACTORS=('' 'K' 'M' 'G' 'T' 'P')
BLKSIZE=$(df | sed -n '1 p' | awk '{print $2}' | sed 's/-blocks//') # e.g. "1K", "2M", "512K"

REG='([0-9]+)([KMGTP]?)'
[[ $BLKSIZE =~ $REG ]]
BLKBASE="${BASH_REMATCH[1]}"
BLKEXP="${BASH_REMATCH[2]}"

for i in "${!FACTORS[@]}"; do
  if [[ "${FACTORS[$i]}" = "${BLKEXP}" ]]; then
    BLKEXP=$i
  fi
done

BLKSIZE=$[($BLKBASE*(2**(10*$BLKEXP)))]

MOUNT=$1
DF_LINE=( $(df | tail -n +2 | grep "$MOUNT\$" | awk '{printf "%s %s", $3, $2}') )

if [ -z "$DF_LINE" ]; then
  exit 0
fi

USED=$[${DF_LINE[0]}*$BLKSIZE]
AVAIL=$[${DF_LINE[1]}*$BLKSIZE]

echo $USED"/"$AVAIL