function check_download()
{
  if [ -f $DL/$FNAME ]; then
    CHECK=$(sha256sum $DL/$FNAME |awk '{printf $1};')
    if [ "$CHECK" == "$CSUM" ]; then
      return 0
    else
      echo "Checksum mismatch for $FNAME. Was $CHECK, expected $CSUM"
    fi
  else
    echo "$FNAME not found."
  fi

  return -1
}

function download()
{
  check_download && return 0

  rm -f $DL/$FNAME
  if [ -n "$URL" ]; then
    wget $URL -O $DL/$FNAME
  else
    echo URL must be specified
    exit 1
  fi

  check_download || return -1
}