readlink -f is GNU coreutils only (used in bin/hive)

  bin=`dirname "$0"`
  # many hadoop installs are in dir/{spark,hive,hadoop,..}
  sparkHome=$(readlink -f $bin/../../spark)

uses -f which means canonicalize in GNU coreutils and format in BSD coreutils.

This needs a wrap-around test -e to prevent invocation against non-existent spark installs.