aaa${  EXISTA  }aaa bbbBBBENVbbb cccCCCEQLccc
xxx${ NOEXISTX }xxx yyyyyy zzzZZZEQLzzz
aaa${  EXISTA  }aaa bbbBBBENVbbb cccCCCEQLccc
xxx${ NOEXISTX }xxx yyyyyy zzzZZZEQLzzz
unset variable with default value: ${NOEXISTX:-default}
even with basic syntax: CCCEQL.
