我正在玩scala REPL和spark-shell而且还来了。所以，在scala REPL或spark-shell中，如果你只是点击tab，它输出如下：
scala>
<init> DRIVER_IDENTIFIER Level Logger MatchTest1 MatchTest2 NAStatCounter
SPARK_JOB_DESCRIPTION SPARK_JOB_GROUP_ID SPARK_JOB_INTERRUPT_ON_CANCEL SPARK_UNKNOWN_USER StatCounter arr boolToBoolWritable
booleanWritableConverter bytesToBytesWritable bytesWritableConverter classOf clearActiveContext clone cons
doubleRDDToDoubleRDDFunctions doubleToDoubleWritable doubleWritableConverter eq equals finalize floatToFloatWritable
floatWritableConverter getClass hashCode intToIntWritable intWritableConverter isTraceEnabled jarOfClass
jarOfObject log logDebug logError logInfo logName logTrace
logWarning longToLongWritable longWritableConverter ls markPartiallyConstructed nas nas1
nas2 ne notify notifyAll numericRDDToDoubleRDDFunctions rddToAsyncRDDActions rddToOrderedRDDFunctions
rddToPairRDDFunctions rddToSequenceFileRDDFunctions res0 res1 res10 res13 res14
res17 res18 res2 res22 res24 res25 res26
res27 res28 res3 res31 res32 res33 res35
res36 res37 res39 res4 res41 res42 res5
res6 res7 res8 res9 sc setActiveContext stringToText
stringWritableConverter synchronized toString updatedConf wait writableWritableConverter x
还包括我定义的所有变量/对象。以上输出来自集群终端。但是，当我从本地计算机（即在本地计算机中使用scala REPL）执行此操作时，它还会在打开REPL时输出我所在目录中的目录/文件。
有人可以解释一下，这个tab命令实际上在这里做了什么？