title: Output from just "tab" command in Scala REPL (not autocompletion)
body: <p>I was playing around with <code>scala REPL</code> and <code>spark-shell</code> and came along this. So, in the scala REPL or spark-shell if you just hit <code>tab</code> it outputs like the following: </p>
  
  <pre><code>scala&gt; 
  &lt;init&gt;                           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                                
  </code></pre>
  
  <p>which also includes all the variables/objects I defined. The above output is from the cluster terminal. But when I do it from local computer (ie use scala REPL in local computer), it also outputs the directories/files in the directory I am at while opening the REPL. </p>
  
  <p>Could someone explain, what this <code>tab</code> command is actually doing here? </p>