Thanks! Here's that command line explained bit by bit:

grep         grep for
-v           lines that DO NOT match
^$           an empty line (begin and end with nothing between)
inputfile    in the file "inputfile"
|            pipe the results to
split        the split program, which divides up a file
-d           naming the output files with digits
-l 300000    and putting 300000 lines in each
-            getting the input from stdin (the pipe)
outputfile   and naming the output files starting with outputfile (fol
+lowed by digits)
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