By default, the Request Log Parser outputs header information to standard error before each file is processed. For example:

-------------------------------------------------------------------------
-- reqlogparser: Parsing 'my/path/dgraph1.log'...
-------------------------------------------------------------------------
/search?terms=pinot+noir&opts=mode+matchall&rank=0&offset=0&compound=1
/graph?node=8024&group=0&offset=0&nbins=10

[…]

-------------------------------------------------------------------------
-- reqlogparser: Parsing 'my/path/dgraph2.log'...
-------------------------------------------------------------------------
/search?terms=pinot+noir&opts=mode+matchall&rank=0&offset=0&compound=1
/graph?node=8024&group=0&offset=0&nbins=10

[…]

Using the --silent flag will suppress this information.