In this example batch pipeline we will invoke a simple Echo C++ library within a DoFn The sample
makes use of a ExternalLibraryDoFn class which abstracts the setup and processing of the
executable, logs and results. For this example we are using commands passed to the library based
on ordinal position but for a production system you should use a mechanism like ProtoBuffers with
Base64 encoding to pass the parameters to the library To test this example you will need to build
the files Echo.cc and EchoAgain.cc in a linux env matching the runner that you are using (using
g++ with static option). Once built copy them to the SourcePath defined in
SubProcessPipelineOptions