Karl Matthias bio photo

Karl Matthias

DevOps, sysadmin, coder. Principal Systems Engineer at Nitro. Dublin, Ireland.




Magritte: Running sub-processes easily from Ruby

At MyDrive we have a few hefty binaries written in C++ that are used as part of our main telematics data processing pipeline.  One of these is built as a library and tied in to Ruby via FFI.  This C++ is all somewhat legacy code and the other binaries are built to pipe data in and out on the command line.  Rather than adapt them all to build as libraries, and write the FFI wrappers, I wrote a nice set of tooling to make it easy to run them as sub-processes from our pipeline workers.  It had a not very original name at first, but Gavin Heavyside suggested Magritte because of his painting The Treachery of Images, with the famous tag line Ceci n’est pas une pipe. “This is not a pipe”

So I released the Magritte gem on rubygems.org.

The idea is that you have some source of data and you want it to go somewhere just like a command line pipe.  The source needs to be a Ruby IO object and the output can either be an IO, or a block implementing your data handling routine.  I also provided a LineBuffer class to make it easy to write an output block that works on the output line by line.

Here’s an example of what you can do with it:

.out_to { |data| puts data }
.filtering_with('grep "relistan"')`

Much more information is available in the README on Github.

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