PaSh: Light-touch Data-Parallel Shell Processing

This paper presents scshape PaSh, a system for parallelizing POSIX shell scripts. Given a script, scshape PaSh converts it to a dataflow graph, performs a series of semantics-preserving program transformations that expose parallelism, and then converts the dataflow graph back into a script -- one that adds POSIX constructs to explicitly guide parallelism coupled with scshape PaSh-provided scshape Unix-aware runtime primitives for addressing performance- and correctness-related issues. A lightweight annotation language allows command developers to express key parallelizability properties about their commands. An accompanying parallelizability study of POSIX and GNU commands -- two large and commonly used groups -- guides the annotation language and optimized aggregator library that scshape PaSh uses. Finally, scshape PaSh's scshape PaSh's extensive evaluation over 44 unmodified scshape Unix scripts shows significant speedups (0.89--61.1×, avg: 6.7×) stemming from the combination of its program transformations and runtime primitives.