PaSh: light-touch data-parallel shell processing

This paper presents PaSh, a system for parallelizing POSIX shell scripts. Given a script, 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 PaSh-provided 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 PaSh uses. PaSh's extensive evaluation over 44 unmodified Unix scripts shows significant speedups (0.89--61.1×, avg: 6.7×) stemming from the combination of its program transformations and runtime primitives.