What’s new in POSIX 2024 – XCU

As of the previous release of POSIX, the Austin Group gained more control over the specification, having it be more working group oriented, and they got to work making the POSIX specification more modern. POSIX 2024 is the first release that bears the fruits of this labor, and as such, the changes made to it are particularly interesting, as they will define the direction of the specification going forwards. This is what this article is about!

Well, mostly. POSIX is composed of a couple of sections. Notably XBD (Base Definitions, which talk about things like what a file is, how regular expressions work, etc), XSH (System Interfaces, the C API that defines POSIX’s internals), and XCU (which defines the shell command language, and the standard utilities available for the system). There’s also XRAT, which explains the rationale of the authors, but it’s less relevant for our purposes today. XBD and XRAT are both interesting as context for XSH and XCU, but those are the real meat of the specification. This article will focus on the XCU section, in particular the utilities part of that section. If you’re more interested in the XSH section, there’s an excellent summary page by sortix’s Jonas Termansen that you can read here.
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The weekend isn’t over yet, so here’s some more light reading.