To be more precise, my point was that you should only be targeting one of the implementations anyway. I don't see how it's a good use of people's time to be tes

To be more precise, my point was that you should only be targeting one of the implementations anyway. I don't see how it's a good use of people's time to be testing their scripts against every shell that claims to be sh-compatible, especially at a place like Google where the scripts are almost all being written to run on completely Google-controlled environments. But I didn't think about the bug vs. by-design issue and how that is remedied by a well-defined standard. That does seem to be a factor in favor of using a standardized language. But it doesn’t seem different in principle than depending on any software. It is liable to change and leave you with a difficult decision of forking the library or modifying your code that consumes it. Given bash’s ubiquity, it seems reasonable to expect a good level of stability. If you only target standards, the lowest-common-denominator of functionality, you will be poorer for it. Linux, for example, has all sorts of performance and functionality enhancing features over what POSIX provides.