> POSIX hasn't provided a way to validate whether a script > only uses features that are required to be supported by POSIX > compliant interpreters.
I believe that was someone else's point, but yes that would be a problem for anyone who wanted to implement compliance check warnings. > even if bash is technically compliant with POSIX, what use case is usefully > served by having bash support a superset of the POSIX test operators while executing in POSIX mode? It's a matter of practicality and the fact that nobody has written it yet. If you wanted to implement conformance checks without making Bash even bigger and slower, and harder to maintain, I don't think there would be objections. Bash just modifies conflicting features to the minimal extent necessary to bring it into compliance, which seems to be the path of least resistance. This would be a big job, I think, and not quite at the top of my wish-list. Right now you can increase the number of things that fail by explicitly disabling non-POSIX built-ins using the Bash "enable" builtin. > I wasn't claiming that static checking would be viable. In fact, the > impossibility of static checking is precisely why it would be useful > to have real POSIX "compliant" interpreters that were as conservative > as possible in the syntax and commands they accepted at least in their > so-called POSIX mode. Dash is useful for testing. The Bash answer is [[, which CAN do a lot of special error handling on due to it being a compound command. I wrote a bit about this here: http://mywiki.wooledge.org/BashFAQ/031/#Theory In reality, [[ is one of the very most portable non-POSIX features available. Most people shouldn't have to worry about avoiding it. On Sunday, May 27, 2012 11:09:03 PM Jon Seymour wrote: > That said, from the point of view of promoting interoperable scripts, > my view is that it (in an ideal world**) would be better if bash chose > to fail, while executing in POSIX mode, in this case. In an ideal world, POSIX would define [[, Dash wouldn't exist, and we would have some resource other than POSIX that specifies what's ACTUALLY portable between modern shells, so that the only people who have to worry are those targeting Busybox and Solaris Heirloom, or stubborn curmudgeons who insist on Dash... some of these things feel like supporting IE6 - it's better to just not. > This is exactly my problem: I replaced /bin/sh -> dash with /bin/sh -> > bash because a 3rd party product installation script failed when dash > was the "POSIX" shell. If you need a fast small shell, use mksh. It supports some of the more essential features of both Bash and Ksh (arrays, ((, [[), and some of its own, without all the draconian restrictions of dash. (Note this is querying my package manager, including symbols and source files) # equery s dash * app-shells/dash-0.5.7.1 Total files : 73 Total size : 1.14 MiB # equery s mksh * app-shells/mksh-9999 Total files : 39 Total size : 1.61 MiB # equery s bash * app-shells/bash-4.2_p28 Total files : 464 Total size : 6.33 MiB -- Dan Douglas
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