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Re: IFS field splitting doesn't conform with POSIX

From: Andreas Kusalananda Kähäri
Subject: Re: IFS field splitting doesn't conform with POSIX
Date: Thu, 30 Mar 2023 19:35:06 +0200

On Thu, Mar 30, 2023 at 10:51:58AM -0600, Felipe Contreras wrote:
> On Thu, Mar 30, 2023 at 10:10 AM Oğuz İsmail Uysal
> <oguzismailuysal@gmail.com> wrote:
> >
> > On 3/30/23 2:12 PM, Felipe Contreras wrote:
> > >      IFS=,
> > >      str='foo,bar,,roo,'
> > >      printf '"%s"\n' $str
> > zsh is the only shell that generates an empty last field, no other shell
> > exhibits this behavior.
> So? This is argumentum ad populum. The fact that most shells do X
> doesn't imply that POSIX says X.
> It could very well mean that all shells are implementing POSIX wrong.
> Except zsh.

Without getting into this *specific* issue: That's not how POSIX works.
POSIX standardises existing practices.


> Or it could mean POSIX doesn't specify which behavior is correct.
> > Besides your link says:
> >  >The shell shall treat each character of the IFS as a delimiter and use
> > the delimiters as *field >terminators* to split the results of parameter
> > expansion, command substitution, and arithmetic >expansion into fields.
> >
> > So the delimiters terminate fields, not separate them.
> Yes. 'foo,bar,' has two terminators, and therefore two fields.
> 'foo,bar,roo' has two terminators and therefore two fields, plus
> garbage.
> You want to interpret 'foo' as a field, even though it does not have
> an an explicit terminator. But that's not specified anywhere in POSIX.
> POSIX doesn't say what should be done with the text after the last
> terminator. You could throw it away and still be conforming to POSIX.
> -- 
> Felipe Contreras

Andreas (Kusalananda) Kähäri
SciLifeLab, NBIS, ICM
Uppsala University, Sweden


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