Re: Putting fifos in subshells into the background
Philip Guenther wrote:
> On Wed, Jun 12, 2019 at 12:54 AM Richard Ulmer
> wrote:
>
> > while making the Kakoune editor work on OpenBSD, I encountered some
> > strange behaviour [1]. This little script doesn't work with the OpenBSD
> > sh, but works at least with dash, bash and zsh:
> >
> > mkfifo 'testfifo'
> > cat "$(
> > ( printf 'foo\n' > testfifo 2>&1 ) > /dev/null 2>&1 &
> > printf 'testfifo'
> > )"
> >
> > I can make it work for all the mentioned shells like this:
> >
> > mkfifo 'testfifo'
> > cat "$(
> > ( ( printf 'foo\n' > testfifo 2>&1 ) & ) > /dev/null 2>&1
> > printf 'testfifo'
> > )"
> >
> > Can someone explain or justify the behaviour of the OpenBSD sh, or do
> > you think this is a bug?
> >
>
> This is a bug, almost certainly from an over-zealous optimization in the
> logic handling subshells where the possibility that an inner redirection
> could be blocking wasn't taken into account when it tries to avoid
> unnecessary forks.
Thanks for the clarification! I'll note your assessment on the issue for
Kakoune.
> Sorry, I don't have a fix in my back pocket. Your workaround is good; I'll
> note the intermediate set of parens can also be braces, which would let you
> avoid the otherwise necessary whitespace between open-parens if that grates
> on your soul like it does mine. :)
I feel you, but I'm afraid our souls will keep getting grated, because
unfortunately bash and the like won't work if I use `{}` instead of the
intermediate `()`. I guess this is a bug of thes other shells then.
Thanks for your help!
Richard Ulmer
Re: Putting fifos in subshells into the background
On Wed, Jun 12, 2019 at 12:54 AM Richard Ulmer wrote: > while making the Kakoune editor work on OpenBSD, I encountered some > strange behaviour [1]. This little script doesn't work with the OpenBSD > sh, but works at least with dash, bash and zsh: > > mkfifo 'testfifo' > cat "$( > ( printf 'foo\n' > testfifo 2>&1 ) > /dev/null 2>&1 & > printf 'testfifo' > )" > > I can make it work for all the mentioned shells like this: > > mkfifo 'testfifo' > cat "$( > ( ( printf 'foo\n' > testfifo 2>&1 ) & ) > /dev/null 2>&1 > printf 'testfifo' > )" > > Can someone explain or justify the behaviour of the OpenBSD sh, or do > you think this is a bug? > This is a bug, almost certainly from an over-zealous optimization in the logic handling subshells where the possibility that an inner redirection could be blocking wasn't taken into account when it tries to avoid unnecessary forks. Sorry, I don't have a fix in my back pocket. Your workaround is good; I'll note the intermediate set of parens can also be braces, which would let you avoid the otherwise necessary whitespace between open-parens if that grates on your soul like it does mine. :) Philip Guenther
Putting fifos in subshells into the background
Hi, while making the Kakoune editor work on OpenBSD, I encountered some strange behaviour [1]. This little script doesn't work with the OpenBSD sh, but works at least with dash, bash and zsh: mkfifo 'testfifo' cat "$( ( printf 'foo\n' > testfifo 2>&1 ) > /dev/null 2>&1 & printf 'testfifo' )" I can make it work for all the mentioned shells like this: mkfifo 'testfifo' cat "$( ( ( printf 'foo\n' > testfifo 2>&1 ) & ) > /dev/null 2>&1 printf 'testfifo' )" Can someone explain or justify the behaviour of the OpenBSD sh, or do you think this is a bug? Cheers, Richard Ulmer [1] See https://github.com/mawww/kakoune/pull/2955 for more info.
