On Wed, 24 Dec 2014 00:21:09 +0100 Harald van Dijk <harald@xxxxxxxxxxx> wrote: HvD> On 23/12/2014 23:34, Vadim Zeitlin wrote: HvD> > Hello, HvD> > HvD> > I'm not exactly sure if this is a bug because I didn't find any HvD> > specification about how is this supposed to behave (to my surprise it HvD> > turned out that $_ was not in POSIX), but please consider this: HvD> > HvD> > % zsh -c 'echo -n foo && echo $_' HvD> > foofoo HvD> > % bash -c 'echo -n foo && echo $_' HvD> > foofoo HvD> > % dash -c 'echo -n foo && echo $_' HvD> > foo/usr/bin/dash HvD> HvD> This does come across as somewhat confusing, but $_ is really not a HvD> special variable at all in dash. Ah, this does explain it, thanks! HvD> If dash did something special with $_, then I agree it would be nice if HvD> it would be somewhat compatible with other shells. If dash simply does HvD> not implement a feature, that feature is not required by any standard, HvD> and that feature is not widely used, then I suspect there won't be a lot HvD> of interest in implementing that feature. Yes, I understand, somehow the idea that dash didn't implement it at all just didn't occur to me, but clearly adding a non-standard new feature is not nowhere near as important as fixing [what looked like] a bug. I'm not sure about the "not widely part", but I don't have any non-anecdotal evidence one way or the other. HvD> Don't be put off by that, though. You are free, of course, if you feel HvD> so, to attempt to convince people $_ is an important feature that all HvD> shells should implement. If you have compelling use cases, if it solves HvD> real problems, and if many other shells already implement it, you might HvD> even get it standardised. I have never seen a need for it, but that's HvD> just me speaking from personal experience, others may feel differently. FWIW my initial problem started with using builddir := $(shell mkdir -p some-long-make-expression && echo $_) in a makefile, which seemed like a nice way to assign the value to the variable only if the directory was successfully created. This can, of course, be done in a myriad of other ways, but this one just seemed like the most elegant to me. Whether this counts as a "need" or not is not for me to say. Personally I'd say the main argument for adding support for "$_" to dash would be to avoid mysterious problems like the one I just had because dash silently (i.e. without giving any errors) behaves differently from the other shells, which in my case resulted in the makefile misbehaving only under Debian (where dash is used as /bin/sh) but not under systems. Anyhow, thanks again for your explanation! VZ
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