Re: Can't pipe output of pasta --version

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, May 27, 2025 at 05:21:19PM +0000, John Radley (jradxl2) wrote:
> Hello,I can't pipe output like this:-
> $ pasta --version | grep pasta<blank!>
> but this works:-
> $ sudo apt install expect
> $ unbuffer pasta --version | grep pasta
> pasta 2025_05_12.8ec1341-9-g3262c9b
> 
> If this is the intended action, please can you tell me why?

Ouch.  No, that's not intended.

I initially assumed this was because we were sending the version
information to stderr instead of stdout, but that's not the case.

This is a bug introduced by d0006fa78 ("treewide: use _exit() over
exit()").  For --version we're displaying the information with
fprintf(), then immediately exiting with _exit().  When writing to a
pipe, stdout is buffered.  Normally the buffer would be flushed before
exiting, but using _exit() bypasses that.

We could fix this specific problem by adding an fflush(stdout) before
the _exit().  However, I worry that there might be other bugs we have
because we're not running libc installed exit handlers here and
elsewhere.  I was already a bit dubious about using _exit() by
default, and now I really don't think it was a good idea.

That said, I don't immediately have a better idea of how to address
the problem d0006fa78 was aiming to fix in the first place.

Well... I'm on holiday at the moment, so I won't be fixing it.
Laurent & Stefano, I hope the analysis above is helpful.

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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