[Toybox] xargs with blank input

[Rob Landley]

On 10/16/2013 11:35:15 PM, Robert Thompson wrote:
> Not that it's really relevant to most linux environments, but the OSX
> version (with a BSD manpage) appears to not execute any commandline  
> that
> would have no added arguments. A quick test suggests this is true for  
> both
> normal and null-separated modes.
> 
> Specifically, echo "" | xargs echo foo; echo "returned $?" will output
> exactly one line: "returned 0", instead of the two lines seen on my  
> debian
> test box. On the other hand, echo "bar" | xargs echo foo; echo  
> "returned
> $?" behaves identically on both machines.

William implied that there were package builds that failed with the  
previous toybox behavior? (It would be nice to know what those were.)

I keep forgetting that the default of xargs is "echo" and thus piping  
things into "xargs echo" myself when I want to collate lots of lines  
onto a single line.

> The manpage mentions that "The xargs utility is expected to be IEEE  
> Std
> 1003.2 (``POSIX.2'') compliant.", for what it's worth.

Posix has holes you could drive a truck through. Its failure mode is  
failing to specify stuff. (As failure modes go, that's a good one, but  
the way it pretends mount and init don't exist is kinda annoying.)

> It appears that they are reading the "shall construct ..." to  
> instruct that
> if no arguments are read, there is no complete commandline, thus the  
> xargs
> terminates without ever trying to launch a process, but without any  
> error.

Would a good rule be "if the input had a newline, we got a command  
line. If the input was literally no data, we didn't"?

> My tests on current osx 10.8 indicate that xargs never execs the  
> utility
> and returns 0 for success.

The segfault was wrong, anyway. I applied the patch. This should give  
you some idea how far behind I am on my email, but I just finished my  
second week at the new job and may be reclaiming some sort of semblance  
of normality, so... trying to catch up.

(If wasn't linux-kernel Documentation maintainer and could afford to  
skip that list, this would be easier...)

Rob
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