Re: expected behavior of --results with -n0

[Ole Tange]

On Wed, Jul 6, 2016 at 9:30 PM, Joel Uckelman <uckelman@nomic.net> wrote:
> Thus spake Joel Uckelman:
>>
>> When I run this:
>>
>>   seq 3 | parallel --results b -n0 echo hey
>>
>> parallel writes me a directory tree like this:
>>
>>   [uckelman@scylla tmp]$ tree b
>>   b
>>   └── 1
>>       └── \\0
>>           ├── seq
>>           ├── stderr
>>           └── stdout
>
> I think I figured out why this happens---there is only one input
> source (represented by b/1) and there is only one unique value which
> comes from it, i.e., nothing, due to -n0, which gets represented
> as a null escape, \0.

Close. It is of the thought: What is the correct thing to do?

This:

$ seq 4 | parallel -n2 --results a echo

should give:

a/1/1/1/2/seq
a/1/1/1/2/stderr
a/1/1/1/2/stdout
a/1/3/1/4/seq
a/1/3/1/4/stderr
a/1/3/1/4/stdout

because there are 2 values for each command.

And this:

$ seq 2 | parallel -n1 --results a echo

should give:

a/1/1/seq
a/1/1/stderr
a/1/1/stdout
a/1/2/seq
a/1/2/stderr
a/1/2/stdout

because there is 1 value.

So the question is: What is the correct thing to do when there are 0
values? What should this give:

$ parallel -n0 --results a echo ::: a b c ::: 1 2 3

> It looks like what I want instead is this:
>
>   seq 3 | parallel --results b 'echo hey ; true'
>
> Each run gets a unique value from the input, but those arguments are
> all fed to 'true', which safely ignores the arguments it's given.

That would work, however, to keep the correct exit value instead use '|| true'.

seq 3 | parallel --results b 'echo hey || true'


/Ole