bug#54625: Why do I need to specify `-o auto` for join's `-e` option to work?

[Pádraig Brady]

On 29/03/2022 09:07, Iago-lito wrote:
> Hello,
>
>       This is a follow-up to this (yet) unanswered post on SE U&L:
> https://unix.stackexchange.com/q/696259/87656, which I'm cross-posting
> here. Don't hesitate to fire if it's the wrong place.
>
> With the following two simple files:
>
> |a.txt|
>
> |1 a 2 b 5 c |
>
> |b.txt|
>
> |2 x 4 y 5 z |
>
> The following command does not behave like expected:
>
> |$ join -a 1 -a 2 -e 0 a.txt b.txt 1 a 2 b x 4 y 5 c z |
>
> I would expect the option |-e 0| to fill up missing values with zeroes.
> However, the following does work:
>
> |$ join -a 1 -a 2 -e 0 -o auto a.txt b.txt 1 a 0 2 b x 4 0 y 5 c z |
>
> Reading documentation from |$ man join|, I see no connection between
> |-o| and |-e| that would make the above behaviour meaningful. Instead, I
> find it misleading that a useless |-o auto| needs to be inserted into my
> command for |-e 0| to work..
>
> Is there an explanation, to be clarified in the manpage? Or is it a bug?


The info doc is clearer that the output of missing fields need to be
explicitly enabled, https://www.gnu.org/software/coreutils/join :

  ‘-e STRING’
     Replace those output fields that are missing in the input with
     STRING.  I.e., missing fields specified with the ‘-12jo’ options.
I agree that the man page should mention this also,
which I've done in the attached.

Marking this as done.
thanks,
Pádraig

join-e-usage.patch
Description: Text Data