Re: any plans for command substitution that preserves trailing newlines?

[Chet Ramey]

On 6/1/21 5:03 PM, Christoph Anton Mitterer wrote:
> On Tue, 2021-06-01 at 09:26 -0400, Chet Ramey wrote:
> > > I wondered whether there were any plans to implement proper support
> > > for
> > > command substitutions that preserves trailing newlines?
> >
> > "Proper" is doing a lot of work in ths sentence.
>
> What do you mean? That would be much work to get it implemented in the
> shell?

I interpreted it to mean "appropriate" or "necessary." I don't think it's
either of those things.


> > That implies it's something that people want to standardize. I
> > haven't
> > seen any evidence of that.
>
> And there is no guarantee it would ever happen. But at least with e.g.
> $'...' strings it seems to work and POSIX might sooner or later
> standardise it.

Maybe. I'm just skeptical of its value, given that ways to accomplish the
task already exist.

> I just though it's a better chance to get it standardised if
> implementations already have something like it - and not the other way
> round.

That's certainly true.

> > Why is inventing new syntax the right approach?
>
> I guess no normal developer writing shell scripts will typically use
> these workarounds. It's not even easy to spot all the places where it
> would be needed.

So we should invent something new because nobody will use the existing
methods? Why would they change to use a new method, if they can't spot
the places where it's needed now?

> Even if, it's quite impractical to constantly change LC_ALL or read the
> value via IFS='' read -rd '' var < <(cmd).

As opposed to changing scripts to use some syntax that doesn't yet exist?


> Just imagine a script should delete a file, the path is e.g. previously
> normalised with realpath or maybe one just gets the basename first.
>
> If the file had a trailing newlines in it names the best that can
> happen is that the rm simply fails - or in the worst case another file
> of the same name (but without the trailing newlines) is taken.

If files with trailing newlines are common in your environment, wouldn't
you think that scripts to accommodate them would already use one of the
existing methods?

--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/