Re: Symlinks of sh to bash breaks extra args?

Michael Albinus <[email protected]> writes:

> Joel Reicher <[email protected]> writes:
>
>> I've only just started looking at how all this works so I'm 
>> sure there's a lot I don't understand, but it seems to me the 
>> intention of tramp-sh-extra-args is broken by the combination 
>> of it using a regex on bash, the default remote shell for tramp 
>> being /bin/sh, and then the (quite common) arrangement of the 
>> remote having a symlink from /bin/sh to /bin/bash. The result 
>> is then bash, but tramp doesn't know it and then never applies 
>> those extra args.
>
> That is true. When tramp-sh-extra-args was added to Tramp 
> (2002-06-19 according to the ChangeLog), this problem (/bin/sh 
> is a link) didn't exist. And even now, on many remote systems 
> (like my QNAP NAS), the setup is different.
>
> However, I don't know a better way to know which shell variant 
> is used on the remote system prior calling it.
>
>> Is this a problem? I don't know how important those extra args 
>> are, but things seem to work better with them.
>
> Users change tramp-default-remote-shell. And then, there is a 
> good chance to benefit from tramp-sh-extra-args.

And that's kind of what I'm struggling with. I can see the default 
value for extra args caters for both bash and zsh. Let's imagine I 
have both; which one would be a "better Tramp buddy" as you say 
below? And even as a third option I think invoking bash as sh 
enables some POSIX compatibility and disables some bash-specific 
features, so perhaps that's better still?

My problem here is that from what I can tell the remote shell is 
Tramp's agent, and I don't really know what helps Tramp the 
most. In the abstract I'm kind of a bit surprised it doesn't 
deploy a custom command loop with simple semantics implemented as 
an awk script or something like that. (Dependent on a good awk 
being available, of course.)

> The settings are not essential. They give just a set of 
> arguments which help to be a better Tramp buddy. But if they 
> aren't used, the Tramp manual gives you several hints for 
> configuration of the remote shell, mainly based on the value of 
> $TERM.

I do think I understand the options, but as I said above, I'm not 
sure how to figure out what I'm aiming for.

Thanks and regards,

       - Joel