[Nix-dev] Dealing with non-Bash /bin/sh on non-NixOS

[Eelco Dolstra]

Hi Peter,

On 09/11/12 18:57, Peter Simons wrote:

>  >> we should link /bin/sh to Dash instead of Bash. That would catch any
>  >> implicit dependencies on non-POSIX shell features,
>  >
>  > What's the point of that? Breaking zillions of existing scripts for
>  > very little gain doesn't sound like a good idea to me.
> 
> now I am confused. In the very posting I was responding to, you said:
> 
>  | Yes, fix builders not to rely on /bin/sh (or at least not to assume
>  | it's Bash).
> 
> Apparently, we consider builders broken that assume /bin/sh to be Bash.
> So why don't you see the benefit of using a non-Bash shell for /bin/sh
> to expose those broken builders?

What I meant was that in Nixpkgs you shouldn't assume that /bin/sh is Bash,
because we obviously don't control that on non-NixOS systems.  So builders
should *not* use /bin/sh, but ${pkgs.bash}/bin/sh (or whatever shell they want),
i.e. make the shell dependency explicit.  And then there is no problem in using
shell-specific features.

Ideally we wouldn't have /bin/sh in Nix chroots, but that's not realistic given
that functions like system() require /bin/sh.

> Besides, everyone who is running Nix on a host system other than NixOS
> potentially *has* a non-Bash /bin/sh. (Which is why this thread was
> started.) So it doesn't feel right to say that changing /bin/sh to a
> non-Bash shell would "break scripts". That change would just expose
> scripts that are broken already.

No, that's completely wrong.  Backwards compatibility is important, much more
than POSIX compatibility: you can't just quietly change /bin/sh and then say
that those scripts were "already broken".  They worked just fine :-)

-- 
Eelco Dolstra | LogicBlox, Inc. | http://nixos.org/~eelco/