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Re: are posix-shell-compliant continuation lines valid/supported, or not

From: Mike Gilbert
Subject: Re: are posix-shell-compliant continuation lines valid/supported, or not, in /etc/default/grub ?
Date: Thu, 19 Mar 2020 20:51:17 -0400

On Thu, Mar 19, 2020 at 5:19 PM PGNet Dev <address@hidden> wrote:
> a recent grub package update, in ubuntu 18LTS, is breaking /etc/default/grub 
> by mangling/overwriting users' entries, in the specific case of using 
> continuation lines in the file/config. and, subsequently, the upgrade process 
> on these servers.

This sounds like an issue you should hash out with your distro
maintainer. How Ubuntu manages package upgrades is not within the
scope of this mailing list.

> it'd be useful/helpful to get clear on what the 'official' grub project 
> support for use of posix-shell-compliant continuation lines is ...
> are they 'supported' as valid use in /etc/default/grub, or not?

The manual section you quoted seems pretty clear to me: it must be
valid POSIX shell input. Backslash-escaped newlines are valid POSIX
shell input.

Technically speaking, /etc/default/grub is sourced by grub-mkconfig,
which is executed by /bin/sh. So long as /bin/sh is able to correctly
process both grub-mkconfig and /etc/default/grub, you probably wont
have a problem. If /bin/sh happens to be bash, you could probably get
away with putting bash-specific code in /etc/default/grub if you
really wanted to.

What your distro chooses to support is really up to them, however.

> also useful to know/understand whether any grub update can/should mangle a 
> user's /etc/default/grub.  allowed? expected?

I think this is not something the grub developers care about; work it
out with your distro maintainer.

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