Re: [gentoo-catalyst] [PATCH v2 2/2] livecdfs-update.sh: Use `bash --login` to spawn startx

[Matt Turner <mattst88@gentoo.org>]

On Wed, Mar 6, 2013 at 9:02 AM, W. Trevor King <wking@tremily.us> wrote:
> From: "W. Trevor King" <wking@tremily.us>
>
> Starting a "login" version of Bash via `su` is tricky.  The naive:
>
>   su - ${first_user} -c startx
>
> fails because `su - ...` clears a number of environment variables (so
> the prefixed `source /etc/profile` doesn't accomplish anything), but
> Bash isn't started with the `--login` option, so it doesn't source
> /etc/profile internally.  From bash(1):
>
>   A login shell is one whose first character of argument zero is a -,
>   or one started with the --login option.
>   ...
>   An interactive shell is one started without non-option arguments and
>   without the -c option whose standard input and error are both
>   connected to terminals (as determined by isatty(3)), or one started
>   with the -i option...
>   ...
>   When bash is invoked as an interactive login shell, or as a
>   non-interactive shell with the --login option, it first reads and
>   executes commands from the file /etc/profile, if that file exists.
>   After reading that file, it looks for ~/.bash_profile,
>   ~/.bash_login, and ~/.profile, in that order, and reads and executes
>   commands from the first one that exists and is readable.  The
>   --noprofile option may be used when the shell is started to inhibit
>   this behavior.
>
> In order to get the login-style profile loading with a non-interactive
> `su` invocation, you need to use something like:
>
>   echo "${command}" | su - "${user}"
>
> This starts a login shell and pipes the command in via stdin, which
> seems to fake Bash into thinking its running from an interactive
> terminal.  Not the most elegant, but the other implementations I can
> think of are even worse:
>
>   su - "${user}" -c "bash --login -c ${command}"
>   su - "${user}" -c 'source /etc/profile &&
>       (source .bash_profile || ...) && ${command}"
>
> The old expression was broken anyway due to unescaped ampersands in
> the sed expression.  From sed(1):
>
>   s/regexp/replacement/
>     Attempt to match regexp against the pattern space.  If successful,
>     replace that portion matched with replacement.  The replacement
>     may contain the special character & to refer to that portion of
>     the pattern space which matched, and the special escapes \1
>     through \9 to refer to the corresponding matching sub-expressions
>     in the regexp.
>
> This means that the old expression (with unescaped ampersands) lead
> to:
>
>   source /etc/profile ##STARTX##STARTX su - ${first_user} -c startx
>
> with ${first_user} expanded.  This commented out startx, so it was
> never run.
> ---
>  targets/support/livecdfs-update.sh | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/targets/support/livecdfs-update.sh b/targets/support/livecdfs-update.sh
> index 77d694e..0ac41dd 100644
> --- a/targets/support/livecdfs-update.sh
> +++ b/targets/support/livecdfs-update.sh
> @@ -388,9 +388,7 @@ esac
>  # We want the first user to be used when auto-starting X
>  if [ -e /etc/startx ]
>  then
> -       sed -i \
> -               "s:##STARTX:source /etc/profile && su - ${first_user} -c startx:" \
> -               /root/.bashrc
> +       sed -i "s:##STARTX:echo startx | su - '${first_user}':" /root/.bashrc
>  fi
>
>  if [ -e /lib/rcscripts/addons/udev-start.sh ]
> --
> 1.8.2.rc0.16.g20a599e
>
>

This doesn't apply after PATCH 1/2 in this series. Probably why the
first PATCH wasn't labeled as 1/2. Want to confirm what you want to do
here?