[U-Boot] How can I save U-Boot env vars to HUSH shell vars.

[James Chargin <jimccrown@gmail.com>]

Dear Wolfgang,

Thank you for your reply.

On 04/09/2014 02:50 PM, Wolfgang Denk wrote:
> Dear James,
>
> In message <5345B6EC.6050109@gmail.com> you wrote:
>> I'd like to store the values of environment variables in HUSH shell
>> variables and then restore them later. My ultimate goal is to preserve a
>> few environment variables through a "env default -f".
>
> It is probably easier to use "env export" to store this set of
> variables to some area in memory.  You could even make this permanent
> by writing it to flash or some storage device.

I hadn't thought of exporting the environment to memory, excellent idea.

>
>> I'm working with U-Boot 2010.12. Changing to a newer version is not
>> possible at this time.
>
> Heh.  As soon as you have to change _any_ code, you can as well
> upgrade.

I was hoping (in vain perhaps) to do my work modifying only the environment.

>
>> I realize this is a very old U-Boot. I'm hoping that the relevant parts
>> of U-Boot have not changed between that old version and versions you
>> might provide help for.
>
> Well, a ton of bug fixes and improvements have been added since.  One
> of the extensions you want and which has been added only after
> v2010.12 is the capability to export only a sub-set of the environment
> (i. e. a list of variables passed on the command line).
>

This is a definite drawback to having an old U-Boot; I'm sure I would 
benefit from the bug fixes and other enhancements.

Exporting a list of values sounds like a nice addition that would be 
helpful to me.

>> => for i in $e; do v_$i=$i; done
> ...
>> What I get:
>
> ...is exactly what you coded.  You would get the same in any other
> shell, too.
>
>> => showvar
>> HUSH_VERSION=0.01
>> v_e=e ethaddr ipaddr rootpath
>> v_ethaddr=00:00:17:88:09:36
>> v_ipaddr=10.3.134.80
>> v_rootpath=/home/anyuser/a/device/tr/rootfs
>> =>
>>
>> So, how do I re-write the for loop to get the desired results
>
> This would require an "eval" or command substitution, which we do not
> have in our implementation of the hush shell.
>

"eval" seemed to me also to be what I wanted. I'm aware it isn't present 
in hush, but I was hoping for some magic from the community. :-)

> To me it seems the easiest way to get what you want is to use
> "env export ... ethaddr ipaddr rootpath" or similar.
>

I suppose, with my 2010.12, I could export everything to memory and then 
parse through it to find the values I need then import them. Sounds 
vaguely possible but it's probably more complex than doing the U-Boot 
upgrade.

> Um... yes, this requires an update to more recent code.

Yes, update is on my to-do list, but schedules dictate that the upgrade 
is not my first priority. The conclusion reached here adds to the 
argument for doing it sooner rather than later.

>
> Best regards,
>
> Wolfgang Denk
>

Thank you again for you comments.
Jim