[U-Boot] U-boot env variables parsing

[Joakim Tjernlund]

Wolfgang Denk <wd at denx.de> wrote on 2010-04-01 20:27:47:
>
> Dear Joakim Tjernlund,
>
> In message <OF5552925C.8F998468-ONC12576F8.005E3247-C12576F8.
> 005E9BF2 at transmode.se> you wrote:
> >
> > > To me it looks like the new code would indeed do a "greedy" substitution
> > > only stopping when no more substitutions can be done.  This is very
> > > un-unixy and thus not something I'd like to see as a default behaviour.
> >
> > Why not? What is gained by the current method?
>
> We follow the principle of least surprise [1]; the command line
> interpeter in U-Boot should behave as similar to a (say, POSIX
> compatible) shell as possible. Restrictions and deviations are not
> intentional, but caused by the attempt to do with a minimal memory
> footprint.
>
> Like Detlev I feel/fear that the suggested change will cause more
> annoyance due to unexpected behaviour that it will do good.

what bad do you think it might do? You mentioned the possibility
to pass arg=$(name) literally(why would you do that?)
Have you ever done that? Then one should be able to
pass $(linuxip) too, which you can't.

>
>
> I also see little actual need for such an extension, as in all cases
> I've seen so far it has been possible to acchieve the goal without
> code changes by just minimal adjustments of the definitions. For
> example, your code:
>
> linuxip=ip=$(ipaddr)::$(gatewayip):$(netmask):$(hostname):$(linuxif):off
> tboot=setenv bootargs $(linuxroot) $(linuxip) $(extra);tftp 100000; bootm 100000
>
> could be rewritten from plain variable definitions into an equivalent
> command sequence, like that:
>
> setenv setip 'setenv bootargs ${bootargs} ip=${ipaddr}::${gatewayip}:$
> {netmask}:${hostname}:${linuxif}:off'
>
> Do the same for "linuxroot" (=> setroot) and "extra" (=> setextra),
> and then use:
>
> setenv tboot 'run setroot setip setextra;tftp 100000;bootm'
>
> will do exactly what you want. Detlev quoted similar code earlier.
> This is what many, many existing boards use, and what we explain in
> great detail in the manual.

While you can do that, it is ugly and clumsy(which was why I wrote the patch)

I want the shell to make things simpler/easier for me and the above
isn't either.

 Jocke