[U-Boot] 'filesize' env var - making U-Boot command more scriptable?

[Wolfgang Denk]

Dear Tim,

In message <CAJ+vNU1c86fd3yj+qnZE5SnPLmzHaUWF68oT+gwHKYmNag84Hg at mail.gmail.com> you wrote:
> 
> Various U-Boot commands that deal with files/blobs end up setting the
> 'filesize' env variable to be used for subsequent commands which is
> very handy. I haven't found this documented anywhere but a scan of the
> code looks like this is done by

Documentation is certainly not perfect, but at least filesize gets
mentioned in the U-Boot environment variables section of the manual;
see the very end of [1] (plus a few othe rplaces).

[1] http://www.denx.de/wiki/view/DULG/UBootEnvVariables



> I've seen other commands that allow a usage that will allow specifying
> a var name to put a result in.
> 
> I've noticed commands such as 'ubi' and 'nand' would benefit from
> setting filesize when dealing with volume names and partition names.
> I've also noticed how some commands (ie nand) are good about reporting
> sizes in hex but others (ie ubi) report them in decimal only making it
> difficult for someone to even cut-and-paste sizes to following
> commands.
> 
> Has there been a desire or proposal to make this more standard or come
> up with something different?

If you really think about it, all of this is just a worarounf for
the lack of command substitution (aka backquotes / backticks) in the
available command interpreters in U-Boot.

The currently most used one is based on an ancient version of hush
from the BusyBox project.  It has a large number of severe
restrictions and a fair number of known other issues.

IMO if somebody is willing to spend efforts in this area it would be
best to replace hust by a more recent version of a shell, adding
command substitution.

[If you go a step further you might even think about introducing a
concept of "files" and adding pipes.  But then we would be mioving
more and more into the direction of an OS ;-) ]

Best regards,

Wolfgang Denk

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