[U-Boot] [PATCH V2 4/4] cmd_part: add partition-related command

[Stephen Warren <swarren@wwwdotorg.org>]

On 09/06/2012 11:12 AM, Tom Rini wrote:
> On Wed, Sep 05, 2012 at 08:38:26PM -0600, Stephen Warren wrote:
>> On 09/05/2012 05:51 PM, Rob Herring wrote:
>>> On 09/05/2012 05:03 PM, Stephen Warren wrote:
>>>> From: Stephen Warren <swarren@nvidia.com>
>>>>
>>>> This implements the following:
>>>>
>>>> part uuid mmc 0:1
>>>>   -> print partition UUID
>>>> part uuid mmc 0:1 uuid
>>>>   -> set environment variable to partition UUID
>>>
>>> What's the reason to not always both print out and set the uuid env var?
>>>
>>> Perhaps the env name should be partuuid or part_uuid as you could have
>>> uuid's for other purposes?
>>
>> The idea is that if you're running the command interactively, you won't
>> pass a variable name on the command-line, so the command will print out
>> the UUID for you to read. In this case, it's pointless to set any
>> environment variable.
>>
>> However, if you're writing a script, you want to capture the UUID into
>> an environment variable, and it's quite unlikely you want to litter
>> stdout with that content too. Hence, either-or, not both.
> 
> Do other commands have a "I'm being scripted, probably, don't stdout"
> and "I'm being interactive, use stdout" distinction like this?  IMHO,
> always printing out makes sense so you can "see" that your script is
> working as you expect.

In general, as a script writer, yes you do have the ability to choose.
Typically, I'd write:

part uuid ....

vs.

var=`part uuid ....`

in order to control this. However, U-Boot's shell doesn't support
backticks. As a script writer, I certainly desire the ability to control
what commands spam to the console, and really don't think it's useful to
print the UUID from a script (does the user really care, and any script
developer can just echo it for debugging if they need it).

I'm not aware of other U-Boot commands whose purpose it is to set
environment variables, so can't really compare.

Still, if you're insistent on this point, I can change the code to
always print, and optionally write an environment variable.