Re: [PATCH v2 0/2] env: setenv add resolve value option
On Sat, Nov 20, 2021 at 8:36 PM Wolfgang Denk wd@denx.de wrote:
Dear Artem,
In message CAKaHn9KZg13r=pGCo=Lv69pBP-s-EW4uxjBVuH9veT+o5j9v+g@mail.gmail.com you wrote:
next examples just demonstrate how its works for already defined env variables which contain other variables (like storred env variables)
Which next examples?
Usage examples (from commit message):
=> setenv a hello; setenv b world; setenv c '${a} ${b}' => setenv -r d '${c}! ${a}...' => printenv d d=hello world! hello...
sure I know about this ! see my prev message please .
Which exact message are you referring to here?
Why not have this new opportunity ?
I think the suggested code is adding more problems than it solves.
have in mind, as you speak of "deep resolve". But then, I'm first missing an explanation (and documentation) of what "deep resolve"
recurrent resolving for variables
Your implementation of recursion has an arbiotrary and undocumented depth limit. Also, I cannot see a way to prevent resolving in case I want to keep something like "$foo" in the result.
But that's to be expected from such a non-standard way.
Why don't you stick with what "eval" in a standard shell does?
actually means in this context, i. e. how many levels down you evaluat. Oh... the code has "int max_loop = 32;" - this is a
i think its will be enough
It is a reallybad habt to implement code with arbitrary limits, as it will blow into your face (or more likely that of an innocent user) rather sooner than later. It's even worse that this limit is nowhere documented.
- this option did not broke any exist compatibilities
- there we talk not only about uboot shell, same time will be useful
to have env_resolve for internal c usage, because env_set dont have this feature
I did not say that an "eval" like construct would not be useful. But uncontrolled recursion with an undocumented depth limit is a problem.
yes i'm informed about this plans (and think its happens not so soon - but i provide some simple elegant solution already) but again we dont have env_resolve for internal c usage which must be very useful
On the CLI, we use the "run" command to get the desired effect. Yes, this is neither perfect nor elegant. But you can use that in C code as well.
will be easy get useful features via simple solution ( deep resolve all vars by one line )
I understand what you want, but this is not a good way to solve the problem. I'd really rather see such efforts invested in helping Francis with the hush update - which will make such code unnecessary.
Best regards,
Wolfgang Denk
-- DENX Software Engineering GmbH, Managing Director: Wolfgang Denk HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@denx.de Success in marriage is not so much finding the right person as it is being the right person.
Dear Artem,
In message CAKaHn9+yL3naiDqbsQJWQ0Po=g=TmjjcPSKxkx5C4ay1M1AsUA@mail.gmail.com you wrote:
next examples just demonstrate how its works for already defined env variables which contain other variables (like storred env variables)
Which next examples?
Usage examples (from commit message):
=> setenv a hello; setenv b world; setenv c '${a} ${b}' => setenv -r d '${c}! ${a}...' => printenv d d=hello world! hello...
This is a very simple example, and I showed you how you can solve this one by just omitting the apostrophes:
=> setenv a hello; setenv b world; setenv c ${a} ${b} => setenv d ${c}! ${a}... => printenv d d=hello world! hello...
I _think_ what you actually have in mind is something like this:
=> setenv a hello => setenv b world => setenv c '${a} ${b}' => setenv a goodbye => setenv b sunshine
something to set d to: '${c}! ${a}...'
=> printenv d
Here my simple approach does not show what you want to have:
=> setenv a hello => setenv b world => setenv c ${a} ${b} => setenv a goodbye => setenv b sunshine => setenv d ${c}! ${a}... => printenv d d=hello world! goodbye...
That's because here evaluation takes place at assignment, but you want it when used - but being recursive here is neither a good idea nor standard.
How would you do it in a standard posix shell? You would have to use "eval", like that:
$ a=hello $ b=world $ c='${a} ${b}' $ a=goodbye $ b=sunshine $ d=$(eval echo $c) $ echo $d goodbye sunshine
But please note that "eval" is _not_ recursive!!
$ a='$b' $ eval echo $c $b sunshine
And this is why I object against this patch.
Oh, and in U-Boot you could write this as:
=> setenv a hello => setenv b world => setenv c '${a} ${b}' => setenv a goodbye => setenv b sunshine => setenv foo "setenv d ${c}! ${a}..." => run foo => printenv d d=goodbye sunshine! goodbye...
And yes, here you have to be careful about using ' or " as there is no recursion like you might expect.
So yes, it would be nice if we had "eval" (which will ocme with the hush update), and no, "eval" does not recurse either.
Best regards,
Wolfgang Denk
On Mon, Nov 22, 2021 at 4:52 PM Wolfgang Denk wd@denx.de wrote:
Dear Artem,
In message CAKaHn9+yL3naiDqbsQJWQ0Po=g=TmjjcPSKxkx5C4ay1M1AsUA@mail.gmail.com you wrote:
next examples just demonstrate how its works for already defined env variables which contain other variables (like storred env variables)
Which next examples?
Usage examples (from commit message):
=> setenv a hello; setenv b world; setenv c '${a} ${b}' => setenv -r d '${c}! ${a}...' => printenv d d=hello world! hello...
This is a very simple example, and I showed you how you can solve this one by just omitting the apostrophes:
=> setenv a hello; setenv b world; setenv c ${a} ${b} => setenv d ${c}! ${a}... => printenv d d=hello world! hello...
sure i know it and its easy, but we still have some misunderstanding, and i will try explain again our problem
our problem (TASK)
we have: some env variables which already defined and we totally dont know about content ( for example its was improved by `env import` or loaded from env storage and "setenv a hello; setenv b world; setenv c '${a} ${b}'; setenv d '${c}! ${a}...' ;" just example how emulate this env state )
we need: setup/resolve env variable for example from d (and need resolve all sub included vars) => setenv -r e $d => printenv e => e=hello world! hello...
please explain how we can get it without -r (deep resolve option) via standard way ?
I _think_ what you actually have in mind is something like this:
=> setenv a hello => setenv b world => setenv c '${a} ${b}' => setenv a goodbye => setenv b sunshine
something to set d to: '${c}! ${a}...'
=> printenv d
Here my simple approach does not show what you want to have:
=> setenv a hello => setenv b world => setenv c ${a} ${b} => setenv a goodbye => setenv b sunshine => setenv d ${c}! ${a}... => printenv d d=hello world! goodbye...
That's because here evaluation takes place at assignment, but you want it when used - but being recursive here is neither a good idea nor standard.
How would you do it in a standard posix shell? You would have to use "eval", like that:
$ a=hello $ b=world $ c='${a} ${b}' $ a=goodbye $ b=sunshine $ d=$(eval echo $c) $ echo $d goodbye sunshine
But please note that "eval" is _not_ recursive!!
$ a='$b' $ eval echo $c $b sunshine
And this is why I object against this patch.
Oh, and in U-Boot you could write this as:
=> setenv a hello => setenv b world => setenv c '${a} ${b}' => setenv a goodbye => setenv b sunshine => setenv foo "setenv d ${c}! ${a}..." => run foo => printenv d d=goodbye sunshine! goodbye...
And yes, here you have to be careful about using ' or " as there is no recursion like you might expect.
So yes, it would be nice if we had "eval" (which will ocme with the hush update), and no, "eval" does not recurse either.
Best regards,
Wolfgang Denk
-- DENX Software Engineering GmbH, Managing Director: Wolfgang Denk HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@denx.de Real computer scientists despise the idea of actual hardware. Hard- ware has limitations, software doesn't. It's a real shame that Turing machines are so poor at I/O.
participants (2)
-
Art Nikpal -
Wolfgang Denk