Re: The difference between `X=x f | cat` and `{ X=x; f; } | cat`

[Peng Yu]

On 1/19/23, Kerin Millar <kfm@plushkava.net> wrote:
> On Thu, 19 Jan 2023 14:30:50 +0000
> Kerin Millar <kfm@plushkava.net> wrote:
>
>> On Thu, 19 Jan 2023 08:02:07 -0600
>> Peng Yu <pengyu.ut@gmail.com> wrote:
>>
>> > Hi,
>> >
>> > f is a function that uses a variable called X, which is not declared in
>> > f.
>> >
>> > As far as I can tell, the following two ways produce the same results.
>> >
>> > - `X=x f | cat`
>> > - `{ X=x; f; } | cat`
>>
>> They are not equivalent.
>>
>> $ bash -c 'f() { declare -p X; }; X=x f; declare -p X'
>> declare -x X="x"
>> bash: line 1: declare: X: not found
>>
>> $ bash -c 'f() { declare -p X; }; X=x; f; declare -p X'
>> declare -- X="x"
>> declare -- X="x"
>>
>> The first version defines X in such a way that it affects only the
>> operating environment in which f is run. Note, also, that the variable is
>> marked as being exportable, meaning that it would be present in the
>> environment of any subprocesses that might be launched by f. For a more
>> rigorous explanation, refer to the SIMPLE COMMAND EXPANSION section of the
>> manual.
>
> Here, I forgot to say that, in the case that f is an executable, X will also
> be present in the environment of that particular subprocess. Whether it is
> present in the environment of any subprocesses in turn would depend on
> whether f decides to propagate the environment as it was originally
> inherited.

Thanks. But my question is about f being a bash function. I don't care
when f is not a function. I know X will be defined in the environment
in the latter case, whether f is a function or not.

-- 
Regards,
Peng