set temporary environment variables for builtins

set temporary environment variables for builtins

[Clinton Bunch]

I was playing around with date formats using print -P and tried to get 
the time in Paris.

This didn't work:

TZ=Europe/Paris print -P '%D{%Y%m%dT%H%M%S%z}'

This does:

export TZ=Europe/Paris

print -P '%D{%Y%m%dT%H%M%S%z}'


but I have to unset/restore TZ afterwards.


I also tried:

() { typeset -x TZ=Europe/Paris; print -P '%D{%Y%m%dT%H%M%S%z}' }

It left me with TZ set.

I know this can be done with the date command, but it's one of those 
things that went from "Let's try this" to "Surely, there's a way to do this"

Is this a bug or design decision?

echo $ZSH_VERSION $ZSH_PATCHLEVEL $OSTYPE
5.8 zsh-5.8-0-g77d203f linux-gnu

cat /etc/system-release
Rocky Linux release 9.3 (Blue Onyx)

Re: set temporary environment variables for builtins

[Lawrence Velázquez]

On Sat, Dec 16, 2023, at 12:59 PM, Clinton Bunch wrote:
> I also tried:
>
> () { typeset -x TZ=Europe/Paris; print -P '%D{%Y%m%dT%H%M%S%z}' }
>
> It left me with TZ set.

With GLOBAL_EXPORT enabled (which is the default), ''typeset -x''
acts like ''typeset -gx''.  Use ''local -x''.

	% typeset -p TZ
	typeset: no such variable: TZ
	% () { local -x TZ=Europe/Paris; print -P '%D{%z}' }
	+0100
	% typeset -p TZ
	typeset: no such variable: TZ

-- 
vq

Re: set temporary environment variables for builtins

[Clinton Bunch]

Thanks.  That worked.

Still wondering why the standard syntax for setting a temporary 
environment variable doesn't work for builtins.

I don't think I'm unusual in expecting this to work:

TZ=Europe/Paris print -P '%D{%z}'

Granted this is much more likely something someone would use with TZ=UTC.

On 12/16/2023 12:53 PM, Lawrence Velázquez wrote:
> On Sat, Dec 16, 2023, at 12:59 PM, Clinton Bunch wrote:
>> I also tried:
>>
>> () { typeset -x TZ=Europe/Paris; print -P '%D{%Y%m%dT%H%M%S%z}' }
>>
>> It left me with TZ set.
> With GLOBAL_EXPORT enabled (which is the default), ''typeset -x''
> acts like ''typeset -gx''.  Use ''local -x''.
>
> 	% typeset -p TZ
> 	typeset: no such variable: TZ
> 	% () { local -x TZ=Europe/Paris; print -P '%D{%z}' }
> 	+0100
> 	% typeset -p TZ
> 	typeset: no such variable: TZ
>

Re: set temporary environment variables for builtins

[Bart Schaefer]

On Sat, Dec 16, 2023 at 11:48 AM Clinton Bunch <cdb_zsh@zentaur.org> wrote:
>
> Still wondering why the standard syntax for setting a temporary
> environment variable doesn't work for builtins.
>
> I don't think I'm unusual in expecting this to work:

https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_09_01
(2.9.1 Simple Commands)

"If the command name is not a special built-in utility or function,
the variable assignments shall be exported for the execution
environment of the command and
  (my emphasis) shall not affect the current execution environment
except as a side-effect of the expansions performed in step 4"

"print" is not a "special" built-in, so "shall not affect" applies.  "Step 4" is

"Each variable assignment shall be expanded for tilde expansion,
parameter expansion, command substitution, arithmetic expansion, and
quote removal prior to assigning the value."

Re: set temporary environment variables for builtins

[Lawrence Velázquez]

On Sat, Dec 16, 2023, at 2:48 PM, Clinton Bunch wrote:
> Still wondering why the standard syntax for setting a temporary 
> environment variable doesn't work for builtins.

It does work, in general.

	% print -P '%D{%B}'
	December
	% LC_TIME=fr_FR.UTF-8 print -P '%D{%B}'
	décembre
	% print -r -- $LC_TIME

	%

> I don't think I'm unusual in expecting this to work:
>
> TZ=Europe/Paris print -P '%D{%z}'

The issue might be unique to TZ or TZ + print, but I'll defer to
someone who actually has a clue (or has time to unearth one).

-- 
vq

Re: set temporary environment variables for builtins

[Bart Schaefer]

On Sat, Dec 16, 2023 at 12:22 PM Lawrence Velázquez <larryv@zsh.org> wrote:
>
> It does work, in general.

Well, no, it doesn't.  It works for parameters that zsh separately
considers to be "special", which includes all the LC_* variants.  TZ
is not special.

Re: set temporary environment variables for builtins

[Roman Perepelitsa]

On Sat, Dec 16, 2023 at 9:28 PM Bart Schaefer <schaefer@brasslantern.com> wrote:
>
> On Sat, Dec 16, 2023 at 12:22 PM Lawrence Velázquez <larryv@zsh.org> wrote:
> >
> > It does work, in general.
>
> Well, no, it doesn't.  It works for parameters that zsh separately
> considers to be "special", which includes all the LC_* variants.  TZ
> is not special.

In which sense is LC_TIME special for print but TZ is not?

Roman.

Re: set temporary environment variables for builtins

[Bart Schaefer]

On Sat, Dec 16, 2023 at 12:32 PM Roman Perepelitsa
<roman.perepelitsa@gmail.com> wrote:
>
> In which sense is LC_TIME special for print but TZ is not?

In the sense that LC_* are always special, as noted by the <S>
notation in "man zshparam".

Re: set temporary environment variables for builtins

[Mikael Magnusson]

On 12/16/23, Roman Perepelitsa <roman.perepelitsa@gmail.com> wrote:
> On Sat, Dec 16, 2023 at 9:28 PM Bart Schaefer <schaefer@brasslantern.com>
> wrote:
>>
>> On Sat, Dec 16, 2023 at 12:22 PM Lawrence Velázquez <larryv@zsh.org>
>> wrote:
>> >
>> > It does work, in general.
>>
>> Well, no, it doesn't.  It works for parameters that zsh separately
>> considers to be "special", which includes all the LC_* variants.  TZ
>> is not special.
>
> In which sense is LC_TIME special for print but TZ is not?

Setting any of the LC_* parameters explicitly calls some locale stuff
(whether or not it is exported), apart from just setting the
parameters:

/**/
void
lcsetfn(Param pm, char *x)
{
    char *x2;
    struct localename *ln;

    strsetfn(pm, x);
    if ((x2 = getsparam("LC_ALL")) && *x2)
	return;
    queue_signals();
    /* Treat empty LC_* the same as unset. */
    if (!x || !*x)
	x = getsparam("LANG");

    /*
     * If we've got no non-empty string at this
     * point (after checking $LANG, too),
     * we shouldn't bother setting anything.
     */
    if (x && *x) {
	for (ln = lc_names; ln->name; ln++)
	    if (!strcmp(ln->name, pm->node.nam))
		setlocale(ln->category, unmeta(x));
    }
    unqueue_signals();
    clear_mbstate();	/* LC_CTYPE may have changed */
    inittyptab();
}


-- 
Mikael Magnusson

Re: set temporary environment variables for builtins

[Lawrence Velázquez]

On Sat, Dec 16, 2023, at 3:27 PM, Bart Schaefer wrote:
> On Sat, Dec 16, 2023 at 12:22 PM Lawrence Velázquez <larryv@zsh.org> wrote:
>>
>> It does work, in general.
>
> Well, no, it doesn't.  It works for parameters that zsh separately
> considers to be "special", which includes all the LC_* variants.  TZ
> is not special.

Huh, this is very surprising to me.  I guess I never noticed because
almost all the variables that can influence builtins (e.g., CDPATH,
LC_*, OPTIND, etc.) are special.

-- 
vq

Re: set temporary environment variables for builtins

[Roman Perepelitsa]

On Sun, Dec 17, 2023 at 1:27 AM Lawrence Velázquez <larryv@zsh.org> wrote:
>
> On Sat, Dec 16, 2023, at 3:27 PM, Bart Schaefer wrote:
> > On Sat, Dec 16, 2023 at 12:22 PM Lawrence Velázquez <larryv@zsh.org> wrote:
> >>
> >> It does work, in general.
> >
> > Well, no, it doesn't.  It works for parameters that zsh separately
> > considers to be "special", which includes all the LC_* variants.  TZ
> > is not special.
>
> Huh, this is very surprising to me.  I guess I never noticed because
> almost all the variables that can influence builtins (e.g., CDPATH,
> LC_*, OPTIND, etc.) are special.

I am also surprised by this. It does make sense given the
implementation details but it's not how I expected zsh to behave.

Would it make sense to make all parameters that affect builtins
special? Are there parameters other than TZ that affect builtins but
aren't already special?

Roman.