[Bug 218711] strftime man page incorrectly claims that TZ is used

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=218711

--- Comment #1 from Alejandro Colomar (alx@kernel.org) ---
On Thu, Apr 11, 2024 at 07:44:43PM +0000, bugzilla-daemon@kernel.org wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=218711
> 
>             Bug ID: 218711
>            Summary: strftime man page incorrectly claims that TZ is used
>            Product: Documentation
>            Version: unspecified
>           Hardware: All
>                 OS: Linux
>             Status: NEW
>           Severity: normal
>           Priority: P3
>          Component: man-pages
>           Assignee: documentation_man-pages@kernel-bugs.osdl.org
>           Reporter: gharris@sonic.net
>         Regression: No
> 
> The strftime man page says, in the ENVIRONMENT section, that "The environment
> variables TZ and LC_TIME are used."
> 
> strftime(), in Linux, does not use the TZ environment variable.  It is passed
> a
> pointer to a struct tm, which contains a time stamp that can reflect either
> local time or UTC, and formats a string based on the values in that
> structure. 
> If the structure reflects local time, there is no need for any conversion of
> POSIX time to local time, so TZ is not used.  If the structure reflects UTC,
> the string will reflect UTC, meaning that, again, there is no need for any
> conversion to local time, so TZ is not used.
> 
> TZ is *indirectly* used, because, to quote the Single UNIX Specification page
> for strftime(), "Local timezone information is used as though strftime()
> called
> tzset().", and, to quote the Single UNIX Specification page for tzset(), "The
> tzset() function shall use the value of the environment variable TZ to set
> time
> conversion information used by ctime, localtime, mktime, and strftime."
> 
> The reason why strftime is mentioned is that the %Z format specifier is
> "Replaced by the timezone name or abbreviation, or by no bytes if no timezone
> information exists."  In systems in which struct tm includes the tm_zone
> member, %Z can use the tm_zone member as the timezone abbreviation, but, in
> systems where it does *not* include the tm_zone member, strftime() might, for
> example, have to fall back on using the tzname[] array and the tm_isdst
> member
> to select an element of that array.

Hi Guy,

Would you mind sending a patch to the mailing list, according to the
guidelines?

<https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING>.
<https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING.d/mail>
<https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING.d/patches>

It would be wise to CC Paul Eggert <eggert@cs.ucla.edu>.

Have a lovely day!
Alex

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