[tz] strftime %s

[Guy Harris]

On Jan 12, 2024, at 11:47 AM, Steve Summit via tz <tz at iana.org> wrote:

> But, despite their non-human-readableness, time_t values are now
> so ubiquitous that they are occasionally of interest to humans,
> so at some point along the way, the 'date' command acquired "%s"
> as one of its custom output format specifiers.

At some point, *somebody's* "date" command may have acquired "%s", but it's not in issue 7 of POSIX/SUS.

> I gather from this thread that someone has decided to "solve"
> this problem anyway, by officially adding %s to the supported
> strftime formats.  However, it seems to me that the only
> "problem" here is that the 'date' program has been difficult to
> write.  My own opinion is that dragging the whole rest of the
> world through this mudpit is not the right way of solving date's
> implementation problem -- but then, I'm not on the Posix
> committee, so it doesn't matter what I think.

From looking at the POSIX 8 draft, %s was added to strftime() as a result of Austin Group Defect 169.

That defect noted that there's no POSIX-compliant way to, in a shell script, get a string that's the numerical value of the current time_t, and requested a "%s" output format identifier for the date command, rather than, say, a "-e" (for "Epoch") command-line flag.

The result of the discussion for that defect was that %s should be added to strftime().