Re: date: new options to parse input date with strptime(3)

[Assaf Gordon]

Hello,

Thank you for the review.
(replying to both emails together)

On Wed, Jul 31, 2019 at 04:27:20PM +0100, Stephane Chazelas wrote:
> 2019-07-31 14:59:42 +0100, Pádraig Brady:
> > On 26/07/19 08:29, Assaf Gordon wrote:
> [...]
> > > The first patch adds '--date-format=FORMAT', where FORMAT is
> > > strptime(3) format.
> > 
> > I like this, and think it's useful functionality.
> > It's equivalent to -f in date(1) on FreeBSD,
> > so we should probably support that short option
> [...]
> 
> Note that busybox date has -D for that.

In gnu date(1), -f is already assigned to "--file" (batch processing).
I added the "-D" short option.

> [...] you can use the standard getdate() DATEMSK variable [...]

Based on past coreutils policies, I think new environment variables
won't be accepted to any program...

>> The second patch adds '--arith-format=FORMAT', where FORMAT is
>> limited
>> to years/months/days/hours/minutes/seconds (%Y/%m/%d/%H/%M/%S).
> 
> The idea here is to support more generic numeric deltas.
> I'm not sure of the interface though. Perhaps --delta-format
> would be clearer.

I changed it to "--date-delta-format" (to match -D/--date-format).

Note that there's a difference between this and freebsd's -v:
The "--date-delta-format" takes the values from the same date string
(-d), so it also works with "--file" (batch processing).

> Or perhaps we should just support the
> FreeBSD -v option to apply the adjustments, which seems more direct
> and would further improve compat.

I like the FreeBSD -v method, and implemented it as well (in two
patches, to ease review).
The commit messages and tests provide many examples.

---

There could be many adjustment to these features, but I hope that if the
bulk of the code exists, adapting it will be easy.
One option, for example, is to do away with "--date-delta-format",
and accept the "-v" syntax in the "-d" string, so it will work
both from the command line and from a file:

    date -D "%F" -d "2019-10-31" -v "+2y -100h"
    printf "2019-10-31 +2y -100h" | date -D "%F" -f -

---

The attached patches are:

  tests: add 'date -r/--reference=FILE' test
  tests: add 'date -f/--file' (batch processing) test
  date: add -D/--date-format=FORMAT option
  date: add --date-delta-format=FORMAT option
  date: add -v/--adjust-date=STRING option
  date: expand -v=STR syntax to match FreeBSD

---

Comments and suggestions welcomed,
 - assaf

date-strp-2019-08-01.patch.gz
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