Re: difference in seconds between two formatted dates ...
On Sun, Dec 17, 2023 at 03:28:58PM +0000, Albretch Mueller wrote:
> On 12/17/23, Greg Wooledge <greg@wooledge.org> wrote:
> > On Sun, Dec 17, 2023 at 10:12:11AM +0000, Albretch Mueller wrote:
> >> ... after some long processing for which seconds would be exact
> >> enough, then I would like to get the seconds elapsed since dt00
> >
> > Are you working in bash, or sh?
>
> bash
>
> > Bash offers some alternatives, to avoid having to fork two date(1)
> > processes, light as those are. The first is:
> >
> > unicorn:~$ printf -v dt00 '%(%s)T' -1
> > unicorn:~$ echo "$dt00"
> > 1702821082
>
> but this is not what I meant and I am sure you can once again impress
> everyone here with your bash skills/wisdom. Is there such a thing as:
>
> dt00=$(date +%Y%m%d%H%M%S)
> printf -(whatever the formatting for seconds would be) "${dt00}%Y%m%d%H%M%S"
No, there is nothing in bash which scans date/time strings. You'd need
to use an external tool for this. GNU date is one such tool.
> I dealing with my "exposed mode" kinds of states ;-). I use a
> computer which initial state is kept as part of the file name as I
> explained, then as part of another ("exposed" or "private") reboot I
> want to check that file, so I would not be able to then simply do $((
> dt02 - dt00 ))
You've moved the goalposts. Now the state is not being kept WITHIN
a script, but in a FILE that's used by two separate scripts (one that
writes it, and one that has to interpret it).
This is a very different kind of problem.
You'll need to choose a tool or a language that can parse your chosen
storage format. This might be GNU date. This might be Perl, Python,
Tcl, or some other language that has appropriate facilities for parsing
date/time strings.
You'll also be strongly encouraged to choose a storage format that
facilitates such parsing. You might even want to work backwards --
figure out how you're going to parse the string, then choose the
format that works best with that specific parser.
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