[conspire] "Time zones exist to make programmers' lives miserable"

[Rick Moen]

Deirdre cited for me the Subject header as a saying by Jamis Buck, 
and it seemed amusing to quote, here.

Anyway, what follows is what _some_ of us do for fun on a Saturday
evening.

Extra credit question:  Why am I grepping out ".tab" and "posixrules" 
from the timezone names list?  Class?


----- Forwarded message from Wayne <Wayne at TradeTimer.com> -----

Date: Sat, 6 Feb 2021 17:33:03 -0800
From: Wayne <Wayne at TradeTimer.com>
To: Felton Linux Users Group LUG <felton-lug at googlegroups.com>
Subject: [Felton LUG] More online meeting fun...

In case you're interested, here is a partial list of time-practical online LUG meetings you might like to check out. I hope I got the time translations correct...

https://meet.jit.si/SurreyLUGBaB - 2nd and 4th Saturday, 11:00 to 17:00 UTC, 3AM-9AM PT
https://jitsimeet.jitsimeeting.co.uk/ManLUG - 3rd Saturday, 2-4PM UTC, 6AM PT
https://meet.jit.si/ALE-NW - every Sunday at 3PM ET, Noon PST
https://meet.jit.si/sf-lug.org - 1st Sunday, 11:00 AM PT
https://meet.jit.si/BerkeleyLUG - 2nd and 4th Sundays, 11AM PT
https://meet.jit.si/Pi.BerkeleyLUG - 3rd Sunday, 11AM PT
https://meet.jit.si/TheCall - every-other Monday, 8:30AM PT
https://meet.jit.si/livlug - 1st Wednesday 19:00 UTC, 11AM PST

More at the BALUG wiki...
https://www.wiki.balug.org/wiki/doku.php?id=balug:covid-19

----- End forwarded message -----
----- Forwarded message from Rick Moen <rick at linuxmafia.com> -----

Date: Sat, 6 Feb 2021 18:56:19 -0800
From: Rick Moen <rick at linuxmafia.com>
To: Felton Linux Users Group LUG <felton-lug at googlegroups.com>
Subject: Re: [Felton LUG] More online meeting fun...
Organization: If you lived here, you'd be $HOME already.

Quoting Wayne (Wayne at TradeTimer.com):

> In case you're interested, here is a partial list of time-practical
> online LUG meetings you might like to check out. I hope I got the time
> translations correct...

Time calculations involving multiple time zones are vexingly difficult.  
In fact, even _without_ multiple time zones, they're a pain.  E.g., 
this tiny shell script of mine is not entirely 100% correct because of 
an awkward definitional problem about when a day begins and ends for
purposes of day count:

$ cat $(which daysuntil)
#!/bin/sh
echo "Type the future date in ISO 8601 (YYYY-MM-DD) format."
read futuredate
echo $futuredate | tr -s '-' ' ' | awk '{dt=mktime($0 "00-00-00")-systime(); print int(dt/86400+1) " days";}'
$ 

I haven't been moved to improve it lately, but maybe will come back to
it.  Anyway, point is, doing a similar trick involving inputting a time
in zone X and programmatically converting it to zone Y seems like an
even more daunting task.  Anyone feeling cocky about that?  Maybe a
perlista?  ;->

What I _have_ done is the lazy 80% solution of saying "What is the time
_right now_ in zone Y?"  That's a lot simpler:

:r! grep worldclock .bashrc
    alias worldclock='zdump America/{Los_Angeles,Phoenix,Mexico_City,New_York,Toronto,Sao_Paulo} Europe/{London,Berlin,Oslo,Moscow} Asia/{Calcutta,Shanghai,Tokyo} Australia/{Perth,Melbourne} Pacific/Auckland'

I personally like that a lot.  It's elegant.

Sooner or later, I'll nail down the larger problem, maybe using this set
of Python tips:
https://stackoverflow.com/questions/10997577/python-timezone-conversion
With all these Zoom/Jitsi meet things happening all over the world, I
don't know about you, but I really need something like that -- and I
feel a little sheepish relying on some stranger's hidden-away script via
CGI, e.g, using things like
https://www.timeanddate.com/worldclock/converter.html .  That's not the
Unix way, Grasshopper.  ;->

----- End forwarded message -----
----- Forwarded message from Rick Moen <rick at linuxmafia.com> -----

Date: Sat, 6 Feb 2021 19:47:02 -0800
From: Rick Moen <rick at linuxmafia.com>
To: Felton Linux Users Group LUG <felton-lug at googlegroups.com>
Subject: Re: [Felton LUG] More online meeting fun...
Organization: If you lived here, you'd be $HOME already.

I wrote:

> Sooner or later, I'll nail down the larger problem...

Actually, I think this is a lot easier than I imagined.  Just manipulate
shell variable 'TZ' in scripting, and then ask date(1) to state what a
time in a certain specified time converts to, in the TZ-value zone:

$ TZ=MST date -d "19:43 EST"
Sat Feb  6 17:43:00 MST 2021
$ 

----- End forwarded message -----
----- Forwarded message from Rick Moen <rick at linuxmafia.com> -----

Date: Sat, 6 Feb 2021 21:06:13 -0800
From: Rick Moen <rick at linuxmafia.com>
To: Felton Linux Users Group LUG <felton-lug at googlegroups.com>
Subject: Re: [Felton LUG] More online meeting fun...
Organization: If you lived here, you'd be $HOME already.

I wrote:

> Actually, I think this is a lot easier than I imagined.  Just
> manipulate shell variable 'TZ' in scripting, and then ask date(1) to
> state what a time in a certain specified time converts to, in the
> TZ-value zone:
> 
> $ TZ=MST date -d "19:43 EST"
> Sat Feb  6 17:43:00 MST 2021
> $ 

Also, I made a little thing to let me type 'tzall' or 'tzall | less' or
'tzall | grep [something]' as the lazy way to find a timezone descriptor
for somewhere I care about.

Voila, a new shell function defined in my .bashrc:


    tzall () {
      find /usr/share/zoneinfo/* -type f -print | sed -r 's_/usr/share/zoneinfo/__' | grep -v -e .tab -e posixrules
    }


I first tried defining it as a shell _alias_ (out of habit), but the
gyrations you'd have to go through to escape the quotation characters
(for sed) seemed painful, so I did an end-run around that problem by
writing it as a shell function, instead.

There are a _whole_ lot of valid timezone names, many of them existing
for weird purposes.  There are actually 'only' 38 timezones in the
world[1] ; it's just that Linux systems let you refer to them by a lot
of distinct names.  How many names?

$ tzall | wc -l
1755
$ 

That many names.


[1] https://en.wikipedia.org/wiki/List_of_UTC_time_offsets

----- End forwarded message -----