localtime gives unexpected result

Ghepardo has asked for the wisdom of the Perl Monks concerning the following question:

I am on a machine with "GB" (i.e. British) localisation, and I see the following:

$ perl -e '$t=0; print scalar localtime $t, "\n"; print scalar gmtime 
+$t'
Thu Jan  1 01:00:00 1970
Thu Jan  1 00:00:00 1970
[download]

So localtime and gmtime return different values for time "0".

Now I'd expect localtime and gmtime to return the same thing in Britain outside of a daylight savings time period (which 1 January is).

I wondered whether this was because I didn't have a TZ variable set in my environment, but setting this to 'Europe/London' made no difference.

We don't get this discrepancy if we use the current time:

$ perl -e '$t=time; print scalar localtime $t, "\n"; print scalar gmti
+me $t'
Tue Feb  7 20:24:24 2023
Tue Feb  7 20:24:24 2023
[download]

This feels like a stupid question, I think I must be missing something obvious...

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Re: localtime gives unexpected result by choroba (Cardinal) on Feb 07, 2023 at 20:55 UTC
Welcome to the wonderful human concept of measurable time. Daylight Saving Time Changes 1970 in London: > DST is observed all year during 1970 in London `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l]
Re^2: localtime gives unexpected result by Ghepardo (Novice) on Feb 07, 2023 at 22:53 UTC
Thanks @choroba, I would never have guessed that, especially since I was alive at the time (although fairly young). Use Perl, learn History (and a lot more besides).	[reply]
Re: localtime gives unexpected result by Anonymous Monk on Feb 08, 2023 at 04:02 UTC
It because of this in the timezone database: `# Zone NAME STDOFF RULES FORMAT [UNTIL] Zone Europe/London -0:01:15 - LMT 1847 Dec 1 0:00 GB-Eire %s 1968 Oct 27 1:00 - BST 1971 Oct 31 2:00u 0:00 GB-Eire %s 1996 0:00 EU GMT/BST` [download] So GB (Europe/London) was 01:00 offset from 1968 Oct 27 through to 1971 Oct 31 2AM. Apparently this was 'a three-year experiment was conducted with British Standard Time, keeping the clocks fixed throughout the year on GMT+1.'	[reply] [d/l]
Re^2: localtime gives unexpected result by Ghepardo (Novice) on Feb 08, 2023 at 09:31 UTC
Thanks @Anonymous Monk.	[reply]
Re: localtime gives unexpected result by Discipulus (Canon) on Feb 07, 2023 at 21:20 UTC
hello Ghepardo and welcome to the monastery and to the wonderful world of perl! beside `Welcome to the wonderful human concept of measurable time` also consider we are in XIII century and Perl rules the known world sorry I could not resist :) L* There are no rules, there are no thumbs.. Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.	[reply] [d/l] [select]
Re^2: localtime gives unexpected result by Ghepardo (Novice) on Feb 07, 2023 at 23:02 UTC
Thanks @Discipulus.	[reply]


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