將歷史時間戳從UTC轉換爲本地

Question

我有一個文件，其中包含過去的時間戳，並且都是UTC。我需要將這些轉換爲東部時間。我已經接近了，但它在夏時制轉換中混亂了。

#!/usr/bin/perl 
use strict; 
use warnings; 
use Time::Piece; 

#DST not in effect 
my $utc = '2015-03-08 01:59:00.000'; 
my $local = utc_to_local($utc); 
print "DST not in effect: utc($utc) = local($local)\n"; 

#DST not in effect 
$utc = '2015-03-08 02:00:00.000'; 
$local = utc_to_local($utc); 
print "DST not in effect: utc($utc) = local($local)\n"; 


sub utc_to_local 
{ 
    my $utc_ts = $_[0]; #this has ms on right side, we want left 19 characters 
    $utc_ts = substr $utc_ts, 0, 19; 
    my $local_tp = localtime->strptime($utc_ts, '%Y-%m-%d %H:%M:%S'); 
    $local_tp = $local_tp + $local_tp->tzoffset(); 

    return $local_tp->strftime('%Y-%m-%d %H:%M:%S'); 
} 

正如你可以看到，如果我嘗試3/8 3/8凌晨2點UTC凌晨1:59。UTC，它認爲已經發生了變化，但凌晨2點UTC只有3/7在9 PM。遠離夏令時轉換，它可以正確地進行-5和-4偏移。

DST not in effect: utc(2015-03-08 01:59:00.000) = local(2015-03-07 20:59:00) 
DST not in effect: utc(2015-03-08 02:00:00.000) = local(2015-03-07 22:00:00) 

Answer 1

$utc_ts不是當地時間。

my $local_tp = localtime->strptime($utc_ts, '%Y-%m-%d %H:%M:%S'); 

應該

my $utc_tp = Time::Piece->strptime($utc_ts, '%Y-%m-%d %H:%M:%S'); 

---

然後是轉換的localtime的問題。

$local_tp = $local_tp + $local_tp->tzoffset(); 

應該

my $local_tp = localtime($utc_tp->epoch); 

---

一起：

#!/usr/bin/perl 
use strict; 
use warnings; 
use POSIX qw(); 
use Time::Piece; 

sub utc_to_local { 
    my ($utc_ts) = @_; 
    my $utc_tp = Time::Piece->strptime($utc_ts, '%Y-%m-%d %H:%M:%S'); 
    my $local_tp = localtime($utc_tp->epoch); 
    return $local_tp->strftime('%Y-%m-%d %H:%M:%S'); 
} 

sub local_to_utc { 
    my ($local_ts) = @_; 
    my $local_tp = Time::Piece->strptime($local_ts, '%Y-%m-%d %H:%M:%S'); 
    my $utc_tp = gmtime($local_tp->epoch); 
    return $utc_tp->strftime('%Y-%m-%d %H:%M:%S'); 
} 

{ 
    $ENV{TZ} = 'America/Toronto'; 
    POSIX::tzset(); 

    # DST not in effect 
    my $utc = '2015-03-08 06:59:00.000'; 
    my $local = utc_to_local(substr($utc, 0, -4)); 
    print "DST not in effect: utc($utc) = local($local)\n"; 

    # DST not in effect 
    $utc = '2015-03-08 07:00:00.000'; 
    $local = utc_to_local(substr($utc, 0, -4)); 
    print "DST not in effect: utc($utc) = local($local)\n"; 
} 

輸出：

DST not in effect: utc(2015-03-08 06:59:00.000) = local(2015-03-08 01:59:00) 
DST not in effect: utc(2015-03-08 07:00:00.000) = local(2015-03-08 03:00:00)