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

Hello Monks!

One of my daily running applications (6am) needs the yesterdays date, or better the date of $param-1day.

Yesterday, sunday, was here in germany the change from 2am to 3am. Running on sunday with date=20100328 it was correct yday=20100327. But I got today with date=20100329 yday=20100327 again.

Code for this:

#!/bin/perl
use strict;
use Time::Local;

die "Wrong parameter count." unless scalar(@ARGV) == 1;
die "Wrong parameter format." unless $ARGV[0] =~ /(\d{4})(\d{2})(\d{2}
+)/;

my @d = localtime(timelocal(0, 0, 0, $3, $2-1, $1) - 86400);
printf("%04d%02d%02d", ($d[5]+1900), $d[4]+1, $d[3]);

[download]

My question is now how I can fix this issue?

I searched for another module wich help me on this, but Date::Manip have the same problems (reported in "Known Bugs") and Date::Calc have to much dependencies that I have to install, just for task.

Greetings, Schaelle

Replies are listed 'Best First'.
Re: Yesterdays date while daylight saving time change
by moritz (Cardinal) on Mar 29, 2010 at 08:44 UTC
    Date::Simple to the rescue: 
    $ perl -MDate::Simple=today -wle 'print today() - 1'
2010-03-28

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    (Update:) Of course this can be generalized to get the previous date from any other date: 

    $ perl -MDate::Simple=date -wle 'print date("2010-04-01") - 1'
2010-03-31

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    Or in fact going any number of days forwards or backwards.

    Perl 6 - links to (nearly) everything that is Perl 6.
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[d/l]
[select]

      This would be another solution than, because it's also just one module (like in my solution) with no dependencies.

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Re: Yesterdays date while daylight saving time change
by JavaFan (Canon) on Mar 29, 2010 at 08:43 UTC
    Since you only want the date, don't take the date of 86400 (24 hours) seconds before midnight. Take 43200 (12 hours) before midnight - that should work unless you live in a piece of the world that shifts 12 hours during DST change over. Or use 86400 seconds before midday.
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      Used this solution and just subtract only 12 hours instead of 24 hours. works with only 1 hour subtraction too. Thanks all!
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        Used this solution and just subtract only 12 hours instead of 24 hours. works with only 1 hour subtraction too.
        If you use a 1 hour subtraction, you'll be back here in half a year when it fails because of a DST change in the other direction.
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Re: Yesterdays date while daylight saving time change
by Corion (Patriarch) on Mar 29, 2010 at 08:43 UTC

    I prefer to do my date math by repeatedly adding/subtracting 22 hours until the day part of the date changes. Another approach is to Just Not Schedule Anything In The 02:00 To 03:00 Time Slot :).

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[d/l]
      Another approach is to Just Not Schedule Anything In The 02:00 To 03:00 Time Slot
      Actually, that wasn't the OPs problem. (And it's not everywhere in Europe that clocks move at 02:00 - Europe moves at 01:00 UTC, which is 02:00 local time in large parts of Europe, but 01:00 local time in the UK, Ireland, and Portugal, and 03:00 local time further East). In fact, if he had done the calculations based from a 02:00 timestamp, he wouldn't not have run into problems. Assuming a DST shift of one hour, the OP could do his calculation of taking the date of the time 24 hours earlier if the time component is between 01:00:00 and 22:59:59.
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