Date Trickiness

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

Greetings Fellow Monestary Inhabitants, I come, humbly beseeching the assistance of the Monks, Saints, Prelates, etc on a Date, particularly POSIX::strftime, problem I've found.

The Setup

I ahve a perl script that runds on a Win2K box via scheduler and parses some network logs. The way it knows what to do is get today's date with

my $time = POSIX::strftime "%Y%m%d",localtime;

and them the following happens to parse yesterday's files:

my $newtime = ($time -1);
my $log = $newtime.".log";
[download]

As many of you already can see, things broke this morning because 20041001 -1 is 20041000 and not 20040930. So, I'm looking for a fix. I've dug a bit through CPAN and looked at Activestates's info. Many possible modules don't want to compile properly on Win32.

Another complication, I use pp to package my scripts into Win32 executables.

Thanks for any and all assistance,

monger

Monger +++++++++++++++++++++++++ Munging Perl on the side

Comment on Date Trickiness Select or Download Code

Replies are listed 'Best First'.
Re: Date Trickiness by VSarkiss (Monsignor) on Oct 01, 2004 at 18:11 UTC
Here's another way: `my $time = POSIX::strftime "%Y%m%d",localtime; sleep 86400; # wait until tomorrow :-) my $log = $time . ".log";` [download] I can't take credit for this, it comes from dominus's wonderful Infrequently asked questions list. Update Well, at least I thought it was. I can't seem to find it on there anymore....	[reply] [d/l]
Re^2: by Zed_Lopez (Chaplain) on Oct 01, 2004 at 19:00 UTC
It's still there.	[reply]
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Re: Date Trickiness by blokhead (Monsignor) on Oct 01, 2004 at 18:13 UTC
I like using Time::Local whenever I can because it's fast and a core module. By combining localtime and timelocal_nocheck, you can do simple date manipulation: `#/usr/bin/perl -l use POSIX 'strftime'; use Time::Local 'timelocal_nocheck'; my ($d, $m, $y) = (localtime)[3,4,5]; my $yesterday = timelocal_nocheck 0, 0, 0, $d - 1, $m, $y; my $fivehundred = timelocal_nocheck 0, 0, 0, $d + 500, $m, $y; print "Today: ", strftime "%Y%m%d", localtime; print "Yesterday: ", strftime "%Y%m%d", localtime $yesterday; print "In 500 days: ", strftime "%Y%m%d", localtime $fivehundred; __END__ Today: 20041001 Yesterday: 20040930 In 500 days: 20060213` [download] I like timelocal_nocheck for simple date addition/subtraction because it will DWYM when you ask for something like "the 0th day of October" (as we do in this example) or "the 20,000th second of January." See the POD for more info & examples. Update: added ridiculous +500 days example blokhead	[reply] [d/l]
Re^2: Date Trickiness by monger (Friar) on Oct 01, 2004 at 19:07 UTC
Thanks for the info blockhead. That'll go in for future use for sure. Used bmann's quickie, but your's is an excellent compliment. monger Monger +++++++++++++++++++++++++ Munging Perl on the side	[reply]
Re: Date Trickiness by bmann (Priest) on Oct 01, 2004 at 18:06 UTC
Use localtime to get the date 24 hours ago `my $newtime= POSIX::strftime "%Y%m%d", localtime(time - 60 * 60 * 24);`	[reply] [d/l]
Re^2: Date Trickiness by pijll (Beadle) on Oct 02, 2004 at 08:24 UTC
Note that this can go wrong at DST changes, when a day is shorter or longer than 24 hours. If you want it to work on those days to, either use gmtime instead of localtime, run the script during daytime (or at least, not between 23:00 and 1:00), or use a module (such as DateTime).	[reply]
Re^2: Date Trickiness by monger (Friar) on Oct 01, 2004 at 19:06 UTC
Thanks bmann. That did the trick. monger Monger +++++++++++++++++++++++++ Munging Perl on the side	[reply]
Re: Date Trickiness by Zed_Lopez (Chaplain) on Oct 01, 2004 at 18:04 UTC
Date::Pcalc is a pure Perl implementation of Date::Calc and date arithmetic is what it does bestest.	[reply]
Re: Date Trickiness by johnnywang (Priest) on Oct 01, 2004 at 19:39 UTC
I always use Date::Manip, it actually understands words like "today" and "yesterday": `use Date::Manip; my $today = UnixDate( ParseDate("today"), "%Y%m%d"); my $yesterday = UnixDate( ParseDate("yesterday"), "%Y%m%d");` [download]	[reply] [d/l]