(part of the standard Perl distribution), but mathematical operations
are consequently slower.
+If precision is important, such as when dealing with money, it's good
+to work with integers and then divide at the last possible moment.
+For example, work in pennies (1995) instead of dollars and cents
+(19.95) and divide by 100 at the end.
+
To get rid of the superfluous digits, just use a format (eg,
C<printf("%.2f", 19.95)>) to get the required precision.
See L<perlop/"Floating-point Arithmetic">.
$day_of_year = (localtime(time()))[7];
-or more legibly (in 5.004 or higher):
+or more legibly (in 5.7.1 or higher):
- use Time::localtime;
- $day_of_year = localtime(time())->yday;
+ use Time::Piece;
+ $day_of_year = localtime->day_of_year();
-You can find the week of the year by dividing this by 7:
+You can find the week of the year by using Time::Piece's strftime():
- $week_of_year = int($day_of_year / 7);
+ $week_of_year = localtime->strftime("%U");
+ $iso_week = localtime->strftime("%V");
-Of course, this believes that weeks start at zero. The Date::Calc
-module from CPAN has a lot of date calculation functions, including
-day of the year, week of the year, and so on. Note that not
-all businesses consider ``week 1'' to be the same; for example,
-American businesses often consider the first week with a Monday
-in it to be Work Week #1, despite ISO 8601, which considers
-WW1 to be the first week with a Thursday in it.
+The difference between %U and %V is that %U assumes that the first day
+of week 1 is the first Sunday of the year, whereas ISO 8601:1988 uses
+the first week that has at least 4 days in the current year, and with
+Monday as the first day of the week. You can also use %W, which will
+return the week of the year with Monday as the first day of week 1. See
+your strftime(3) man page for more details.
=head2 How do I find the current century or millennium?
Date::Calc modules from CPAN before you go hacking up your own parsing
routine to handle arbitrary date formats.
+Also note that the core module Time::Piece overloads the addition and
+subtraction operators to provide date calculation options. See
+L<Time::Piece/Date Calculations>.
+
=head2 How can I take a string and turn it into epoch seconds?
If it's a regular enough string that it always has the same format,
=head2 How can I find the Julian Day?
-Use the Time::JulianDay module (part of the Time-modules bundle
-available from CPAN.)
+Use Time::Piece as follows:
+
+ use Time::Piece;
+ my $julian_day = localtime->julian_day;
+ my $mjd = localtime->mjd; # modified julian day
-Before you immerse yourself too deeply in this, be sure to verify that it
-is the I<Julian> Day you really want. Are you really just interested in
-a way of getting serial days so that they can do date arithmetic? If you
+Before you immerse yourself too deeply in this, be sure to verify that
+it is the I<Julian> Day you really want. Are you interested in a way
+of getting serial days so that you just can tell how many days they
+are apart or so that you can do also other date arithmetic? If you
are interested in performing date arithmetic, this can be done using
-either Date::Manip or Date::Calc, without converting to Julian Day first.
-
-There is too much confusion on this issue to cover in this FAQ, but the
-term is applied (correctly) to a calendar now supplanted by the Gregorian
-Calendar, with the Julian Calendar failing to adjust properly for leap
-years on centennial years (among other annoyances). The term is also used
-(incorrectly) to mean: [1] days in the Gregorian Calendar; and [2] days
-since a particular starting time or `epoch', usually 1970 in the Unix
-world and 1980 in the MS-DOS/Windows world. If you find that it is not
-the first meaning that you really want, then check out the Date::Manip
-and Date::Calc modules. (Thanks to David Cassell for most of this text.)
+Time::Piece (standard module since Perl 5.8), or by modules
+Date::Manip or Date::Calc.
+
+There is too many details and much confusion on this issue to cover in
+this FAQ, but the term is applied (correctly) to a calendar now
+supplanted by the Gregorian Calendar, with the Julian Calendar failing
+to adjust properly for leap years on centennial years (among other
+annoyances). The term is also used (incorrectly) to mean: [1] days in
+the Gregorian Calendar; and [2] days since a particular starting time
+or `epoch', usually 1970 in the Unix world and 1980 in the
+MS-DOS/Windows world. If you find that it is not the first meaning
+that you really want, then check out the Date::Manip and Date::Calc
+modules. (Thanks to David Cassell for most of this text.)
=head2 How do I find yesterday's date?
Then you can pass this to C<localtime()> and get the individual year,
month, day, hour, minute, seconds values.
+Alternatively, you can use Time::Piece to subtract a day from the value
+returned from C<localtime()>:
+
+ use Time::Piece;
+ use Time::Seconds; # imports seconds constants, like ONE_DAY
+ my $today = localtime();
+ my $yesterday = $today - ONE_DAY;
+
Note very carefully that the code above assumes that your days are
twenty-four hours each. For most people, there are two days a year
when they aren't: the switch to and from summer time throws this off.
If you are serious about writing a parser, there are a number of
modules or oddities that will make your life a lot easier. There are
the CPAN modules Parse::RecDescent, Parse::Yapp, and Text::Balanced;
-and the byacc program.
+and the byacc program. Starting from perl 5.8 the Text::Balanced
+is part of the standard distribution.
One simple destructive, inside-out approach that you might try is to
pull out the smallest nesting parts one at a time:
If @in is sorted, and you want @out to be sorted:
(this assumes all true values in the array)
- $prev = 'nonesuch';
+ $prev = "not equal to $in[0]";
@out = grep($_ ne $prev && ($prev = $_, 1), @in);
This is nice in that it doesn't use much extra memory, simulating
For some specific applications, you can use one of the DBM modules.
See L<AnyDBM_File>. More generically, you should consult the FreezeThaw,
-Storable, or Class::Eroot modules from CPAN. Here's one example using
+Storable, or Class::Eroot modules from CPAN. Starting from Perl 5.8
+Storable is part of the standard distribution. Here's one example using
Storable's C<store> and C<retrieve> functions:
use Storable;
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