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4.12: How do I find the day or week of the year?

    The localtime function returns the day of the year. Without an argument
    localtime uses the current time.

            $day_of_year = (localtime)[7];

    The "POSIX" module can also format a date as the day of the year or week
    of the year.

            use POSIX qw/strftime/;
            my $day_of_year  = strftime "%j", localtime;
            my $week_of_year = strftime "%W", localtime;

    To get the day of year for any date, use "POSIX"'s "mktime" to get a
    time in epoch seconds for the argument to localtime.

            use POSIX qw/mktime strftime/;
            my $week_of_year = strftime "%W",
                    localtime( mktime( 0, 0, 0, 18, 11, 87 ) );

    The "Date::Calc" module provides two functions to calculate these.

            use Date::Calc;
            my $day_of_year  = Day_of_Year(  1987, 12, 18 );
            my $week_of_year = Week_of_Year( 1987, 12, 18 );

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