strftime

        # Time.strftime

(from ruby core)
---
    time.strftime( string ) -> string

---

Formats *time* according to the directives in the given format string.

The directives begin with a percent (%) character. Any text not listed
as a directive will be passed through to the output string.

The directive consists of a percent (%) character, zero or more flags,
optional minimum field width, optional modifier and a conversion
specifier as follows:

    %<flags><width><modifier><conversion>

Flags:
    -  don't pad a numerical output
    _  use spaces for padding
    0  use zeros for padding
    ^  upcase the result string
    #  change case
    :  use colons for %z

The minimum field width specifies the minimum width.

The modifiers are "E" and "O". They are ignored.

Format directives:

    Date (Year, Month, Day):
      %Y - Year with century if provided, will pad result at least 4 digits.
              -0001, 0000, 1995, 2009, 14292, etc.
      %C - year / 100 (rounded down such as 20 in 2009)
      %y - year % 100 (00..99)

      %m - Month of the year, zero-padded (01..12)
              %_m  blank-padded ( 1..12)
              %-m  no-padded (1..12)
      %B - The full month name (``January'')
              %^B  uppercased (``JANUARY'')
      %b - The abbreviated month name (``Jan'')
              %^b  uppercased (``JAN'')
      %h - Equivalent to %b

      %d - Day of the month, zero-padded (01..31)
              %-d  no-padded (1..31)
      %e - Day of the month, blank-padded ( 1..31)

      %j - Day of the year (001..366)

    Time (Hour, Minute, Second, Subsecond):
      %H - Hour of the day, 24-hour clock, zero-padded (00..23)
      %k - Hour of the day, 24-hour clock, blank-padded ( 0..23)
      %I - Hour of the day, 12-hour clock, zero-padded (01..12)
      %l - Hour of the day, 12-hour clock, blank-padded ( 1..12)
      %P - Meridian indicator, lowercase (``am'' or ``pm'')
      %p - Meridian indicator, uppercase (``AM'' or ``PM'')

      %M - Minute of the hour (00..59)

      %S - Second of the minute (00..60)

      %L - Millisecond of the second (000..999)
           The digits under millisecond are truncated to not produce 1000.
      %N - Fractional seconds digits, default is 9 digits (nanosecond)
              %3N  millisecond (3 digits)
              %6N  microsecond (6 digits)
              %9N  nanosecond (9 digits)
              %12N picosecond (12 digits)
              %15N femtosecond (15 digits)
              %18N attosecond (18 digits)
              %21N zeptosecond (21 digits)
              %24N yoctosecond (24 digits)
           The digits under the specified length are truncated to avoid
           carry up.

    Time zone:
      %z - Time zone as hour and minute offset from UTC (e.g. +0900)
              %:z - hour and minute offset from UTC with a colon (e.g. +09:00)
              %::z - hour, minute and second offset from UTC (e.g. +09:00:00)
      %Z - Abbreviated time zone name or similar information.  (OS dependent)

    Weekday:
      %A - The full weekday name (``Sunday'')
              %^A  uppercased (``SUNDAY'')
      %a - The abbreviated name (``Sun'')
              %^a  uppercased (``SUN'')
      %u - Day of the week (Monday is 1, 1..7)
      %w - Day of the week (Sunday is 0, 0..6)

    ISO 8601 week-based year and week number:
    The first week of YYYY starts with a Monday and includes YYYY-01-04.
    The days in the year before the first week are in the last week of
    the previous year.
      %G - The week-based year
      %g - The last 2 digits of the week-based year (00..99)
      %V - Week number of the week-based year (01..53)

    Week number:
    The first week of YYYY that starts with a Sunday or Monday (according to %U
    or %W). The days in the year before the first week are in week 0.
      %U - Week number of the year. The week starts with Sunday. (00..53)
      %W - Week number of the year. The week starts with Monday. (00..53)

    Seconds since the Epoch:
      %s - Number of seconds since 1970-01-01 00:00:00 UTC.

    Literal string:
      %n - Newline character (\n)
      %t - Tab character (\t)
      %% - Literal ``%'' character

    Combination:
      %c - date and time (%a %b %e %T %Y)
      %D - Date (%m/%d/%y)
      %F - The ISO 8601 date format (%Y-%m-%d)
      %v - VMS date (%e-%^b-%4Y)
      %x - Same as %D
      %X - Same as %T
      %r - 12-hour time (%I:%M:%S %p)
      %R - 24-hour time (%H:%M)
      %T - 24-hour time (%H:%M:%S)

This method is similar to strftime() function defined in ISO C and
POSIX.

While all directives are locale independent since Ruby 1.9, %Z is
platform dependent. So, the result may differ even if the same format
string is used in other systems such as C.

%z is recommended over %Z. %Z doesn't identify the timezone. For
example, "CST" is used at America/Chicago (-06:00), America/Havana
(-05:00), Asia/Harbin (+08:00), Australia/Darwin (+09:30) and
Australia/Adelaide (+10:30). Also, %Z is highly dependent on the
operating system. For example, it may generate a non ASCII string on
Japanese Windows, i.e. the result can be different to "JST". So the
numeric time zone offset, %z, is recommended.

Examples:

    t = Time.new(2007,11,19,8,37,48,"-06:00") #=> 2007-11-19 08:37:48 -0600
    t.strftime("Printed on %m/%d/%Y")         #=> "Printed on 11/19/2007"
    t.strftime("at %I:%M %p")                 #=> "at 08:37 AM"

Various ISO 8601 formats:
    %Y%m%d           => 20071119                  Calendar date (basic)
    %F               => 2007-11-19                Calendar date (extended)
    %Y-%m            => 2007-11                   Calendar date, reduced accuracy, specific month
    %Y               => 2007                      Calendar date, reduced accuracy, specific year
    %C               => 20                        Calendar date, reduced accuracy, specific century
    %Y%j             => 2007323                   Ordinal date (basic)
    %Y-%j            => 2007-323                  Ordinal date (extended)
    %GW%V%u          => 2007W471                  Week date (basic)
    %G-W%V-%u        => 2007-W47-1                Week date (extended)
    %GW%V            => 2007W47                   Week date, reduced accuracy, specific week (basic)
    %G-W%V           => 2007-W47                  Week date, reduced accuracy, specific week (extended)
    %H%M%S           => 083748                    Local time (basic)
    %T               => 08:37:48                  Local time (extended)
    %H%M             => 0837                      Local time, reduced accuracy, specific minute (basic)
    %H:%M            => 08:37                     Local time, reduced accuracy, specific minute (extended)
    %H               => 08                        Local time, reduced accuracy, specific hour
    %H%M%S,%L        => 083748,000                Local time with decimal fraction, comma as decimal sign (basic)
    %T,%L            => 08:37:48,000              Local time with decimal fraction, comma as decimal sign (extended)
    %H%M%S.%L        => 083748.000                Local time with decimal fraction, full stop as decimal sign (basic)
    %T.%L            => 08:37:48.000              Local time with decimal fraction, full stop as decimal sign (extended)
    %H%M%S%z         => 083748-0600               Local time and the difference from UTC (basic)
    %T%:z            => 08:37:48-06:00            Local time and the difference from UTC (extended)
    %Y%m%dT%H%M%S%z  => 20071119T083748-0600      Date and time of day for calendar date (basic)
    %FT%T%:z         => 2007-11-19T08:37:48-06:00 Date and time of day for calendar date (extended)
    %Y%jT%H%M%S%z    => 2007323T083748-0600       Date and time of day for ordinal date (basic)
    %Y-%jT%T%:z      => 2007-323T08:37:48-06:00   Date and time of day for ordinal date (extended)
    %GW%V%uT%H%M%S%z => 2007W471T083748-0600      Date and time of day for week date (basic)
    %G-W%V-%uT%T%:z  => 2007-W47-1T08:37:48-06:00 Date and time of day for week date (extended)
    %Y%m%dT%H%M      => 20071119T0837             Calendar date and local time (basic)
    %FT%R            => 2007-11-19T08:37          Calendar date and local time (extended)
    %Y%jT%H%MZ       => 2007323T0837Z             Ordinal date and UTC of day (basic)
    %Y-%jT%RZ        => 2007-323T08:37Z           Ordinal date and UTC of day (extended)
    %GW%V%uT%H%M%z   => 2007W471T0837-0600        Week date and local time and difference from UTC (basic)
    %G-W%V-%uT%R%:z  => 2007-W47-1T08:37-06:00    Week date and local time and difference from UTC (extended)