Ruby strftime: 没有前导0的月份？

Some versions of strftime do allow prefixing with minus to format out leading zeros, for eg:

strftime "%-d/%-m/%y"

However this will depend on strftime on your system. So for consistency I would do something like this instead:

dt = Time.local(2010, 'Sep', 1)
printf "%d/%d/%d", dt.day, dt.month, dt.year

Here's the formatting list I go off of. This is from the docs for 2.1.3. According to this you would want %-m:

Date (Year, Month, Day):
%Y - Year with century (can be negative, 4 digits at least)
-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.


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)

Updated to latest 2.1.3 docs on 10/24/14

I had a similar problem and fixed it by converting strftime("%m") into an integer.

For example:

strftime("%m")+0 give the current month as integer 'without leading zero'

Simple, though not elegant.

Docs show a number of different options for configuring number format. Adding to the %-d format, you can also use these flags in place of "-":

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.