问题
Time.new.month returns a single digit representation of any month prior to October (e.g. June is 6), but I want a 2-digit format (i.e. instead of 6 I want 06).
I wrote the following solution, and I am asking to see some other/better solutions.
s = 6.to_s; s[1]=s[0]; s[0] = '0'; s #=> '06'
回答1:
For your need I think the best is still
Time.strftime("%m")
as mentioned but for general use case the method I use is
str = format('%02d', 4)
puts str
depending on the context I also use this one which does the same thing:
str = '%02d %s %04d' % [4, "a string", 56]
puts str
Here is the documentation with all the supported formats: http://ruby-doc.org/core-2.3.1/Kernel.html#method-i-sprintf
回答2:
You can use this printf-like syntax:
irb> '%02d' % 6
=> "06"
or
str = '%02d' % 6
So:
s = '%02d' % Time.new.month
=> "06"
See the documentation for String#%.
回答3:
Mat's answer pointing out that you can use the % operator is great, but I would like to point out another way of doing it, using the rjust method of the String class:
str = 6.to_s.rjust(2,'0') # => "06"
回答4:
If you're trying to format an entire date or date and time (rather than just the month), you might want to use strftime:
m = Time.now.strftime('%m')
# => "06"
t = Time.now.strftime('%Y-%m-%dT%H:%M:%SZ%z')
# => "2011-06-18T10:56:22Z-0700"
That will give you easy access to all the usual date and time formats.
回答5:
You can use sprintf:
sprintf("%02d", s)
e.g. in irb:
>> sprintf("%02d", s)
=> "06"
来源：https://stackoverflow.com/questions/6397468/how-to-make-single-digit-number-a-two-digit-number-in-ruby