格式化时间

例如有个时间t = Time.now，格式化有：
t.to_s(:long)
t.to_s(:short)
t.to_s(:db)
还可以调用strftime方法加以参数：
参看其参数,运行：ri Time.strftime
Format meaning:
       %a - The abbreviated weekday name (``Sun'')
       %A - The  full  weekday  name (``Sunday'')
       %b - The abbreviated month name (``Jan'')
       %B - The  full  month  name (``January'')
       %c - The preferred local date and time representation
       %d - Day of the month (01..31)
       %H - Hour of the day, 24-hour clock (00..23)
       %I - Hour of the day, 12-hour clock (01..12)
       %j - Day of the year (001..366)
       %m - Month of the year (01..12)
       %M - Minute of the hour (00..59)
       %p - Meridian indicator (``AM''  or  ``PM'')
       %S - Second of the minute (00..60)
       %U - Week  number  of the current year,
               starting with the first Sunday as the first
               day of the first week (00..53)
       %W - Week  number  of the current year,
               starting with the first Monday as the first
               day of the first week (00..53)
       %w - Day of the week (Sunday is 0, 0..6)
       %x - Preferred representation for the date alone, no time
       %X - Preferred representation for the time alone, no date
       %y - Year without a century (00..99)
       %Y - Year with century
       %Z - Time zone name
       %% - Literal ``%'' character
    
        t = Time.now
        t.strftime("Printed on %m/%d/%Y")   #=> "Printed on 04/09/2003"
        t.strftime("at %I:%M%p")            #=> "at 08:56AM"

这样可以自定义时间格式。

这个可以显示所调用的时间点距离现在的时间差：
def relative_time
    diff_seconds = (Time.now - self).to_i
    case diff_seconds
      when 0 .. 59
        "#{diff_seconds}秒钟前"
      when 60..(3600-1)
        "#{diff_seconds/60}分钟前"
      when 3600..(3600*24-1)
        "#{diff_seconds/3600}小时前"
      when (3600*24)..(3600*24*30)
        "#{diff_seconds/(3600*24)}天前"
      else
        self.strftime("%Y-%m-%d")
    end
  end

这是网上的一段代码：

module PrettyDate
def to_pretty
a = (Time.now-self).to_i

case a
  when 0 then return 'just now'
  when 1 then return 'a second ago'
  when 2..59 then return a.to_s+' seconds ago' 
  when 60..119 then return 'a minute ago' #120 = 2 minutes
  when 120..3540 then return (a/60).to_i.to_s+' minutes ago'
  when 3541..7100 then return 'an hour ago' # 3600 = 1 hour
  when 7101..82800 then return ((a+99)/3600).to_i.to_s+' hours ago' 
  when 82801..172000 then return 'a day ago' # 86400 = 1 day
  when 172001..518400 then return ((a+800)/(60*60*24)).to_i.to_s+' days ago'
  when 518400..1036800 then return 'a week ago'
end
return ((a+180000)/(60*60*24*7)).to_i.to_s+' weeks ago'
end
end

Time.send :include, PrettyDate