Working with Go

Working with Date and Time

The time standard library provides the methods needed for working with dates and time in Go.

Now

Create a date using time.Now(), returns a Time type

now := time.Now()

Create a Unix timestamp, returns a int64 type

unix := time.Unix()

Format Date

Go uses a format-by-example method for formating dates. This is odd and you may never get used to it, I still haven't. There is a base date Monday, January 2nd, 2006 at 15:04:05 and all formats specified are based off examples using that date.

If you want a date in YYYY-MM-DD format, you would use 2006-01-02 as the format string.

It is debatable what is easier to remember? The sample date or the %b %c formats other languages use. A way to try to remember is Month=1, Day=2, Hour=3, Minute=4, Sec=5, Year=6

fmt.Println(now.Format("Mon, Jan 2, 2006 at 3:04pm"))

Use a method to get any part of the date, see Time documentation for list of available time methods.

fmt.Println("Year: ", now.Year())
fmt.Println("Month: ", now.Month())

Built-in Formats

The time library contains a set of built-in constants to assist with standard date formatting.

const (
  ANSIC      : "Mon Jan _2 15:04:05 2006"
  UnixDate   : "Mon Jan _2 15:04:05 MST 2006"
  RubyDate   : "Mon Jan 02 15:04:05 -0700 2006"
  RFC822     : "02 Jan 06 15:04 MST"
  RFC822Z    : "02 Jan 06 15:04 -0700" // RFC822 with numeric zone
  RFC850     : "Monday, 02-Jan-06 15:04:05 MST"
  RFC1123    : "Mon, 02 Jan 2006 15:04:05 MST"
  RFC1123Z   : "Mon, 02 Jan 2006 15:04:05 -0700" // RFC1123 with numeric zone
  RFC3339    : "2006-01-02T15:04:05Z07:00"
  RFC3339Nano: "2006-01-02T15:04:05.999999999Z07:00"
  Kitchen    : "3:04PM"
  // Handy time stamps.
  Stamp     : "Jan _2 15:04:05"
  StampMilli: "Jan _2 15:04:05.000"
  StampMicro: "Jan _2 15:04:05.000000"
  StampNano : "Jan _2 15:04:05.000000000"
)

An example using the constant formats

fmt.Println(now.Format(time.RFC850))
fmt.Println(now.Format(time.RFC1123))

Setting a Specific Date

A time zone is required when specifying a date, you can build a time zone using the LoadLocation, or you could also use the time.UTC constant for UTC.

est, _ := time.LoadLocation("EST")
july4 := time.Date(1776, 7, 4, 12, 15, 0, 0, est)

Parse Dates

You can parse user inputted dates using known formats by specifying the format by example

input_format := "1/2/2006 3:04pm"
user_str := "4/16/2014 11:38am"
user_date, err := time.Parse(input_format, user_str)
if err != nil {
    fmt.Println(">>> Error parsing date string")
}
fmt.Println("User date:  ", user_date.Format("Jan 2, 2006 @ 3:04pm"))

Date/Time Comparisons

You can use Before(), After(), or Equal() to compare dates.

if july4.Before(now) {
    fmt.Println("July 4 is before Now ")
}

Date Arithmetic

The Time library also includes a Duration type which represents the different between two dates. The Duration type does not include days due to timezones and daylight savings.

Calculate a Duration:

diff := now.Sub(july4)

Use a Duration:

fmt.Printf("July 4 was about %d hours ago \n", diff.Hours())

You can add dates using Durations

twodaysDiff := time.Hour * 24 * 2
twodays := now.Add(twodaysDiff)
fmt.Println("Two Days: ", twodays.Format(time.ANSIC))