bash

% go run ulid/ulid.go
Unixtime with nanosec
01F3W0VG46FH5P40MEEY68ME80
01F3W0VG467PHG5QEV57V2K7PF
01F3W0VG46GSWCC2GEC8G0N3WW
01F3W0VG46PX26DX5B59Q2GPX3
Unixtime with sec
01F3W0VG0GAH38AX7EJ2NJ557A
01F3W0VG0GAH38AX7EJ2NJ557A
01F3W0VG0GAH38AX7EJ2NJ557A
01F3W0VG0GAH38AX7EJ2NJ557A
...but dont create entropy(io.Reader) everytime.
01F3W0VG0GAH38AX7EJ2NJ557A
01F3W0VG0GAH38AX7EJ5Y176FG
01F3W0VG0GAH38AX7EJ7AKEDC3
01F3W0VG0GAH38AX7EJ7W4GKJS

ulid.go

package main

import (
	"fmt"
	"math/rand"
	"time"

	"github.com/oklog/ulid"
)

func main() {
	{
		gen1 := func() string {
			now := time.Now()
			t := now.UnixNano()
			entropy := ulid.Monotonic(rand.New(rand.NewSource(t)), 0)
			id := ulid.MustNew(ulid.Timestamp(now), entropy).String()
			return id
		}

		gen2 := func() string {
			t := time.Unix(time.Now().Unix(), 0)
			entropy := ulid.Monotonic(rand.New(rand.NewSource(t.UnixNano())), 0)
			id := ulid.MustNew(ulid.Timestamp(t), entropy).String()
			return id
		}

		var gen3 func() string
		{
			t := time.Unix(time.Now().Unix(), 0)
			entropy := ulid.Monotonic(rand.New(rand.NewSource(t.UnixNano())), 0)

			gen3 = func() string {
				id := ulid.MustNew(ulid.Timestamp(t), entropy).String()
				return id
			}

		}
		fmt.Println("Unixtime with nanosec")
		fmt.Println(gen1())
		fmt.Println(gen1())
		fmt.Println(gen1())
		fmt.Println(gen1())

		fmt.Println("Unixtime with sec")
		fmt.Println(gen2())
		fmt.Println(gen2())
		fmt.Println(gen2())
		fmt.Println(gen2())

		fmt.Println("...but dont create entropy(io.Reader) everytime.")
		fmt.Println(gen3())
		fmt.Println(gen3())
		fmt.Println(gen3())
		fmt.Println(gen3())

	}
}