godarda@gd:~$ R
...
> Sys.Date()
[1] "2020-06-18"

> Sys.time()
[1] "2020-06-18 17:41:48 IST"

> as.Date(Sys.Date())
[1] "2020-06-18"

> as.Date('2020/06/18')
[1] "2020-06-18"

> as.Date(Sys.Date(),format='%Y-%m-%d')
[1] "2020-06-18"

> as.Date('June 18, 2020',format='%B %d, %Y')
[1] "2020-06-18"

> as.Date('18JUN20',format='%d%b%y')
[1] "2020-06-18"

> weekdays(Sys.Date())
[1] "Thursday"
> date1 <- Sys.Date()
> date2 <- as.Date("2020-06-30")
> date1-date2
Time difference of -12 days
  
> date1
[1] "2020-06-18"

> date2
[1] "2020-06-30"

> date2-date1
Time difference of 12 days

> difftime(date2,date1,units="weeks")
Time difference of 1.714286 weeks

> date2 + 20
[1] "2020-07-20"

> difftime(date2+20,date1,units="weeks")
Time difference of 4.571429 weeks
> seq(Sys.Date(),by='days',length=12)
 [1] "2020-06-18" "2020-06-19" "2020-06-20" "2020-06-21" "2020-06-22"
 [6] "2020-06-23" "2020-06-24" "2020-06-25" "2020-06-26" "2020-06-27"
[11] "2020-06-28" "2020-06-29"

> seq(Sys.Date(),to=as.Date("2020-12-31"),by='4 weeks')
[1] "2020-06-18" "2020-07-16" "2020-08-13" "2020-09-10" "2020-10-08"
[6] "2020-11-05" "2020-12-03" "2020-12-31"