targets: "2019,3,1", "2019,03,01", "2019.03.01", "2019-03-01", " '21/3/1"
-------------------------------------------------------------------------

```
year<-c("2019,3,1", "2019,03,01", "2019.03.01", "2019-03-01", " '21/3/1", "2019,3-1", "2019-03=01", "2019,03.01", "2019/03-01", "2019-350-01")

grep("",year,value=T)

```

I tried

```
grep("[20 ']19([,./-]0?[3])[,./-](0?[1])$",year,value=T)

```

but I still have "2019,3-1" "2019,03.01" "2019/03-01"