substr() function extract or replace substrings in a character vector.

substr(x, start, stop)
substring(text, first, last = 1000000L)
substr(x, start, stop) <- value
substring(text, first, last = 1000000L) <- value

x,text: character vector
start, first: integer, the first element to be replaced
stop, last: integer, the last element to be replaced
value: character vector, recycled if necessary

> substr("tutorial",2,3)

[1] "ut"

> x <- c("green","red","blue")
> substr(x,2,3)

[1] "re" "ed" "lu"

> substring(x,2,3)

[1] "re" "ed" "lu"