| readline {base} | R Documentation | 
readline reads a line from the terminal
readline(prompt = "")
prompt | 
the string printed when prompting the user for input.
Should usually end with a space " ". | 
The prompt string will be truncated to a maximum allowed length, normally 256 chars (but can be changed in the source code).
A character vector of length one.
fun <- function() {
  ANSWER <- readline("Are you a satisfied R user? ")
  if (substr(ANSWER, 1, 1) == "n")
    cat("This is impossible.  YOU LIED!\n")
  else
    cat("I knew it.\n")
}
fun()