常用的輸出函數：cat()
常用的輸入函數：scan()，readline()，readLines()
(1) cat（）函數
Description
Outputs the objects, concatenating the representations. cat performs much less conversion than print.
Useage
cat(... , file = "", sep = " ", fill = FALSE, labels = NULL,append = FALSE)
參數介紹：
...：輸出對象
file:一個文件鏈接或者文件名，如果不寫此參數，表示輸出到控制台。
sep:分隔符
append:是否追加，當且僅當參數file是文件名而非鏈接時，此參數才有效。
例：
> cat(1:10)
1 2 3 4 5 6 7 8 9 10
把一個向量輸出到控制台。
> output <- file('output.txt') //建立鏈接
> class(output) //查看鏈接屬性，是connection
[1] "file" "connection"
> getwd() //獲取工作目錄
[1] "D:/Program Files/R/workspace"
> cat(1:100,sep='\t',file = output) //將向量存入文件鏈接指向的文件中，文件在工作目錄里。
> close(output) //關閉鏈接。
將一個向量輸出到文件中。
（2）scan()函數
Description
Read data into a vector or list from the console or file.
Usage
scan(file = "", what = double(), nmax = -1, n = -1, sep = "",quote = if(identical(sep, "\n")) "" else "'\"", dec = ".",skip = 0, nlines = 0, na.strings = "NA",
flush = FALSE, fill = FALSE, strip.white = FALSE,quiet = FALSE, blank.lines.skip = TRUE, multi.line = TRUE,comment.char = "", allowEscapes = FALSE,
fileEncoding = "", encoding = "unknown", text, skipNul = FALSE)
例：
> x <- scan()
1: 12
2: 12
3: 23
4:
Read 3 items
>
> x
[1] 12 12 23
利用鍵盤輸入三個數字，x里就會存儲三個數字。
也可以利用scan()函數讀取外部文件。例：
> y <- scan(file = 'output.txt')
Read 38 items
> y
[1] 1 2 3 4 5 6 7 8 9 101 2 3 4 5 6 7
[17] 8 9 101 2 3 4 5 6 7 8 9 10 11 12 13 14
[33] 15 16 17 18 19 20
讀取文件‘output.txt’里的數據。
(3)readline()函數
Description
readline reads a line from the terminal (in interactive use).
Usage
readline(prompt = "")
例：
> a <- readline()
hello world
> a
[1] "hello world"
與scan()不同，readline()函數只能輸入一行。
（4）readLines()函數
Description
Read some or all text lines from a connection.
Usage
readLines(con = stdin(), n = -1L, ok = TRUE, warn = TRUE,encoding = "unknown", skipNul = FALSE)
例：
conn <- file('output.txt')
a <- readLines(conn,n=1)
a
結果：
[1] "con\t"
b <- readLines(conn,n=5)
b
結果：
[1] "con\t"
[2] "a connection object or a character string."
[3] "n\t"
[4] "integer. The (maximal) number of lines to read. Negative values indicate that one should read up to the end of input on the connection."
[5] "ok\t"