Handling stdin in Go

Internal

• Go Code Examples
• Go Strings
• fmt Package

Handling stdin with bufio.NewReader().ReadString()

"Command line" loop:

r := bufio.NewReader(os.Stdin)
for {
  fmt.Print("> ")
  lineb, _, err := r.ReadLine()
  if err != nil {
    return
  }
  line := string(lineb)
  if line == "exit" {
    return
  }
}

Note that the string contains the trailing \n. You can remove it with strings.Trim().

Handling stdin with fmt Functions

Reading lines of input from stdin, as individual strings, with fmt.Scan* functions is somewhat inconvenient. The library seems to want to tokenize the string and store fragments into different variables. That could be a good pattern if you get used with it, but to read lines "in bulk", use bufio.NewReader().ReadString().

fmt.Scan()

https://golang.org/pkg/fmt/#Scan

Read text from stdin. It stores successive space-separated values into successive arguments. Newlines count as space. It returns the number of items successfully scanned. If that is less than the number of arguments, err will report why.

var s string
cnt, err := fmt.Scan(&s)
fmt.Printf("input line: %s, cnt: %d, error: %s\n", s, cnt, err)

fmt.Scanln()

https://golang.org/pkg/fmt/#Scanln

Scanln is similar to Scan, but stops scanning at a newline or EOF. It still uses space as separator, and stores space-separated fragments into successive arguments.

var line string
fmt.Scanln(&line)

fmt.Scanf()

https://golang.org/pkg/fmt/#Scanf

var f float
cnt, err := fmt.Scanf("%f", &f)