Go read input
last modified April 11, 2024
In this article we show how to read input from a user. Standard input, often abbreviated stdin, is a stream from which a program reads its input data.
To read input from users in Go, we use the fmt, bufio,
and os packages.
$ go version go version go1.22.2 linux/amd64
We use Go version 1.22.2.
Go read input with Scanf
The Scanf function scans text read from standard input,
storing successive space-separated values into successive arguments as
determined by the format. It returns the number of items successfully scanned.
package main
import "fmt"
func main() {
var name string
fmt.Print("Enter your name: ")
fmt.Scanf("%s", &name)
fmt.Println("Hello", name)
}
The example prompts the user to enter his name.
var name string
We define a string variable.
fmt.Scanf("%s", &name)
The entered value is stored into the name variable.
$ go run read_input.go Enter your name: Peter Hello Peter
We run the program and enter a name.
In the next example, we read two values.
package main
import "fmt"
func main() {
var name string
var age int
fmt.Print("Enter your name & age: ")
fmt.Scanf("%s %d", &name, &age)
fmt.Printf("%s is %d years old\n", name, age)
}
The program reads a name and age from the user.
fmt.Scanf("%s %d", &name, &age)
The Scanf function reads a string and an integer to the two provided
variables.
$ go run read_input2.go Enter your name & age: Peter 34 Peter is 34 years old
Go read input with NewReader
The bufio package implements buffered I/O. Buffered I/O has much
better performance than non-buffered. The package wraps an io.Reader
or io.Writer object, creating another object (Reader or Writer)
that also implements the interface but provides buffering and some help for
textual I/O.
package main
import (
"os"
"bufio"
"fmt"
)
func main() {
reader := bufio.NewReader(os.Stdin)
fmt.Print("Enter your name: ")
name, _ := reader.ReadString('\n')
fmt.Printf("Hello %s\n", name)
}
The program reads a name from the input using bufio.NewReader.
reader := bufio.NewReader(os.Stdin)
We pass the standard input to the bufio.NewReader.
name, _ := reader.ReadString('\n')
The ReadString reads until the first occurrence of the specified
delimiter (new-line in our case) in the input, returning a string containing the
data up to and including the delimiter.
Go read input with NewScanner
The Scanner provides a convenient interface for reading data
such as a file of newline-delimited lines of text.
package main
import (
"bufio"
"fmt"
"os"
)
func main() {
names := make([]string, 0)
scanner := bufio.NewScanner(os.Stdin)
for {
fmt.Print("Enter name: ")
scanner.Scan()
text := scanner.Text()
if len(text) != 0 {
fmt.Println(text)
names = append(names, text)
} else {
break
}
}
fmt.Println(names)
}
The example allows to read multiple names from the user. Press enter without value to finish the program.
names := make([]string, 0)
We create an empty slice.
scanner := bufio.NewScanner(os.Stdin)
A new scanner is created from the standard input.
for {
fmt.Print("Enter name: ")
...
In a for loop, we repeatedly ask the user for a name.
scanner.Scan()
We read a line from standard input. The Scan advances the Scanner
to the next token, which will then be available through the Bytes
or Text function.
text := scanner.Text()
The Text returns the most recent token generated by a call to
Scan as a newly allocated string holding its bytes.
if len(text) != 0 {
fmt.Println(text)
names = append(names, text)
} else {
break
}
If the text is not empty, we print it and append it to the slice.
fmt.Println(names)
Finally, we print all the scanned names.
$ go run read_input3.go Enter name: Lucia Lucia Enter name: Peter Peter Enter name: Roman Roman Enter name: Jane Jane Enter name: [Lucia Peter Roman Jane]
Source
In this article we have covered ways to read input from a user in Golang.
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