在提示输入文本“ Enter input”之前，如何检查os.stdin

Question

I have to promt for some input from os.stdin.How can I check this is available for reading before printing statements like "Enter your text" and then read from input.If stdin is not available it is printing bad file descriptor after "Enter your text". how to avoid this?

package main
import (
    "bufio"
    "os"
    "io"
    "fmt"
)
func main(){
consSource := NewConsoleAccessTokenSource("www.google.co.in", os.Stdin)
fmt.Print("Token: ")
    consSource.scanner.Scan()
    err := consSource.scanner.Err()
    if err != nil {
        fmt.Print(err)
    }
    fmt.Print(consSource.scanner.Text())
}
func NewConsoleAccessTokenSource(websiteUrl string, reader io.Reader) *ConsoleAccessTokenSource {
    s := &ConsoleAccessTokenSource{}
    s.WebsiteUrl = websiteUrl
    s.scanner = bufio.NewScanner(reader)
    return s
}
type ConsoleAccessTokenSource struct {
    WebsiteUrl string

    scanner *bufio.Scanner
}

This is what I am trying to do .when I run this program using "nohup executable" it is giving bad file descriptor.

Answer 1

os.Stdin is an exported variable of the os package, it is of type *os.File.

You may call File.Stat() on it to see if it's available and also to get additional info about it (e.g. if it is being piped or its source is a terminal):

if _, err := os.Stdin.Stat(); err != nil {
    fmt.Println("Stdin not available:", err)
} else {
    fmt.Println("Stdin available.")
}

Let's see an example when it's not available. It won't be if we close it first e.g. with the File.Close() method:

fmt.Println("Closing:", os.Stdin.Close())

if _, err := os.Stdin.Stat(); err != nil {
    fmt.Println("Stdin not available:", err)
} else {
    fmt.Println("Stdin available.")
}

Output (try it on the Go Playground):

Stdin available.
Closing: <nil>
Stdin not available: stat /dev/stdin: Bad file number

Also check related question: Check if there is something to read on STDIN in Golang