检测STDIN上是否有东西

Question

Program should be able to get input from stdin on terminal, as follows:

echo foobar | program

However, in the source below for Program, the stdin read blocks if the pipe is omitted:

package main

import (
    "fmt"
    "os"
)

func main() {
    b := make([]byte, 1024)
    r := os.Stdin
    n, e := r.Read(b)
    if e != nil {
        fmt.Printf("Err: %s
", e)
    }
    fmt.Printf("Res: %s (%d)
", b, n)

}

So how can Program detect whether something is being piped to it in this manner, and continue execution instead of blocking if not?

... and is it a good idea to do so?

Answer 1

os.Stdin is treated like a file and has permissions. When os.Stdin is open, the perms are 0600, when closed it's 0620.

This code works:

package main

import (
    "fmt"
    "os"
)

func main() {
    stat, _ := os.Stdin.Stat()
    fmt.Printf("stdin mode: %v
", stat.Mode().Perm())
    if stat.Mode().Perm() == 0600 {
        fmt.Printf("stdin open
")
        return
    }
    fmt.Printf("stdin close
")

}