How Can I Detect Readable Content on STDIN in Go Without Blocking?

Detecting Readable Content on STDIN in Go

Suppose you want a command-line tool to behave differently based on the presence of input on STDIN. However, using ioutil.ReadAll(os.Stdin) directly may lead to unexpected behavior.

In particular, if the tool is called without any STDIN input, the program will indefinitely wait for an input, preventing it from proceeding further.

Solution

To solve this issue, you can utilize os.Stdin.Stat() to check if the STDIN file descriptor is a character device. The following code snippet demonstrates how to achieve this:

package main

import (
    "fmt"
    "os"
)

func main() {
    stat, _ := os.Stdin.Stat()
    if (stat.Mode() & os.ModeCharDevice) == 0 {
        fmt.Println("data is being piped to stdin")
    } else {
        fmt.Println("stdin is from a terminal")
    }
}

When ModeCharDevice flag is cleared for the STDIN file, it indicates that data is being piped to the STDIN. Otherwise, it suggests that STDIN is connected to a terminal. By checking this flag, you can determine whether or not there is something to read on STDIN without blocking the program.

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