How Can I Check for Available Input on STDIN in Golang?

Checking for Available Input on STDIN in Golang

In certain command-line scenarios, understanding whether input exists on stdin is crucial for tailored behavior. Consider the following example:

package main

import (
    "fmt"
    "io/ioutil"
    "os"
)

func main() {
    bytes, _ := ioutil.ReadAll(os.Stdin)

    if len(bytes) > 0 {
        fmt.Println("Something on STDIN: " + string(bytes))
    } else {
        fmt.Println("Nothing on STDIN")
    }
}

While this code functions for piped input, it halts at ioutil.ReadAll(os.Stdin) when no input is present. This article addresses this issue, providing a solution to determine the availability of stdin data.

Solution: Checking the File Mode

The solution lies in examining the file mode of the stdin stream. When stdin is a regular file (e.g., a terminal), its mode includes os.ModeCharDevice, indicating character device status. Conversely, if input is piped, the mode lacks this flag. The following code demonstrates this approach:

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")
    }
}

With this modification, your program can distinguish between piped and terminal-based stdin inputs, allowing for appropriate behavior adjustments.

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