Is My Go Command Receiving Data from a Pipe?

How to Determine if a Command is Piped in Go?

When working with input and output in Go, it's often necessary to determine if a command is being piped or not. Piping allows data to be passed from the output of one process to the input of another via a Unix pipe.

For instance:

<code class="sh">cat test.txt | mygocommand # Piped
mygocommand # Not piped</code>

This distinction can be important for customizing your application's behavior.

Solution

Go provides a way to check if stdin is piped by using os.Stdin.Stat(). Here's an example:

<code class="go">package main

import (
    "fmt"
    "os"
)

func main() {
    fi, _ := os.Stdin.Stat()

    if (fi.Mode() & os.ModeCharDevice) == 0 {
        fmt.Println("data is from pipe")
    } else {
        fmt.Println("data is from terminal")
    }
}</code>

When the command is piped (as in the first example), the output will be:

data is from pipe

Otherwise, it will be:

data is from terminal

How it works

The os.Stdin.Stat() function returns a FileInfo object containing information about the stdin file descriptor. The Mode() method of FileInfo returns a file mode that includes information about the type of file. If the returned mode includes the os.ModeCharDevice flag, it indicates that the file is a character device, such as a terminal. If it does not, it indicates that the file is a regular file or a pipe.

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