Golang : How to get Unix file descriptor for console and file

A short tutorial showing you how to obtain the Unix file descriptor for terminal/console and file in Golang with the os package. Basically, there are 3 file descriptors under Unix/Linux environment :

• 0 for input
• 1 for output
• 3 for file

and knowing this information can be helpful in situation when you want to test if a given variable is a file or console.

Here we go!

 package main

 import (
 "fmt"
 "os"
 )

 func main() {

 // get console unix file descriptor
 outputFileDesc := int(os.Stdout.Fd())
 outputName := os.Stdout.Name()
 fmt.Println("Terminal or console output Unix file descriptor : ", outputFileDesc)
 fmt.Println("output Unix file descriptor name : ", outputName)

 fmt.Println("------------------------")

 inputFileDesc := int(os.Stdin.Fd())
 inputName := os.Stdin.Name()
 fmt.Println("Terminal or console input Unix file descriptor : ", inputFileDesc)
 fmt.Println("input Unix file descriptor name : ", inputName)

 fmt.Println("------------------------")
 // get a file unix file descriptor
 file, err := os.Open("file.data")

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 fileDescriptor := int(file.Fd())  // get the unix descriptor
 fileDescriptorName := file.Name() // get the file name

 file.Close()

 fmt.Printf("%s Unix file descriptor : %d \n", fileDescriptorName, fileDescriptor)

 }

Output :

Terminal or console output Unix file descriptor : 1

output Unix file descriptor name : /dev/stdout

------------------------

Terminal or console input Unix file descriptor : 0

input Unix file descriptor name : /dev/stdin

------------------------

file.data Unix file descriptor : 3

Happy coding!

References :

https://golang.org/pkg/os/#File.Fd

https://socketloop.com/references/golang-os-file-fd-function-example

http://www.theunixschool.com/2010/08/unix-file-descriptors.html