How to Redirect Input to `exec.Command()` in Go?

Running Commands with Input Redirection Using exec.Command()

In Go, exec.Command() offers a convenient way to execute external commands. However, handling input redirection can be challenging. This discussion explores how to use exec.Command() to run the command /sbin/iptables-restore < /etc/iptables.conf.

Initially, attempts to set up the command with < and < /etc/iptables.conf failed. Piping the file name through stdin also didn't work. Instead, to redirect input to stdin, it's necessary to first read the contents of the input file, /etc/iptables.conf.

Here's how to accomplish this:

package main

import (
    "io"
    "io/ioutil"
    "log"
    "os/exec"
)

func main() {
    bytes, err := ioutil.ReadFile("/etc/iptables.conf")
    if err != nil {
        log.Fatal(err)
    }
    cmd := exec.Command("/sbin/iptables-restore")
    stdin, err := cmd.StdinPipe()
    if err != nil {
        log.Fatal(err)
    }
    err = cmd.Start()
    if err != nil {
        log.Fatal(err)
    }
    _, err = io.WriteString(stdin, string(bytes))
    if err != nil {
        log.Fatal(err)
    }
}

This approach allows us to read the file's content, pipe it to the command's stdin, and then start the command with the desired input redirection.

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