Get Interface Golang Part 2

package main

import (
    "net"
    "fmt"
    "os"
    "strings"
)

// Use the net library to return all Interfaces
// and capture any errors.
func getInterfaces() ([]net.Interface) {
    interfaces, err := net.Interfaces()
    if err != nil {
        panic("Unable to get interfaces.")
    }
    return interfaces
}

// Use the net library to get Interface by Index number
// and capture any errors.
func getInterfaceByIndex(index int) (*net.Interface) {
    inter, err := net.InterfaceByIndex(index)
    if err != nil {
        panic("Unable to get interface by index")
    }
    return inter
}

// Use the net library to get Interface by Name
// and capture any errors
func getInterfaceByName(name string) (*net.Interface) {
    inter, err := net.InterfaceByName(name)
    if err != nil {
        panic("Unable to get interface by name")
    }
    return inter
}

// Using the net library we will loop over all interfaces
// looking for the interface with matching mac_address.
func getInterfaceByHardwareAddress(mac string) (net.Interface) {
    interfaces := getInterfaces()
    for _, inter := range interfaces {
        if strings.ToUpper(mac) == strings.ToUpper(inter.HardwareAddr.String()) {
            return inter
        }
    }
    panic("Unable to find interface with Hardware Address.")
}

func main() {

    args := os.Args
    // If we have only 2 arguments we will assume the
    // second is mac_address.
    if len(args) == 2 {
        mac_address := args[1]
        inter := getInterfaceByHardwareAddress(mac_address)
        fmt.Println(inter.Name)

    // If no arguments were passed in lets just return
    // a list of all interface names and hardware addresses.
    } else if len(args) == 1 {
        for _, inter := range getInterfaces() {
            fmt.Println(inter.Name, inter.HardwareAddr)
        }

    // If the number of command line arguments are not expected
    // lets panic and explain why.
    } else {
        panic("We require one (mac_address) or no command line arguments.")
    }

}

$ go build get_interface.go

$ ./get_interface
lo
en0 12:34:56:68:90:00

$ ./get_interface 12:34:56:68:90:00
en0