contract_bytecode.go

package main

import (
	"context"
	"encoding/hex"
	"fmt"
	"log"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/ethclient"
)

func main() {
	client, err := ethclient.Dial("https://rinkeby.infura.io")
	if err != nil {
		log.Fatal(err)
	}

	contractAddress := common.HexToAddress("0x147B8eb97fD247D06C4006D269c90C1908Fb5D54")
	bytecode, err := client.CodeAt(context.Background(), contractAddress, nil) // nil is latest block
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(hex.EncodeToString(bytecode)) // 60806...10029
}