Golang 1.8 - Windows - Find, replace output modified files in directory *Learning Project, in progress*

gistfile1.txt

package main

import (
	"bytes"
	"fmt"
	"io/ioutil"
	"os"
	"path/filepath"
	"time"
)

func main() {
	t := time.Now()

	if len(os.Args) > 5 {
		fmt.Println("\n")
		fmt.Println("Too many arguments\n")
		fmt.Println("-------------------------------------------------------------------------------\n")
		fmt.Println("   FAR                ::     Find and Replace for Windows\n")
		fmt.Println("-------------------------------------------------------------------------------\n")

		fmt.Println("  Started : ", t.Local())
		fmt.Println("\n")

		fmt.Printf("       Required Usage :: FAR file_extension output_prefix ")
		fmt.Printf("%#v", "search text")
		fmt.Printf(" ")
		fmt.Printf("%#v\n", "replace text")
		fmt.Println("\n")

		fmt.Println("       file_extension :: the file extension of files to search for. Example: .txt")
		fmt.Println("        output_prefix :: the prefix appended to all modified files. Example: mod_")
		fmt.Printf("       ")
		fmt.Printf("%#v", "search text")
		fmt.Printf("  ")
		fmt.Println(":: The 'find' text. Use quotes for phrases.")
		fmt.Printf("       ")
		fmt.Printf("%#v", "replace text")
		fmt.Printf(" ")
		fmt.Println(":: The 'replace' with text. Use quotes for phrases.")

		fmt.Println("-------------------------------------------------------------------------------\n")
		os.Exit(1)
	}

	if len(os.Args) < 5 {
		fmt.Println("\n")
		fmt.Println("Too few arguments\n")
		fmt.Println("-------------------------------------------------------------------------------\n")
		fmt.Println("   FAR                ::     Find and Replace for Windows\n")
		fmt.Println("-------------------------------------------------------------------------------\n")

		fmt.Println("  Started : ", t.Local())
		fmt.Println("\n")

		fmt.Printf("       Required Usage :: FAR file_extension output_prefix ")
		fmt.Printf("%#v", "search text")
		fmt.Printf(" ")
		fmt.Printf("%#v\n", "replace text")
		fmt.Println("\n")

		fmt.Println("       file_extension :: the file extension of files to search for. Example: .txt")
		fmt.Println("        output_prefix :: the prefix appended to all modified files. Example: mod_")
		fmt.Printf("       ")
		fmt.Printf("%#v", "search text")
		fmt.Printf("  ")
		fmt.Println(":: The 'find' text. Use quotes for phrases.")
		fmt.Printf("       ")
		fmt.Printf("%#v", "replace text")
		fmt.Printf(" ")
		fmt.Println(":: The 'replace' with text. Use quotes for phrases.")

		fmt.Println("-------------------------------------------------------------------------------\n")
		os.Exit(1)
	}

	fileExtension := os.Args[1]
	fileOutputMod := os.Args[2]
	textInput := os.Args[3]
	textOutput := os.Args[4]

	i := -1

	dirname := "." + string(filepath.Separator)
	d, err := os.Open(dirname)
	if err != nil {
		fmt.Println(err)
	}

	defer d.Close()

	files, err := d.Readdir(-1)
	if err != nil {
		fmt.Println(err)
	}

	fileList := make([]string, 0)
	for _, file := range files {

		if file.Mode().IsRegular() {

			if filepath.Ext(file.Name()) == fileExtension {
				i++
				fileList = append(fileList, file.Name())
			}
		}
	}

	fmt.Println("\n")
	fmt.Println(i+1, "files detected")

	for j := 0; j < i+1; j++ {
		eachFile := (fileList[j])

		input, err := ioutil.ReadFile(eachFile)
		if err != nil {
			fmt.Println(err)
		}

		output := bytes.Replace(input, []byte(textInput), []byte(textOutput), -1)

		eachFileOut := eachFile
		modFileOut := fileOutputMod + eachFileOut
		if err = ioutil.WriteFile(modFileOut, output, 0666); err != nil {
			fmt.Println(err)
		}
	}
}