You can use this to count all the lines in a directory

line_counter.go

package main

import (
	"bytes"
	"fmt"
	"io"
	"log"
	"math/big"
	"os"
	"path/filepath"
	"runtime"
)

func main() {
	var filePath string
	//Should support huge numbers
	lineCount := big.NewInt(0)
	if len(os.Args) <= 1 {
		fmt.Println("Need a directory to count. Ex: ./counter ./dir")
		os.Exit(-1)
	}
	filePath = os.Args[1]
	err := filepath.Walk(filePath,
		func(path string, info os.FileInfo, err error) error {
			fmt.Println("Visiting: "+ path)
			if err != nil {
				return err
			}

			f, err := os.Open(path)
			if err != nil {
				return err
			}
			i, err := lineCounter(f)
			lineCount = lineCount.Add(lineCount, big.NewInt(int64(i)))
			return nil
		})
	if err != nil {
		log.Println(err)
	}
	fmt.Println("Total Lines: "+ lineCount.String())
}

func lineCounter(r io.Reader) (int, error) {
	buf := make([]byte, 32*1024)
	count := 0
	var lineSep []byte
	if runtime.GOOS == "windows"{
		lineSep = []byte{'\r','\n'}
	} else {
		lineSep = []byte{'\n'}
	}

	for {
		c, err := r.Read(buf)
		count += bytes.Count(buf[:c], lineSep)

		switch {
		case err == io.EOF:
			return count, nil

		case err != nil:
			return count, err
		}
	}
}

To compile (windows):

go build -o counter.exe

To compile (non-windows):

go build -o counter

To use (windows):

.\counter.exe .\dir

To use (non-windows):

./counter ./dir