main.go

package main

import (
	"bufio"
	"bytes"
	"errors"
	"flag"
	"fmt"
	"log"
	"os"
)

func main() {
	count, err := run()
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(count)
}

func run() (uint64, error) {
	flag.Parse()
	if flag.NArg() < 1 {
		return 0, errors.New("missing file to search")
	} else if flag.NArg() < 2 {
		return 0, errors.New("missing search query")
	}
	fpath, query := flag.Arg(0), []byte(flag.Arg(1))
	file, err := os.Open(fpath)
	if err != nil {
		return 0, err
	}
	scanner := bufio.NewScanner(file)
	count := uint64(0)
	for scanner.Scan() {
		if bytes.Contains(scanner.Bytes(), query) {
			count++
		}
	}
	if err := scanner.Err(); err != nil {
		return 0, err
	}
	return count, nil
}