Cost of string

goregex-byte.go

package main

import (
	"bufio"
	"flag"
	"fmt"
	"log"
	"os"
	"regexp"
	"runtime/pprof"
)

var cpuprofile = flag.String("cpuprofile", "", "write cpu profile to file")

func main() {
	flag.Parse()
	if *cpuprofile != "" {
		f, err := os.Create(*cpuprofile)
		if err != nil {
			log.Fatal(err)
		}
		pprof.StartCPUProfile(f)
		defer pprof.StopCPUProfile()
	}
	file, err := os.Open(flag.Args()[0])
	if err != nil {
		panic(err)
	}
	defer file.Close()

	scanner := bufio.NewScanner(file)
	var i int

	// Compile regular expression first
	r := regexp.MustCompile(`sshd\[\d{5}\]:\s*Failed`)

	for scanner.Scan() {
		line := scanner.Bytes()
		if r.Match(line) {
			i++
		}
	}

	if err := scanner.Err(); err != nil {
		fmt.Println(err)
	}
	fmt.Println(i)
}

goregexp-byte.svg

goregexp-string.go

package main

import (
	"bufio"
	"flag"
	"fmt"
	"log"
	"os"
	"regexp"
	"runtime/pprof"
)

var cpuprofile = flag.String("cpuprofile", "", "write cpu profile to file")

func main() {
	flag.Parse()
	if *cpuprofile != "" {
		f, err := os.Create(*cpuprofile)
		if err != nil {
			log.Fatal(err)
		}
		pprof.StartCPUProfile(f)
		defer pprof.StopCPUProfile()
	}
	file, err := os.Open(flag.Args()[0])
	if err != nil {
		panic(err)
	}
	defer file.Close()

	scanner := bufio.NewScanner(file)
	var i int

	// Compile regular expression first
	r := regexp.MustCompile(`sshd\[\d{5}\]:\s*Failed`)

	for scanner.Scan() {
		line := scanner.Text()
		if r.MatchString(line) {
			i++
		}
	}

	if err := scanner.Err(); err != nil {
		fmt.Println(err)
	}
	fmt.Println(i)
}

goregexp-string.svg