script to run sed into some files, written in go, for learning purposes

sed1.go

package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
)

type sed struct {
	rulesFilename string
	dir           string

	rules map[string]string
	files []string
}

func (s *sed) loadRules() error {
	f, err := os.Open(s.rulesFilename)
	if err != nil {
		return err
	}
	defer f.Close()

	s.rules = make(map[string]string)

	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		tmp := strings.Split(scanner.Text(), "=")
		s.rules[tmp[0]] = tmp[1]
	}
	return scanner.Err()
}

func (s *sed) loadFiles() error {
	s.files = []string{}
	err := filepath.Walk(s.dir, func(path string, f os.FileInfo, err error) error {
		if !f.IsDir() && strings.HasSuffix(path, ".json") && !strings.Contains(path, "datavirt") {
			s.files = append(s.files, path)
		}
		return nil
	})

	return err
}

func (s *sed) apply() error {
	err := s.loadRules()
	if err != nil {
		return err
	}

	err = s.loadFiles()
	if err != nil {
		return err
	}

	return s.runSed()
}

func (s *sed) runSed() error {
	for _, file := range s.files {
		for name, display := range s.rules {
			args := fmt.Sprintf(`s|"name": "%s",|"name": "%s",\n            "displayName": "%s",|`, name, name, display)
			out, err := exec.Command("/usr/bin/sed", "-i", args, file).Output()
			if err != nil {
				if ee, ok := err.(*exec.ExitError); ok {
					fmt.Printf("error executing command.\nstdout: %s\nstderr: %s\n", out, ee.Stderr)
				}
				return err
			}
		}
	}

	return nil
}

func main() {
	if len(os.Args) == 1 {
		log.Fatalf("Usage: %s <rules-file> [dir]", os.Args[0])
	}

	var dir string
	if len(os.Args) > 2 {
		dir = os.Args[2]
	} else {
		cwd, err := os.Getwd()
		if err != nil {
			log.Fatalf("Error: %s", err)
		}
		dir = cwd
	}

	s := &sed{rulesFilename: os.Args[1], dir: dir}
	if err := s.apply(); err != nil {
		log.Fatalf("Error: %s", err)
	}
}