package main

// filemodify.go - read file, modify it and write it back

/*cat testdata/hello
hello gopher
hello helmut
*/

// inspired by:
// https://pkg.go.dev/io/ioutil#example-ReadFile on 20211228
// and
// https://www.geeksforgeeks.org/strings-replace-function-in-golang-with-examples/

import (
        "fmt"
        "io/ioutil"
        "log"
        "strings"
)

func main() {
        content, err := ioutil.ReadFile("testdata/hello")
        if err != nil {  
                log.Fatal(err)
        }

        //https://yourbasic.org/golang/convert-string-to-byte-slice/
        //s := string([]byte{65, 66, 67, 226, 130, 172})
        contentstring := string(content)

        //strings.Replace(contentstring, "helmut", "hannelore", -1) // -1 replaces all
        contentmodifiedstring := strings.Replace(contentstring, "h", "g", 2)
        //strings.ReplaceAll(contentstring, "h", "g")

        fmt.Printf("File contents:\n%s", contentmodifiedstring)

        //b := []byte("ABC€")
        contentbyte := []byte(contentmodifiedstring)

        //func WriteFile(filename string, data []byte, perm fs.FileMode) error
        errwrite := ioutil.WriteFile("testdata/hellomodified", contentbyte, 0644)
        if err != nil {
                log.Fatal(errwrite)
        }

}