Porting from ruby to go: find and replace in a file

Question

I am porting some ruby code to golang. I'm having difficulty finding a good equivalent for the below line and wondered if someone knew of a better solution than what I have below. The basic premise is find a line in a file that has a lot of spaces and remove the line.

I also thought of just using exec to call sed -i but when I tried that it didn't work, and the below did finally work.

Ruby:

File.write(filename, File.read(filename).gsub(/^\s*$/,""))

Golang:

b, err := ioutil.ReadFile(filename)
if err != nil {
    return
}

// I happen to know that there will be at least 30 spaces,
// but I would really prefer to not use a hardcoded value here.
// I was just never able to make using '^\s*$' work in the regex.

r := regexp.MustCompile(`[ ]{30,}`)  // there's a space in the []
newb := r.ReplaceAll(b, []byte(""))
err = ioutil.WriteFile(filename, newb, 0666)
if err != nil {
    fmt.Printf("Unable to write to file (%+v)\n", err)
    return
}

Answer 1

Turn on multiline mode, and your original pattern will work:

r := regexp.MustCompile(`(?m)^\s*$`)

Demo using strings: https://play.golang.org/p/6TsfgB83WgX