go readline -> string

What is the idiomatic way to do a readline to string in Go? the raw functions provided in the standard library seem really low level, they return byte arrays. Is there any built in easier way to get a string out of a readline function?

I wrote up a way to easily read each line from a file. The Readln(*bufio.Reader) function returns a line (sans \n) from the underlying bufio.Reader struct.

// Readln returns a single line (without the ending \n)
// from the input buffered reader.
// An error is returned iff there is an error with the
// buffered reader.
func Readln(r *bufio.Reader) (string, error) {
  var (isPrefix bool = true
       err error = nil
       line, ln []byte
      )
  for isPrefix && err == nil {
      line, isPrefix, err = r.ReadLine()
      ln = append(ln, line...)
  }
  return string(ln),err
}

You can use Readln to read every line from a file. The following code reads every line in a file and outputs each line to stdout.

f, err := os.Open(fi)
if err != nil {
    fmt.Println("error opening file= ",err)
    os.Exit(1)
}
r := bufio.NewReader(f)
s, e := Readln(r)
for e == nil {
    fmt.Println(s)
    s,e = Readln(r)
}

Cheers!

Here's are some examples using bufio.ReadLine and bufio.ReadString.

 package main

import (
	"bufio"
	"fmt"
	"os"
)

func ReadLine(filename string) {
	f, err := os.Open(filename)
	if err != nil {
		fmt.Println(err)
		return
	}
	defer f.Close()
	r := bufio.NewReaderSize(f, 4*1024)
	line, isPrefix, err := r.ReadLine()
	for err == nil && !isPrefix {
		s := string(line)
		fmt.Println(s)
		line, isPrefix, err = r.ReadLine()
	}
	if isPrefix {
		fmt.Println("buffer size to small")
		return
	}
	if err != io.EOF {
		fmt.Println(err)
		return
	}
}

func ReadString(filename string) {
	f, err := os.Open(filename)
	if err != nil {
		fmt.Println(err)
		return
	}
	defer f.Close()
	r := bufio.NewReader(f)
	line, err := r.ReadString('\n')
	for err == nil {
		fmt.Print(line)
		line, err = r.ReadString('\n')
	}
	if err != io.EOF {
		fmt.Println(err)
		return
	}
}

func main() {
	filename := `testfile`
	ReadLine(filename)
	ReadString(filename)
}

You can also use bufio.NewScanner:

package main

import (
   "bufio"
   "os"
)

func main() {
   f, e := os.Open("file.txt")
   if e != nil {
      panic(e)
   }
   defer f.Close()
   s := bufio.NewScanner(f)
   for s.Scan() {
      println(s.Text())
   }
}

https://pkg.go.dev/bufio#Scanner