How to Efficiently Read a Single Line from a Text File into a String in Go?

Reading a String from a Text File in Go

When working with text files in Go, it may be desirable to read a line of text into a string. While the standard library provides low-level functions that return byte arrays, a more convenient way is to use specialized functions that handle this task directly.

Solution

The following code demonstrates how to read a single line from a text file into a string:

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

// ReadLine reads a single line from a file.
func ReadLine(r *bufio.Reader) (string, error) {
    var (
        isPrefix bool = true
        err       error
        line, ln  []byte
    )

    for isPrefix && err == nil {
        line, isPrefix, err = r.ReadLine()
        ln = append(ln, line...)
    }

    return string(ln), err
}

func main() {
    fi := `<path-to-your-file>`
    f, err := os.Open(fi)
    if err != nil {
        fmt.Println("error opening file= ", err)
        os.Exit(1)
    }
    defer f.Close()

    r := bufio.NewReader(f)
    s, e := ReadLine(r)
    for e == nil {
        fmt.Println(s)
        s, e = ReadLine(r)
    }
}

This code opens the specified file, initializes a buffered reader, and calls the ReadLine function to read each line from the file. The resulting string is printed to stdout.

Usage

Call the ReadLine function on a buffer reader to get the contents of a single line as a string. The ReadLine function handles reading multiple lines if newline characters are not present in the input.

This approach eliminates the need to handle byte arrays and convert them to strings manually, providing a simple and efficient way to read line-oriented text files.

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