How to Read an Entire File into a String in Go?

Reading an Entire File into a String Variable in Go

In Go, you can encounter situations where you want to read the contents of a small file into a string variable for efficient processing, without iterating through the file line by line. Fortunately, the Go ecosystem offers a convenient solution to this task.

Solution Using io.ReadFile

For reading a whole file into a string variable, Go provides the io.ReadFile function from the io package. The syntax of io.ReadFile is as follows:

func ReadFile(filename string) ([]byte, error)

io.ReadFile takes a single argument, filename, which represents the path to the file you want to read. It returns two values: a byte slice ([]byte) containing the contents of the file and an error value (error).

Conversion to String

By default, io.ReadFile returns a byte slice, but you might want to convert it into a string. You can achieve this using the following code:

s := string(buf)

Here, buf is the byte slice returned by io.ReadFile.

Example Usage

Here's an example that demonstrates how to use io.ReadFile to read a whole file into a string:

package main

import (
    "fmt"
    "io/ioutil"
)

func main() {
    filename := "test.txt"
    buf, err := ioutil.ReadFile(filename)
    if err != nil {
        fmt.Println("Could not read file:", err)
        return
    }

    str := string(buf)
    fmt.Println("File contents:")
    fmt.Println(str)
}

This code reads the contents of the test.txt file into a byte slice and converts it to a string. The string is then printed to the console.

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