How Can I Efficiently Read an Entire File into a String in Go?

Reading Entire Files into Strings in Go

When handling numerous small files, reading each line individually can be inefficient. Go provides a convenient function to facilitate reading an entire file into a single string variable.

Solution Using the Deprecated ioutil Package:

The outdated ioutil package contains a function called ReadFile that enables file reading into a byte slice:

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

Note that this function returns a byte slice, which must be converted to a string if desired:

s := string(buf)

Solution Using the io Package (Preferred for New Code):

The io package offers a modern and preferred alternative to ioutil.ReadFile:

func ReadAll(r io.Reader) ([]byte, error)

This function requires an io.Reader as input, which a file can be easily adapted to using os.Open:

file, err := os.Open(filename)
if err != nil {
    // Handle error
}
data, err := io.ReadAll(file)
if err != nil {
    // Handle error
}

The resulting byte slice can again be converted to a string if necessary.

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