Embed Directive

//go:embed is a compiler directive that allows programs to include arbitrary files and folders in the Go binary at build time. Read more about the embed directive in the embed package documentation.

package main

Import the embed package; if you don't use any exported identifiers from this package, you can do a blank import with _ "embed".

import (
	"embed"
	"fmt"
	"io/fs"
)

embed directives accept paths relative to the directory containing the Go source file. This directive embeds the contents of the file into the string variable immediately following it.

//go:embed folder/single_file.txt
var fileString string

Or embed the contents of the file into a []byte.

//go:embed folder/single_file.txt
var fileByte []byte

We can also embed multiple files or even folders with wildcards. This uses a variable of the embed.FS type, which implements a simple virtual file system.

//go:embed folder/single_file.txt
//go:embed folder/*.hash
var folder embed.FS

func main() {

Print out the contents of single_file.txt.

	fmt.Print(fileString)
	fmt.Print(string(fileByte))

Retrieve some files from the embedded folder.

	content1, _ := folder.ReadFile("folder/file1.hash")
	fmt.Print(string(content1))

	content2, _ := folder.ReadFile("folder/file2.hash")
	fmt.Print(string(content2))

embed.FS implements fs.FS, so the io/fs helpers work on it.

	fs.WalkDir(folder, ".", func(path string, d fs.DirEntry, err error) error {
		fmt.Println("embedded:", path)
		return err
	})
}

$ go run ./76_embed_directive
hello go
hello go
123
456
embedded: .
embedded: folder
embedded: folder/file1.hash
embedded: folder/file2.hash
embedded: folder/single_file.txt

76_embed_directive/folder/file1.hash

76_embed_directive/folder/file2.hash

76_embed_directive/folder/single_file.txt

hello go

View on GitHub