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Go Embedded Files

Embedded files are files whose contents the compiler packs into the program at build time. A //go:embed line above a variable names the file that fills it.

Embedding a greeting

The //go:embed line names hello.txt. The string variable greeting starts with the text from that file.

package main

import (
	_ "embed"
	"fmt"
)

//go:embed hello.txt
var greeting string

func main() {
	fmt.Print(greeting)
}

Embedding as bytes

The same line above a byte slice stores the file as bytes. The length shows the byte count, and the text prints after it.

package main

import (
	_ "embed"
	"fmt"
)

//go:embed banner.txt
var banner []byte

func main() {
	fmt.Println(len(banner))
	fmt.Print(string(banner))
}

Choosing between two files

Two variables hold two embedded files. A stored number picks which text prints.

package main

import (
	_ "embed"
	"fmt"
)

//go:embed one.txt
var first string

//go:embed two.txt
var second string

func main() {
	pick := 2
	if pick == 1 {
		fmt.Print(first)
	} else {
		fmt.Print(second)
	}
}

Example

package main

import (
	_ "embed"
	"fmt"
)

//go:embed appetizer.txt
var appetizer string

//go:embed dessert.txt
var dessert string

func main() {
	fmt.Println("Menu:")
	fmt.Print(appetizer)
	fmt.Print(dessert)
}

Key points

  • The //go:embed line sits directly above the variable it fills.
  • An embedded file can fill a string variable or a byte slice variable.
  • The named file must sit beside the source file when the program builds.
  • The contents are fixed at build time, so a running program never opens the file.

In this example, two short files are embedded as strings. Main prints a menu heading first. It then prints the two notes one after the other.

Note

Changing an embedded file means building the program again, because the old build holds the old contents.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Go Playground

Exercise

When does the content of an embedded file enter the program?