Golang compile environment variable into binary - go

Question

If I compile this program
package main
import (
"fmt"
"os"
)
var version = os.Getenv("VERSION")
func main() {
fmt.Println(version)
}
It prints the env var when I run it
VERSION="0.123" ./example
> 0.123
Is there a way to compile the env var into the binary, for example:
VERSION="0.123" go build example.go
Then get the same output when I run
./example

Answer 1

Go 1.5 and above edit:
As of now, the syntax has changed.
On Unix use:
go build -ldflags "-X main.Version=$VERSION"
On Windows use:
go build -ldflags "-X main.Version=%VERSION%"
This is what -X linker flag is for. In your case, you would do
go build -ldflags "-X main.Version $VERSION"
Edit: on Windows this would be
go build -ldflags "-X main.Version %VERSION%"
More info in the linker docs.

Answer 2

Ainer-G's answer led me to the right place, but it wasn't a full code sample answering the question. A couple of changes were required:
Declare the version as var version string
Compile with -X main.version=$VERSION
Here's the full code:
package main
import (
"fmt"
)
var version string
func main() {
fmt.Println(version)
}
Now compile with
go build -ldflags "-X main.version=$VERSION"

Answer 3

There is an os.Setenv() function which you can use to set environment variables.
So you can start your application by setting the environment variable like this:
func init() {
os.Setenv("VERSION", "0.123")
}
If you don't want to do this by "hand", you could create a tool for this which would read the current value of the VERSION environment variable and generate a .go source file in your package containing exactly like the code above (except using the current value of the VERSION environment variable). You can run such code generation by issuing the go generate command.
Read the Generating code blog post for more details about go generate.