How to properly "go build" using exec.Command with many arguments? - go

Question

I'm trying to compile a go package using exec.Command. I was successful with the arguments being "go" and "build" as such below:
package main
import (
"fmt"
"log"
"os/exec"
)
func main() {
out, err := exec.Command("go", "build").Output()
if err != nil {
log.Fatal(err)
}
fmt.Println(out)
}
However, while trying to perform a "go build" with more arguments it seems that I'm doing something wrong? This is what my code looks like:
package main
import (
"fmt"
"log"
"os/exec"
)
func main() {
out, err := exec.Command("set", "GOOS=js&&", "set", "GOARCH=wasm&&", "go", "build", "-o", "C:/Users/Daniel/Desktop/go-workspace/src/sandbox/other/wasm/assets/json.wasm", "kard").Output()
if err != nil {
log.Fatal(err)
}
fmt.Println(out)
}
The output is exec: "set": executable file not found in %PATH%
The normal command I would perform for this in the command line would be set GOOS=js&& set GOARCH=wasm&& go build -o C:\Users\Daniel\Desktop\go-workspace\src\sandbox\other\wasm\assets\json.wasm kard.
I assume there is something I'm misunderstanding with using exec.Command? I really appreciate any support.

Answer 1

The application uses shell syntax to set the environment variables, but the exec package does not use a shell (unless the command that you are running is a shell).
Use the command environment to specify the environment variables for the exec'ed command.
The go build does not normally write to stdout, but it does write errors to stderr. Use CombinedOutput instead of Output to easily capture error text.
cmd := exec.Command("go", "build", "-o", "C:/Users/Daniel/Desktop/go-workspace/src/sandbox/other/wasm/assets/json.wasm", "kard")
cmd.Env = []string{"GOOS=js", "GOARCH=wasm"}
out, err := cmd.CombinedOutput()
if err != nil {
fmt.Printf("%v: %s\n", err, out)
}