heredocs.sh

cat > a.go <<EOF
package main

import (
  "fmt"
  "io"
  "os"
)

func main() {
  fmt.Println(os.Args[1:])
  io.Copy(os.Stdout, os.NewFile(3, "fd 3"))
  io.Copy(os.Stdout, os.NewFile(4, "fd 4"))
}
EOF

go run a.go 3<<FD3 4<<FD4 more arguments
This is FD 3
FD3
This is FD 4
FD4