using curl with commands in go - linux

Question

I'm using Go with command to execute curl which works as expected
curl := exec.Command("curl", "https://services.odata.org/V3/northwind/northwind.svc/")
out, err := curl.Output()
if err != nil {
fmt.Println("erorr" , err)
return
}
fmt.Println(out)
Now I want to use some placeholders like
curl -O http://quiet-waters-1228.herokuapp.com/assets/image.jpg
but now I need to get the url for command
e.g. if I run in bash mytool url I got the url value
`curl -O $(mytool url)`
The problem is that we need to execute the command in the code and I'm not sure how to pass it
curl := exec.Command("curl", "curl -O $(url)")
out, err := curl.Output()
if err != nil {
fmt.Println("erorr" , err)
return
}
fmt.Println(out)

Answer 1

In os package you have slice of strings which contains all arguments passed by shell to your program.
os.Args 0th value, i.e., first element is going to be name of the command itself.
If your tool command is mytool, os.Args[0] contains mytool.
Rest are going to be the arguments, which are passed by shell.
package main
import (
"log"
"os"
"os/exec"
)
func main() {
if len(os.Args) < 2 {
// If argument is not provided quit
log.Fatalln("url not provided")
}
url := os.Args[1] // URL
cmd := exec.Command("curl", "-O", url)
cmd.Run()
}
You can also download multiple URLs concurrently,
var wg *sync.WaitGroup
func main() {
urls := os.Args[1:]
wg = new(sync.WaitGroup)
wg.Add(len(urls))
for _, url := range urls {
go download(url)
}
wg.Wait()
}
func download(url string) {
defer wg.Done()
cmd := exec.Command("curl", "-O", url)
cmd.Run()
}