How to run this command via Go?

Question

echo "test_metric:20|c" | nc -v -C -w 1 host.address port

I run this command through terminal, I get the desired result. But how can I do the same via Go code?

I tried this, after going through an answer here-

sh:= os.Getenv("SHELL")
cmd := exec.Command(sh, "-c ", `echo "test_metric:20|c" | nc -v -C -w 1 host.address port`)

cmd.Stdout = os.Stdout

cmd.Run()

But no luck.

You have a trailing space after the `-c` argument. If fixing this does not solve your problem add the Stderr output to the question. — Peter, Jul 21 '20 at 12:38
@Samik : Your approach would fail if the environment variable `SHELL` is not defined, or if it is set to a some shell which does not understand the command syntax or `-c` option. If you write this for POSIX shell, just use a literal `sh` and let it be the responsibility of the caller to ensure that `sh` is in the PATH. — user1934428, Jul 21 '20 at 13:50

score 0 · Answer 1 · answered Jul 23 '20 at 00:50

I do not see the point in calling the shell to do this:

package main

import (
    "bytes"
    "flag"
    "fmt"
    "io"
    "log"
    "net"
    "time"
)

var (
    host    string
    port    int
    timeout string
)

func init() {
    flag.StringVar(&host, "host", "localhost", "host to connect to")
    flag.IntVar(&port, "port", 10000, "port to connect to")
    flag.StringVar(&timeout, "timeout", "1s", "timeout for connection")
}

func main() {
    flag.Parse()

    // Fail early on nonsensical input.
    if port < 1 || port > 65535 {
        log.Fatalf("Illegal port %d: must be >=1 and <=65535", port)
    }

    var (
        // The timeout for the connection including name resolution
        to time.Duration

        // The ubiquitous err
        err error

        // The dial string
        addr = fmt.Sprintf("%s:%d", host, port)

        // The actual connection
        con net.Conn

        // Your playload. It should be easy enough to make this
        // non-static.
        payload = []byte("test_metric:20|c")
    )

    // Check the user has given a proper timeout.
    if to, err = time.ParseDuration(timeout); err != nil {
        log.Fatalf("parsing timeout: %s", err)
    }

    // You might want to implement a retry strategy here.
    // See https://stackoverflow.com/a/62909111/1296707 for details
    if con, err = net.DialTimeout("tcp", addr, to); err != nil {
        log.Fatalf("Error while dialing: %s", err)
    }
    defer con.Close()

    // This simulates about every input.
    // You can use a pipe of a command or whatever you want.
    dummyReader := bytes.NewBuffer(payload)

    if w, err := io.Copy(con, dummyReader); err != nil && w < int64(len(payload)) {
        log.Printf("Short write: written (%d) < payload (%d): %s", w, len(payload), err)
    } else if err != nil {
        // This should not happen, as usually an error is accompanied by a short write
        log.Println("Uuupsie!")
    }

}

Start a netcat listener on one shell:

$ nc -k -l 10000

run the code via

$ go run dacode.go

and you should see your payload on the output of the netcat listener.

In case you want to transfer the output of a program to the remote server, simply call the according command via os.Exec and use io.Copy on con and the io.Reader returned by your command's StdoutPipe().

How to run this command via Go?

1 Answers1