Go: Process multi-line command output and parse

Question

I am trying to extract information from a command line utility, in this case the linux ntpq -c rv command.

Output:

associd=0 status=0638 leap_none, sync_ntp, 3 events, no_sys_peer,
version="ntpd [email protected] Fri Jul 22 17:30:51 UTC 2016 (1)",
processor="x86_64", system="Linux/3.16.0-4-amd64", leap=00, stratum=2,
precision=-22, rootdelay=25.435, rootdisp=49.398, 
refid=8.8.8.8,
reftime=dd64d70e.3edbe503  Thu, Sep 14 2017 12:23:10.245,
clock=dd64dbaa.ded8fa8e  Thu, Sep 14 2017 12:42:50.870, peer=51954,
tc=10, mintc=3, offset=1.941, frequency=3.236, sys_jitter=0.869,
clk_jitter=0.413, clk_wander=0.068

What i need out of this is: stratum and offset.

I have built this piece of code:

if Exists("/usr/bin/ntpq") {
  cmd := exec.Command("ntpq","-c rv")
    cmdReader, err := cmd.StdoutPipe()
    if err != nil {
        fmt.Fprintln(os.Stderr, "Error creating StdoutPipe", err)
        os.Exit(1)
    }
    scanner := bufio.NewScanner(cmdReader)
    go func() {
        for scanner.Scan() {
            fmt.Printf("out %s\n", scanner.Text())
        }
    }()

    err = cmd.Start()
    if err != nil {
        fmt.Fprintln(os.Stderr, "Error starting Cmd", err)
        os.Exit(1)
    }

    err = cmd.Wait()
    if err != nil {
        fmt.Fprintln(os.Stderr, "Error waiting for Cmd", err)
        os.Exit(1)
    }
} 

I am able to get the output from the command, line by line but i am unsure on how to extract only the information i want. Can anyone help me with this?

Answer 1

Use Regular Expression to get the data and parse it into int, and float values.

https://play.golang.org/p/vDx8dw4Mpo

package main

import (
    "fmt"
    "regexp"
    "strconv"
)

func main() {
    // Expected output
    output := `associd=0 status=0638 leap_none, sync_ntp, 3 events, no_sys_peer,
version="ntpd [email protected] Fri Jul 22 17:30:51 UTC 2016 (1)",
processor="x86_64", system="Linux/3.16.0-4-amd64", leap=00, stratum=2,
precision=-22, rootdelay=25.435, rootdisp=49.398, 
refid=8.8.8.8,
reftime=dd64d70e.3edbe503  Thu, Sep 14 2017 12:23:10.245,
clock=dd64dbaa.ded8fa8e  Thu, Sep 14 2017 12:42:50.870, peer=51954,
tc=10, mintc=3, offset=1.941, frequency=3.236, sys_jitter=0.869,
clk_jitter=0.413, clk_wander=0.068`

    // Try to find stratum
    match :=  regexp.MustCompile("stratum=(\\d+),").FindStringSubmatch(output)
    stratum := 0
    if (match != nil) {
        if i, err := strconv.Atoi(match[1]); err == nil {
            stratum = i
        }
    }

    // Try to find offset
    match =  regexp.MustCompile("offset=(\\d+\\.\\d+),").FindStringSubmatch(output)
    offset := 0.0
    if (match != nil) {
        if f, err := strconv.ParseFloat(match[1], 64); err == nil {
            offset = f
        }
    }

    fmt.Println(stratum)
    fmt.Println(offset)
}