Issues with io/ioutil

Question

Good afternoon,

I'm trying to grab processes id's with my limited knowledge on golang and the below is what I've come up with:

    package main

import (
    "fmt"
    "io/ioutil"
    "log"
    "os"
    "os/exec"
    "strings"
)

func main() {
    cmd := exec.Command("tasklist.exe")
    out, err := cmd.CombinedOutput()
    if err != nil {
        log.Fatal(err)
    }
    f, err := os.Create("data.txt")

    if err != nil {
        log.Fatal(err)
    }

    defer f.Close()

    val := out
    data := []byte(val)

    _, err2 := f.Write(data)

    if err2 != nil {
        log.Fatal(err2)
    }

    val2 := " and red fox\n"
    data2 := []byte(val2)

    var idx int64 = int64(len(data))

    _, err3 := f.WriteAt(data2, idx)

    if err3 != nil {
        log.Fatal(err3)
    }

    fmt.Println("done")
    /* ioutil.ReadFile returns []byte, error */
    explorer, err := ioutil.ReadFile("data.txt")
    /* ... omitted error check..and please add ... */
    /* find index of newline */
    file := string(data)
    line := 0
    /* func Split(s, sep string) []string */
    temp := strings.Split(file, "\n")

    for _, item := range temp {
        fmt.Println("[", line, "]\t", item)
        line++
    }
    fmt.Println(explorer)
}

My Main issue is that i keep running into the same wall where ioutil won't let me assign a value before reading the file.

Is anyone able to help me out here?

Answer 1

I don't know what's not working in your original example, but a few minutes of experimentation and reading the docs for tasklist.exe gave me something better. The main improvement is letting tasklist.exe do the heavy lifting by giving it args.

package main

import (
    "bytes"
    "encoding/csv"
    "fmt"
    "log"
    "os/exec"
)

func main() {
    // original command:
    // tasklist.exe /nh /fo csv /fi "IMAGENAME eq explorer.exe"
    // /nh = no header
    // /fo csv = format output to csv
    // /fi = filter on query
    //
    // run tasklist.exe /? for more info
    //
    // sample output:
    // "explorer.exe","4860","Console","1","102,240 K"

    // start tasklist with args to do the hard work for us.
    // we want CSV output (easier to parse), and let tasklist search for explorer.exe.
    // obviously you could seach for another task name instead of explorer.exe.
    //
    // the key thing here is that the query ("IMAGENAME ...") doesn't
    // require " when passed as an arg because exec.Command()
    // will apparently handle that for you 
    // (quoting like `"IMAGENAME..."` produced an error from Output() )
    cmd := exec.Command("tasklist.exe", "/nh", "/fo", "csv", "/fi", "IMAGENAME eq explorer.exe")
    out, err := cmd.Output()
    if err != nil {
        log.Fatalln(err)
    }

    // create a csv reader around the output of the above command.
    // then use ReadAll() to split the csv into [][]string.. a slice
    // of "lines" (aka records, rows) where each line is a slice of 
    // csv "columns" (aka fields, entries).
    r := csv.NewReader(bytes.NewReader(out))
    lines, err := r.ReadAll()
    if err != nil {
        log.Fatalln(err)
    }

    // the result may have multiple processes (eg svchost.exe) or none.
    for _, line := range lines {
        // the process id is at index 1 as a string.
        // do whatever you need to do with the result.
        fmt.Println(line[1])
    }
}