GO language: Reading a file and turning the content into an array

Question

I want to implement this array in main function above but how?

hosts := []string{"[email protected]", "[email protected]"}

Content of JSON file:

inanzzz@inanzzz-VirtualBox:~/go$ go run reader.go < hosts.txt 
{
   {
      "username":"inanzzz1",
      "ip":"100.79.154.22"
   },
   {
      "username":"inanzzz2",
      "ip":"200.79.190.11"
   }
}

GO file which reads the JSON file above:

package main

import (
    "os"
    "bufio"
    "fmt"
)

func main() {
    r := bufio.NewReader(os.Stdin)
    line, err := r.ReadString('\n')
    for i := 1; err == nil; i++ {
        //fmt.Printf("Line %d: %s", i, line)
        fmt.Printf(line)
        line, err = r.ReadString('\n')
    }
}

Franchu · Accepted Answer · 2014-11-13 20:27:28Z

2

Assuming that what you have is a json array (first and last {} replaced by []) instead of the invalid JSON described in hosts.txt here you have a working solution:

package main

import (
    "encoding/json"
    "fmt"
    "os"
)

type UsernameIp struct {
    Username string `json:"username"`
    Ip       string `json:"ip"`
}

func main() {
    j := json.NewDecoder(os.Stdin)
    var src []UsernameIp
    j.Decode(&src)

    var hosts []string
    for _, h := range src {
        entry := fmt.Sprintf("%s@%s", h.Username, h.Ip)
        hosts = append(hosts, entry)
    }

    fmt.Println(hosts)
}

Correct hosts.txt file:

[
   {
      "username":"inanzzz1",
      "ip":"100.79.154.22"
   },
   {
      "username":"inanzzz2",
      "ip":"200.79.190.11"
   }
]

edited Nov 13, 2014 at 20:27

answered Nov 13, 2014 at 20:17

Franchu

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2 Comments

BentCoder Over a year ago

When I run it with go run json.go < hosts.txt I get [] as result

Franchu Over a year ago

You need to have a valid JSON file. If you pass the file you suggested as an example in through a linter you will see it is not valid. A JSON array starts and ends with []

Alex Gitelman · Accepted Answer · 2014-11-13 21:56:30Z

1

You probably should unmarshall json first and then iterate over result. First - make hosts.txt a valid JSON. For that use [] instead of {}:

[
   {
      "username":"inanzzz1",
      "ip":"100.79.154.22"
   },
   {
      "username":"inanzzz2",
      "ip":"200.79.190.11"
   }
]

Then unmarshall.

Here is full example:

package main

import ( "fmt" "encoding/json"
)

func main() {

  type host struct {
   Username string 
   Ip string  
}

cont := `    [
   {
      "username":"inanzzz1",
      "ip":"100.79.154.22"
   },
   {
      "username":"inanzzz2",
      "ip":"200.79.190.11"
   }
]
 `


// Read file to some byte array. We will use string for this example.
var arr []host
err := json.Unmarshal([]byte(cont), &arr) 
if err != nil {   
    fmt.Println(err)
} 

hosts := make([]string, len(arr))
for i, h := range arr {
   hosts[i] = h.Username + "@" + h.Ip
} 
fmt.Println(hosts)

}

edited Nov 13, 2014 at 21:56

answered Nov 13, 2014 at 20:14

Alex Gitelman

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1 Comment

BentCoder Over a year ago

I'm trying to remove your hard coded JSON variable and implement "reading a txt file" feature instead. So how should I modify your code. I'm running it with go run json.go < hosts.txt

DiBa · Accepted Answer · 2014-11-13 20:09:58Z

You can use ioutil.ReadFile to read the whole file as a string which is a json document and then Unmarshal the string into a struct that you will have made for easy access:

type user_ip struct{
    username string `json:"username"`
    ip string       `json:"ip"`
}

type jsonStruct struct{
    sample []user_ip
}


func main() {

    //you'll have to read file here
    str := `{
               {
                  "username":"inanzzz1",
                  "ip":"100.79.154.22"
               },
               {
                  "username":"inanzzz2",
                  "ip":"200.79.190.11"
               }
            }`

    userIP := jsonStruct{}

    err := json.Unmarshal(str, &userIP)
    panic(err)

    //do what you want with the struct here
}

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