Go 每日一庫之 jj

darjun發表於2020-03-26
Go

簡介

在前面兩篇文章中，我們分別介紹了快速讀取 JSON 值的庫gjson和快速設定 JSON 值的庫sjson。今天我們介紹它們的作者tidwall的一個基於gjson和sjson的非常實用的命令列工具jj。它是使用 Go 編寫的快速讀取和設定 JSON 值的命令列程式。

快速使用

Mac 上可以直接使用brew install tidwall/jj/jj安裝。其他系統可以通過下載編譯好的可執行程式，下載地址為github.com/tidwall/jj/…。

我選擇使用go get安裝：

$ go get github.com/tidwall/jj/cmd/jj
複製程式碼

上面命令執行完成之後，編譯生成的jj程式會放在$GOPATH/bin目錄中，我習慣把$GOPATH/bin加入系統可執行目錄$PATH中，故可以直接使用。

簡單的讀取和設定（我的環境為 Win10 + Git Bash）：

$ echo '{"name":{"first":"li","last":"dj"}}' | jj name.last
dj

$ echo '{"name":{"first":"li","last":"dj"}}' | jj -v dajun name.last
{"name":{"first":"li","last":"dajun"}}
複製程式碼

通過鍵路徑來指定讀取/設定的位置，上面第一個命令讀取欄位name.last，返回dj。

-v選項指定設定的值。第二個命令將欄位name.last設定為dajun，輸出設定之後的 JSON 串。鍵路徑在前兩篇文章中有詳細的介紹，不熟悉的可以回去看一下。

讀取和設定

實際上讀取和設定的語法和形式與我們前面介紹gjson和sjson提到的基本一樣，只不過是在命令列上完成的而已。

讀取不存在的欄位，返回null：

$ echo '{"name":{"first":"li","last":"dj"}}' | jj name.middle
null
複製程式碼

讀取一個物件型別的欄位，返回該物件的 JSON 表示：

$ echo '{"name":{"first":"li","last":"dj"}}' | jj name
{"first":"li","last":"dj"}
複製程式碼

使用索引（從 0 開始）讀取陣列的元素，非法的索引將返回空：

$ echo '{"fruits":["apple","orange","banana"]}' | jj fruits.1
orange

$ echo '{"fruits":["apple","orange","banana"]}' | jj fruits.3

複製程式碼

使用索引設定陣列的元素，下面命令將陣列fruits的第二個元素設定為pear：

$ echo '{"fruits":["apple","orange","banana"]}' | jj -v pear fruits.1
{"fruits":["apple","pear","banana"]}
複製程式碼

使用-1或陣列長度作為索引，可以在陣列後新增一個元素。如果索引超過了陣列長度，則會多一定數量的null：

$ echo '{"fruits":["apple","orange","banana"]}' | jj -v strawberry fruits.-1
{"fruits":["apple","orange","banana","strawberry"]}

$ echo '{"fruits":["apple","orange","banana"]}' | jj -v grape fruits.3
{"fruits":["apple","orange","banana","grape"]}

$ echo '{"fruits":["apple","orange","banana"]}' | jj -v watermelon fruits.5
{"fruits":["apple","orange","banana",null,null,"watermelon"]}
複製程式碼

使用選項-D刪除指定鍵路徑上的元素，如果對應元素不存在，則無效果：

$ echo '{"name":"dj","age":18}' | jj -D age
{"name":"dj"}

$ echo '{"fruits":["apple","orange","banana"]}' | jj -D fruits.2
{"fruits":["apple","orange"]}

$ echo '{"fruits":["apple","orange","banana"]}' | jj -D fruits.5
{"fruits":["apple","orange","banana"]}
複製程式碼

第 1 個命令刪除欄位age；第 2 個命令刪除陣列fruits的第 2 個元素；第 3 個命令刪除陣列fruits的第 5 個元素，由於陣列長度只有 3，故無效果。

檔案

jj支援從檔案中讀取 JSON 串和將結果寫到檔案中。使用選項-i指定輸入檔案，選項-o指定輸出檔案。下面將從檔案fruits.txt中讀取 JSON 串，取陣列的第 2 個元素，寫到out.txt中：

$ jj -i fruits.txt -o out.txt fruits.1
複製程式碼

fruits.txt的檔案內容如下：

{"fruits":["apple","orange","banana"]}
複製程式碼

執行命令，輸出檔案的內容為：

orange
複製程式碼

格式化

jj支援將輸出的 JSON 串進行一定的格式化。選項-u移除所有的空白符，節省儲存空間。選項-p美化格式，便於閱讀。

$ echo '{"name":{"first": "li", "last":"dj"}, "age":18}' | jj -u name
{"first":"li","last":"dj"}

$ echo '{"name":{"first": "li", "last":"dj"}, "age":18}' | jj -p name
{
  "first": "li",
  "last": "dj"
}
複製程式碼

效能

與另一個 JSON 的命令列工具jq相比，jj是其效能的 10 倍以上。因為jj不會驗證 JSON 串的有效性，並且它只關心鍵路徑指定的值，一旦該值處理完成就停止。這裡有效能對比：github.com/tidwall/jj#…

用途

jj一個很方便的用途在於日誌處理，當前很多日誌庫都支援 JSON 的格式，例如前面我們介紹的logrus。我們可以使用jj在這些日誌中找到相應的資訊。我們先用logrus生成 20 條玩家登陸和下線的日誌：

package main

import "github.com/sirupsen/logrus"

func main() {
  logrus.SetFormatter(&logrus.JSONFormatter{})

  for i := 1; i <= 10; i++ {
    logrus.WithFields(logrus.Fields{
      "userid": i,
    }).Info("login")
    logrus.WithFields(logrus.Fields{
      "userid": i,
    }).Info("logoff")
  }
}
複製程式碼

生成日誌儲存在log.txt檔案中：

{"level":"info","msg":"login","time":"2020-03-26T23:36:04+08:00","userid":1}
{"level":"info","msg":"logoff","time":"2020-03-26T23:36:04+08:00","userid":1}
{"level":"info","msg":"login","time":"2020-03-26T23:36:04+08:00","userid":2}
{"level":"info","msg":"logoff","time":"2020-03-26T23:36:04+08:00","userid":2}
{"level":"info","msg":"login","time":"2020-03-26T23:36:04+08:00","userid":3}
{"level":"info","msg":"logoff","time":"2020-03-26T23:36:04+08:00","userid":3}
{"level":"info","msg":"login","time":"2020-03-26T23:36:04+08:00","userid":4}
{"level":"info","msg":"logoff","time":"2020-03-26T23:36:04+08:00","userid":4}
{"level":"info","msg":"login","time":"2020-03-26T23:36:04+08:00","userid":5}
{"level":"info","msg":"logoff","time":"2020-03-26T23:36:04+08:00","userid":5}
{"level":"info","msg":"login","time":"2020-03-26T23:36:04+08:00","userid":6}
{"level":"info","msg":"logoff","time":"2020-03-26T23:36:04+08:00","userid":6}
{"level":"info","msg":"login","time":"2020-03-26T23:36:04+08:00","userid":7}
{"level":"info","msg":"logoff","time":"2020-03-26T23:36:04+08:00","userid":7}
{"level":"info","msg":"login","time":"2020-03-26T23:36:04+08:00","userid":8}
{"level":"info","msg":"logoff","time":"2020-03-26T23:36:04+08:00","userid":8}
{"level":"info","msg":"login","time":"2020-03-26T23:36:04+08:00","userid":9}
{"level":"info","msg":"logoff","time":"2020-03-26T23:36:04+08:00","userid":9}
{"level":"info","msg":"login","time":"2020-03-26T23:36:04+08:00","userid":10}
{"level":"info","msg":"logoff","time":"2020-03-26T23:36:04+08:00","userid":10}
複製程式碼

由於每一行都是一個單獨的 JSON 串，我們可以使用jj支援的 JSON 行特性，使用..路徑標識這些行。..使得jj將這些行看成陣列的元素。我們可以讀取這些陣列元素。

獲取陣列長度，返回 20：

$ jj -i log.txt ..#
20
複製程式碼

只讀取每一行中的userid資訊：

$ jj -i log.txt ..#.userid
[1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10]
複製程式碼

只讀取每一行中的msg資訊：

$ jj -i log.txt ..#.msg
["login","logoff","login","logoff","login","logoff","login","logoff","login","logoff","login","logoff","login","logoff","login","logoff","login","logoff","login","logoff"]
複製程式碼

更復雜一點的，如果我們要檢視所有userid=1的日誌：

$ jj -i log.txt ..#\(userid=1\)# -p
[  
  {
    "level": "info",
    "msg": "login",
    "time": "2020-03-26T23:36:04+08:00",
    "userid": 1
  },
  {
    "level": "info",
    "msg": "logoff",
    "time": "2020-03-26T23:36:04+08:00",
    "userid": 1
  }
]
複製程式碼

上面的命令注意兩點，(和)是 shell 中的特殊字元，需要\轉義。命令中我們使用-p選項使結果更易讀。

如果我們只需要查詢第一條符合條件的日誌，則可以去掉最右側的#：

$ jj -i log.txt ..#\(userid=1\) -p
{
  "level": "info",
  "msg": "login",
  "time": "2020-03-26T23:36:04+08:00",
  "userid": 1
}
複製程式碼

如果要檢視所有的登入資訊：

$ jj -i log.txt ..#\(msg="login"\)# -p
[
  {
    "level": "info",
    "msg": "login",
    "time": "2020-03-26T23:36:04+08:00",
    "userid": 1
  },
  {
    "level": "info",
    "msg": "login",
    "time": "2020-03-26T23:36:04+08:00",
    "userid": 2
  },
  {
    "level": "info",
    "msg": "login",
    "time": "2020-03-26T23:36:04+08:00",
    "userid": 3
  },
  {
    "level": "info",
    "msg": "login",
    "time": "2020-03-26T23:36:04+08:00",
    "userid": 4
  },
  {
    "level": "info",
    "msg": "login",
    "time": "2020-03-26T23:36:04+08:00",
    "userid": 5
  },
  {
    "level": "info",
    "msg": "login",
    "time": "2020-03-26T23:36:04+08:00",
    "userid": 6
  },
  {
    "level": "info",
    "msg": "login",
    "time": "2020-03-26T23:36:04+08:00",
    "userid": 7
  },
  {
    "level": "info",
    "msg": "login",
    "time": "2020-03-26T23:36:04+08:00",
    "userid": 8
  },
  {
    "level": "info",
    "msg": "login",
    "time": "2020-03-26T23:36:04+08:00",
    "userid": 9
  },
  {
    "level": "info",
    "msg": "login",
    "time": "2020-03-26T23:36:04+08:00",
    "userid": 10
  }
]
複製程式碼

總結

jj是一個非常使用的 JSON 命令列工具，效能超讚。執行jj -h去看看其他選項吧。

大家如果發現好玩、好用的 Go 語言庫，歡迎到 Go 每日一庫 GitHub 上提交 issue?

參考

  1. jj GitHub：github.com/tidwall/jj
  2. Go 每日一庫 GitHub：github.com/darjun/go-d…

我

我的部落格：darjun.github.io

歡迎關注我的微信公眾號【GoUpUp】，共同學習，一起進步~

Go 每日一庫之 jj

相關文章