什么是jq？jq是Linux下面把文本字符串格式化成json格式的工具
系统环境：centos 7
一、安装
（1）yum安装
a、安装epel源
# wget http://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
# rpm -ivh epel-release-latest-7.noarch.rpm
# yum repolist ###检查是否已经添加到源列表
b、yum install -y jq
（2）源码安装
a、下载源码包
# wget https://github.com/stedolan/jq/releases/download/jq-1.5/jq-1.5.tar.gz
# tar zxvf jq-1.5.tar.gz
# cd jq-1.5
# ./configure
# make && make install
编译安装完成以后就能在该目录下看见jq二进制文件了，添加到环境变量~/.bashrc
如图：
# source ~/.bashrc
安装完成，现在就可以使用jq命令
二、jq测试
（1）简单测试
# echo '{"yjt":"boy","age":20}' |jq . #注意，命令最后有一个点，代表显示全部的json文件
效果：
注意：jq命令会检查json格式的合法性，如果不合法，将保错，具体的json格式，请浏览：http://www.w3school.com.cn/json/json_syntax.asp 或者 https://stedolan.github.io/jq/manual/
（2）通过key获取值，如何获取呢？
jq '.key'
file文件内容
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{"System_Time":"2018-11-27 17:42:02","Hostname":"test.com","Network":[{"Network_Card": "bond1","ip":"10.126.140.16","Input_Traffic": "4.448K/S","Output_Traffic": "2.649K/S "},{"Network_Card": "eth4","ip":null,"Input_Traffic": "2.679K/S","Output_Traffic": "1.805K/S "},{"Network_Card": "eth6","ip":null,"Input_Traffic": "0.750K/S","Output_Traffic": "0.000K/S "}],"CPU":{"us":"0%","sy":"0%","id":"100%","wa":"0%","cpu_rate":"0.01%","CPU_Load_Average": " 0.15, 0.04, 0.01","Running_Process":"1","Total_Process":"696","Host_Running_Time":" 18 days 22:53","User_Connection_Number":"2" ,"CPU_Status":"Normal"},"Memory":{"total_mem":"128644M","use_mem": "1373M","free_mem": "127270M","use_rate": "1%","free_swap": "65535M","total_swap": "65535M","use_swap": "0M","swap_use_rate": "0%","Memory_Status":"Normal","Swap_Memory_Status":"Normal"},"disk":{"root_use":"1%","root_status":"Normal","var_use":"1%","vae_status":"Normal","data_use":"1%","data_status":"Normal","data1_use":"0%","data1_status":"Normal","data2_use":"1%","data2_status":"Normal","data3_use":"1%","data3_status":"Normal"},"TCP":{"TIME_WAIT":"36","FIN_WAIT1":"0","FIN_WAIT2":"0","CLOSE_WAIT":"0","ESTABLISHED":"2","SYN_RECV":"0","LAST_ACKV":"0","CLOSING":"0"},"type":"END"} |
例：
（3）获取不存在的key会返回null
（4）嵌套解析
（5）内建函数
a、has 用来判断是否存在某个key
b、key 用来获取json中的key元素的
例：
