How to parse JSON by command Line in Linux

13 / Dec / 2013 by arshad 1 comments

Java development is often challenging, especially when you need to parse JSON from the command line. In my recent Java development project I had parse JSON from the command line and I explored available options one-by-one to find a close fit solution which can be implemented quickly. 

Requirements

To parse json from the command line you’ll need a software called jq which is a command line JSON processor.

Installation

Step1: Download jq Binary

For 64-bit linux OS:  wget http://stedolan.github.io/jq/download/linux64/jq

For 32-bit linux OS : wget

Step 2: chmod +x ./jq

Step 3: sudo cp jq /usr/bin

In this blog, I will explain things with the help of Demo.json or demo.txt

[js]
{
"OwnerId": "xyz",
"ReservationId": "abc",
"Groups": [],
"State": {
"Code": 0,
"Name": "pending"
},
"Instances": [
{
"Monitoring": {
"State": "disabled"
},
"SecurityGroups": [
{
"GroupName": "default",
"GroupId": "sg-xxxx"
}
],
"NetworkInterfaces": [
{
"PrivateIpAddresses": [
{
"PrivateDnsName": "ip-xx-xx-yy-yyy",
"Primary": true,
"PrivateIpAddress": "xx.xx.yy.yyy"
}
],
"PrivateDnsName": "ip-xxx-xx-yy-yyy"
}
]
}
]
}
[/js]

Some of the frequently used use-cases have been discussed below with Command and their respective output:

1 : To parse a JSON object:

Command :

[js]cat Demo.json | jq ‘.OwnerId'[/js]

Output :

[js]"xyz"[/js]

2: To parse a nested JSON object:

Command :

[js]cat Demo.json | jq ‘.State.Name'[/js]

Output :

[js]"pending"[/js]

3: To extract specific fields from a JSON object:

Command :

[js]cat Demo.json | jq ‘.State | { Code , Name}'[/js]

Output :

[js]{
"Name": "pending",
"Code": 0
}[/js]

4: To parse a JSON array:

Command :

[js]cat Demo.json | jq ‘.Instances[0].Monitoring'[/js]

Output :

[js]{
"State": "disabled"
}[/js]

Command :

[js]cat Demo.json | jq ‘.Instances[0].Monitoring.State'[/js]

Output :

[js]"disabled"[/js]

Command :

[js]cat Demo.json | jq ‘.Instances[0].NetworkInterfaces[0].PrivateIpAddresses[0].PrivateDnsName'[/js]

Output :

[js]"ip-xxx-xx-yy-yyy"[/js]

In cases where you only need the value; you have to remove the “” by using pipeline in linux

Command :

[js]cat Demo.json | jq ‘.OwnerId’ | cut -d "\"" -f 2[/js]

Output :

[js]xyz[/js]

Hope you will be able to parse JSON by command line for your next project.

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