DevOps in Linux — jq command

Linux jq command introduction

Note, full mind map is available at: “DevOps in Linux Mind Map”

Let’s say one day you’ve received a task from your develoment team that they wanted to know the number of running EC2 instance, their ID and ip address, and they need it urgently. In this kind of scenario, you won’t have enough time to write a nice Python boto3 script, obviously command line awscli is the best choice.

So you type the following command:

$ aws ec2 describe-instances --region us-east-1
{
    "Reservations": [
        {
            "Instances": [
                {
                    "Monitoring": {
                        "State": "disabled"
                    },
                    "PublicDnsName": "xxxx.compute-1.amazonaws.com",
                    "StateReason": {
                        "Message": "Client.UserInitiatedShutdown: User initiated shutdown",
                        "Code": "Client.UserInitiatedShutdown"
                    },
                    "State": {
                        "Code": 80,
                        "Name": "stopped"
                    },
                    "EbsOptimized": true,
                    "LaunchTime": "2022-11-30T15:22:17.000Z",
                    "PublicIpAddress": "xx.xx.xx.xx",
                    "PrivateIpAddress": "172.31.0.4",
...

If you have hundreds of instances, the output will be huge and you will have to use some sort of grep or awk command to parse the output into a nice simple format, instead, there is a tool called jq that you can use to simple achieve this. For example:

$ aws ec2 describe-instances --region us-east-1 | jq '.Reservations[].Instances[] | {InstanceId, PublicIpAddress}'
{
  "InstanceId": "i-08e704186c88bd5d9",
  "PublicIpAddress": "xx.xx.xx.xx"
}
{
  "InstanceId": "i-0d3d5cecd122ba0fc",
  "PublicIpAddress": "xx.xx.xx.xx"
}
{
  "InstanceId": "i-01925be85d7addbbb",
  "PublicIpAddress": "xx.xx.xx.xx"
}
...

What is jq

From the above use case, you probably already figured out that jq is a command-line tool for parsing and manipulating JSON data. It is written in C and has a lightweight, minimalistic and flexible syntax. It allows you to filter, extract, and transform JSON data quickly and easily…