Unable to get the last object from json using jq-CodePudding

I'm not able to get the last object filtered after using jq select. To demonstrate this issue, I got the following simple json file that contains list of IP addresses:

file.json

{
  "ip": "1.1.1.1",
  "tested_count": 17,
  "last_scan_date": "1673146101"
}
{
  "ip": "1.1.1.1",
  "tested_count": 17,
  "last_scan_date": "1673146107"
}
{
  "ip": "2.2.2.2",
  "tested_count": 17,
  "last_scan_date": "1673146109"
}
{
  "ip": "1.1.1.1",
  "tested_count": 10,
  "last_scan_date": "1673152750"
}
{
  "ip": "1.2.3.4",
  "tested_count": 11,
  "last_scan_date": "1673152755"
}

In order to list out the data for IP 1.1.1.1, I will do the following in bash script:

#!/bin/bash
TARGET="1.1.1.1"
jq -r 'select(.ip=="'"${TARGET}"'")' file.json

The above will output:

{
  "ip": "1.1.1.1",
  "tested_count": 17,
  "last_scan_date": "1673146101"
}
{
  "ip": "1.1.1.1",
  "tested_count": 17,
  "last_scan_date": "1673146107"
}
{
  "ip": "1.1.1.1",
  "tested_count": 10,
  "last_scan_date": "1673152750"
}

Now, what I want is the last output for this IP 1.1.1.1 with the last_scan_date 1673152750 .

So I tried one of these:

jq -r 'select(.ip=="'"${TARGET}"'") | last' file.json (does not work)

I got error:

> jq: error (at file.json:5): Cannot index object with number
> jq: error (at file.json:10): Cannot index object with number
> jq: error (at file.json:20): Cannot index object with number

jq -r 'last(select(.ip=="'"${TARGET}"'"))' file.json (does not work)
jq -r 'select(.ip=="'"${TARGET}"'") | .[-1]' file.json (does not work)
jq -r 'select(.ip=="'"${TARGET}"'") | to_entries | last' file.json (does not work)

The expected output is:

{
  "ip": "1.1.1.1",
  "tested_count": 10,
  "last_scan_date": "1673152750"
}

I searched about this but mostly they are talking about getting the last array but I don't have array here just objects. Can jq actually do this?

CodePudding user response：

You don't need to add arrays brackets beforehand. Either make the input stream an array by using the -s command-line option, and access the items with .[], or use inputs to fetch the items (which requires the -n option). Then, last can give you the preferred item.

Using -s and .[]:

jq -sr --arg ip '1.1.1.1' 'last(.[] | select(.ip==$ip)).last_scan_date'

Demo

Using -n and inputs:

jq -nr --arg ip '1.1.1.1' 'last(inputs | select(.ip==$ip)).last_scan_date'

Demo

Output:

1673152750

Note: Use --arg to introduce external values.