Why cant I parse this JSON output using shell/python?

Question

Here is the output from the response I am trying to parse:

[{"name":"UsedMemory","value":{"value":"35054384","type":"java.lang.Long"}},
{"name":"FreeMemory","value":{"value":"7085264","type":"java.lang.Long"}},{"name":"Heap","value":{"value":"42139648","type":"java.lang.Long"}},{"name":"UpTime","value":{"value":"3350544","type":"java.lang.Long"}},{"name":"ProcessCPU","value":{"value":"0.3625301325982962","type":"java.lang.Double"}},{"name":"GcCount","value":{"value":"224","type":"java.lang.Long"}},{"name":"GcTime","value":{"value":"335","type":"java.lang.Long"}}]

I am storing the response in a shell variable called $jvmStats and expect to be able to retrieve a value from it based on name like this:

$jvmStats | python -c "import sys, json; print json.load(sys.stdin)['UsedMemory']"

but the response I get is:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
TypeError: list indices must be integers, not str

Pretty new to working with JSON and unfortunately don't have the ability to use jq on this system - can some one point out the problem to me? This seems like a fairly standard approach according to all the other answers I see here - so perhaps nested value parts is the problem?

Pang · Accepted Answer · 2017-06-12 07:35:48Z

4

Try this:

jvmStats | python -c "import sys, json; print json.load(sys.stdin)[0]['name']"

This is because your JSON is first a list and then a dictionary, so you need to index the list first and then the key of the dictionary.

Also, you can only index JSON by its key, not its value.

edited Jun 12, 2017 at 7:35

Pang

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answered Jun 5, 2017 at 10:19

crazyglasses

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Seer Over a year ago

looks better - thanks! Beginning to see that the format is inconsistent with what I want to achieve via python. I essentially want a one liner to output a bunch of k=v pairs. I am not the provider of the JSON and there is no guarantee there lines will come out in the same order each time - thus doing things by indices is going to be tough. I am probably better with a sed command!

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