Finding highest value in a specific JSON field in bash - json

Question

I am writing a bash script that curls POST an API. The response from the post has values returned in the following format:
{
"other": "irrelevant-fields",
"results": [
{
"datapoints": [
{"timestamp": 1555977600, "value": 0},
{"timestamp": 1555984800, "value": 15},
{"timestamp": 1555992000, "value": 5}
]
}
]
}
I want to extract the highest figure from the "value" columns but I am having problems writing this code in bash. I am a beginner at JSON and there are no real references I can use to filter out the strings and values I don't need as each array is the same except for the timestamp, but I don't care about the timestamp, just the highest value returned.
My current code is just a generic way to extract the largest number from a file in bash:
grep -Eo '[[:digit:]]+' | sort -n | tail -n 1
...but instead of 15, that returns 1555992000.

Answer 1

echo '
{
"other": "irrelevant-fields",
"results": [
{
"datapoints": [
{"timestamp": 1555977600, "value": 0},
{"timestamp": 1555984800, "value": 15},
{"timestamp": 1555992000, "value": 5}
]
}
]
}
' | jq '.results[].datapoints | max_by(.value)'
The output will be like this:
{
"timestamp": 1555984800,
"value": 15
}
For more information, see this Medium post on jq, or the program's home page at https://stedolan.github.io/jq/

Answer 2

Please process JSON with a proper JSON interpreter/parser, like Xidel.
$ cat <<EOF | xidel -s - -e '$json/max((.//datapoints)()/value)'
{
"other": "irrelevant-fields",
"results": [
{
"datapoints": [
{"timestamp": 1555977600, "value": 0},
{"timestamp": 1555984800, "value": 15},
{"timestamp": 1555992000, "value": 5}
]
}
]
}
EOF
This returns 15.
(or in full: -e '$json/max((results)()/(datapoints)()/value)')