How to parse JSON tidal information from worldtides.info?

Question

My goal is to parse the result of www.worldtides.info. I have a Raspberry Pi 2 and I'm scripting with Linux.

I have an API key and the curl request is something like:

curl -s "http://www.worldtides.info/api?extremes&lat=my_latitude&lon=my_longitude&key=my_api_key"

Which gets a result like this:

{
  "status": 200,
  "requestLat": "my_latitude",
  "requestLon": "my_longitude",
  "extremes": [
    {
      "dt": 1459680132,
      "date": "2016-04-03T10:42+0000",
      "height": 0.7343567325036922,
      "type": "High"
    },
    {
      "dt": 1459702028,
      "date": "2016-04-03T16:47+0000",
      "height": -0.8438121322770741,
      "type": "Low"
    },
    {
      "dt": 1459724478,
      "date": "2016-04-03T23:01+0000",
      "height": 1.0419712550773803,
      "type": "High"
    },
    {
      "dt": 1459747135,
      "date": "2016-04-04T05:18+0000",
      "height": -1.1049607153344834,
      "type": "Low"
    },
    {
      "dt": 1459769354,
      "date": "2016-04-04T11:29+0000",
      "height": 1.1012796430343657,
      "type": "High"
    },
    {
      "dt": 1459791366,
      "date": "2016-04-04T17:36+0000",
      "height": -1.204313872235808,
      "type": "Low"
    },
    {
      "dt": 1459813613,
      "date": "2016-04-04T23:46+0000",
      "height": 1.3452661348073778,
      "type": "High"
    },
    {
      "dt": 1459835931,
      "date": "2016-04-05T05:58+0000",
      "height": -1.4062688322894952,
      "type": "Low"
    }
  ]
}

Using jq, I want to get the times of high and low tides for the current day and tomorrow, but when I try this:

.result[].type

But it gives me an error:

jq: error (at <stdin>:0): Cannot iterate over null (null)`

I know I can get the type of tide it is using this:

.extremes[].type

the result is:

High
Low
etc...

and the time of the tide using this:

.extremes[].date

the result is:

2016-04-03T10:42+0000
2016-04-03T16:47+0000
etc...

So, how do I combine the results together to get an output like this?

2016-04-03T10:42+0000 High
2016-04-03T16:47+0000 Low
etc...

Please add your desired output for that sample input to your question. — Cyrus, Apr 03 '16 at 14:12
There is no `result` key, so I'm not sure what you're trying to do. — Todd A. Jacobs, Apr 03 '16 at 14:13
Please submit a separate question for the edited second half of your post. — , Apr 03 '16 at 17:02

Tersosauros · Accepted Answer · 2016-04-04T03:13:13.680

1

Something along the lines of

curl -s "http://www.worldtides.info/api?extremes&lat=my_latitude&lon=my_longitude&key=my‌_api_key"| jq -r ".extremes[] | .date + .type"

Should give you both the date/time and High/Low tide output for each entry.

Basically, you need to use extremes NOT result. There is no result key, hence jq is giving you messages about null.

edited Apr 04 '16 at 03:13

answered Apr 03 '16 at 16:04

Tersosauros

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How to parse JSON tidal information from worldtides.info?

1 Answers1