Question 207525 in Json Question posted in
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Get the first JSON object from a file containing a sequence of JSON objects

I have a file containing a sequence of json objects. Using the jq tool, how can I get the first json object from that file?

I have tried jq limit(1; .) input.jsonl but that limits the length of each individual object in the file, rather than giving me just the first object. I have also read through the whole of the jq man page! Maybe I missed something.

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3

Answers


  1. Chosen as BEST ANSWER
    0

    Well okay one way to do it is like this:

    jq -c . INPUT.JSONL  | head -n 1 | jq

    The -c option says to output the entries one per line, then head gets the first line, then we pretty-print it again with jq. Surely there is a way to do this with just a single invokation of jq?


  2. 0

    For an input file like

    {
  "a": "b"
}
{
  "c": "d"
}

    you could

    • slurp the entire input and then print the first array element:

      $ jq -s '.[0]' in.json 
{
  "a": "b"
}

    • use null-input, and then inputs:

      $ jq -n '[inputs][0]' in.json 
{
  "a": "b"
}
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  3. 0

    Null input (-n) is useful in such a case:

    jq -n 'input' file.json

    The input filter will read a single JSON element from the provided input stream.

    Example:

    jq -n 'input' <<JSON
{ "first element": [ 1, 2 ] }
{ "second element": [ 3, 4, 5 ] }
JSON

    Output:

    {
  "first element": [
    1,
    2
  ]
}
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