Found the answer:

cat <file>.json | jq -r '.files[] | select(.fileName=="FOO") | .md5'

Very close! In your select expression, you have to use a pipe (|) before contains.

This filter produces the expected output.

. - map(select(.Names[] | contains ("data"))) | .[] .Id

The jq Cookbook has an example of the syntax.

Filter objects based on the contents of a key

E.g., I only want objects whose genre key contains "house".

$ json='[{"genre":"deep house"}, {"genre": "progressive house"}, {"genre": "dubstep"}]'
$ echo "$json" | jq -c '.[] | select(.genre | contains("house"))'
{"genre":"deep house"}
{"genre":"progressive house"}

Colin D asks how to preserve the JSON structure of the array, so that the final output is a single JSON array rather than a stream of JSON objects.

The simplest way is to wrap the whole expression in an array constructor:

$ echo "$json" | jq -c '[ .[] | select( .genre | contains("house")) ]'
[{"genre":"deep house"},{"genre":"progressive house"}]

You can also use the map function:

$ echo "$json" | jq -c 'map(select(.genre | contains("house")))'
[{"genre":"deep house"},{"genre":"progressive house"}]

map unpacks the input array, applies the filter to every element, and creates a new array. In other words, map(f) is equivalent to [.[]|f].

You want to run a .context,.score filter on each element of v I think:

$ jq -r '.[] | [.c, .e, .score, (.v[] | .context,.score)] | @csv' file.json
"A","B",0.99,"asdf",0.98,"bcdfd",0.97

This is equivalent to using the builtin map function without assembling the results back into an array.

You can use jq '.[] | .login, .id' to obtain each login followed by its id.

The -r option should not be used if the output will be fed into another JSON parser; only the last jq in the pipeline should use it – otherwise you risk feeding non-JSON data into the second jq instance.

Your last example with .[0].t seems correct and works with jq 1.6.

$ cat json | jq '.tx' | jq -r '.[0].t'
t for a

But this can be simplified to a single jq invocation, first incrementally to:

$ cat json | jq -r '.tx | .[0].t'
t for a

and then finally to:

$ cat json | jq -r '.tx[0].t'
t for a

$ jq -r '.[].username' my_file.json
jdoe
jadoe

jq '.fields |= ( map(.key = .name | del(.type,.linkedId,.name)) | from_entries )' file

This updates the fields array. First, for each element (using map()), a key key is created with the value from the name key. Then the type, linkedId, and name keys are deleted from the element. We are now left with a key and a value key in each element of the fields array, which is just what from_entries needs to associate the key values as keys to the value values.

Testing on the data given in the question (with a trailing comma removed), this generates the following JSON:

{
  "name": "Papanito",
  "fields": {
    "Name1": "Value1",
    "Name2": "Value2",
    "Name3": "Value3",
    "Name4": "Value3"
  }
}

Note that your expected output is invalid JSON, as an array can't have keys. Therefore, the fields value in the output above is an object, not an array.

Would you want to keep fields as an array, you could rearrange the operations a bit:

jq '.fields |= map([.key = .name | del(.type,.linkedId,.name)] | from_entries)' file

For the given data (corrected as mentioned above), this would generate something equivalent to the following document:

{
   "name": "Papanito",
   "fields": [
      { "Name1": "Value1" },
      { "Name2": "Value2" },
      { "Name3": "Value3" },
      { "Name4": "Value3" }
   ]
}

This has the benefit that two elements with the same original name values would not overwrite each other in the result.

Conceptually, the above deletes the data that we no longer want. The following variations extract the data we want instead.

This generates the last result from above:

jq '.fields |= map({ (.name): .value })' file

And we can get the first result (with fields as a single object) by merging the entries in the list:

jq '.fields |= (map({ (.name): .value }) | add)' file

Found out the answer

jq 'select(.items | index("blue"))'

Adapted from this post on Processing JSON with jq, you can use the select(bool) like this:

$ jq '.[] | select(.location=="Stockholm")' json
{
  "location": "Stockholm",
  "name": "Walt"
}
{
  "location": "Stockholm",
  "name": "Donald"
}