promise-type-json

Promise type for manipulating json files

Attributes

Examples

Write to a whole file

To write to a json file, you can do:

bundle agent main
{
  json:
    "/tmp/newfile.json"
      array => '["hello", "world"]';
}

The resulting /tmp/newfile.json will only contain the array:

["hello", "world"]

If the /tmp/newfile.json doesn’t exist, it will be created. If it exists and contains some data, they will be overwritten.

Write to a specific field

Given a json file /tmp/oldfile.json,

{
  "foo": "bar"
}

we can modify/append a field by doing:

bundle agent main
{
  json:
    "/tmp/oldfile.json:greeting"
      array => '["hello", "world"]';
}

And the content of /tmp/oldfile.json will become:

{
  "foo": "bar",
  "greeting": ["hello", "world"]
}

If the field doesn’t exist, it is appended. If it already exists, its data will be overwritten.

Writing arrays

In order to write compound type such as arrays containg booleans, numbers, etc… One has to use the data type in the policy.

To see what happens if we use

bundle agent main
{
  vars: 
    "json_data"
      data => '[1.2, true, "hello!"]';
    
    "real_list"
      rlist => {"1.2", "2.3"};
    "bool_list"
      slist => {"true", "false"};

  json:
    "/tmp/example_1.json:json_data"
      array => "@(json_data)";
  
    "/tmp/example_2.json:real_list"
      array => "@(real_list)";
    "/tmp/example_2.json:bool_list"
      array => "@(bool_list)";
}

We can compare the content of /tmp/example_1.json and /tmp/example_2.json:

{
  "json_data": [1.2, true, "hello!"]
}

{
  "real_list": ["1.2", "2.3"],
  "bool_list": ["true", "false"]
}

As we can see, using slist, rlist or ilist to write arrays will always result in array of strings. If we want more complex arrays using containg number, true, false or null, then we need to use the data container type.

Not implemented yet

The copy attribute allows to copy the content of a json file into another json file. For example, /tmp/oldfile.json contains the following:

{
 "hello": "world"
}

We can copy it into the /tmp/newfile.json in the field "oldfile" by doing:

bundle agent main
{
  json:
    "/tmp/newfile.json:oldfile"
      copy => "/tmp/oldfile.json";
}

{
  "oldfile": {
    "hello": "world"
  }
}

Authors

This software was created by the team at Northern.tech, with many contributions from the community. Thanks everyone!

Contribute

Feel free to open pull requests to expand this documentation, add features, or fix problems. You can also pick up an existing task or file an issue in our bug tracker.

License

This software is licensed under the MIT License. See LICENSE in the root of the repository for the full license text.