Append new element to JSON object in specific format using bash and jq

Question

I would like to append an element to an existing JSON file where I have the working directory as the key and the working directory + the contents as the value in a string array format.

Lets say I have the following structure:

 Docs (Directory)
 |
 +-- RandomFile.json
 |    
 +-- Readme (Working Directory)
 |  |  
 |  +-- Readme.md
 |  +-- Readyou.md

What I would like to achieve is the structure below with the working directory as the prefix for every element in the array.

"Readme": ["Readme/Readme.md", "Readme/Readyou.md"]

From the output above, I would like to append that to the contents of the RandomFile.json which currently looks like this:

{
  "docs": {
    "Doc": ["doc1"]
  }
}

to this:

{
  "docs": {
    "Doc": ["doc1"],
    "Readme": ["Readme/Readme.md", "Readme/Readyou.md"]
  }
}

Is it something that can be managed straightforward using bash and jq?

If Readme is the working directory, do you know that ../RandomFile.json is the name of the file to modify, or just that there is a single JSON file in the parent directory that should be modified? — chepner
– chepner, Commented Jan 13, 2020 at 16:01

chepner · Accepted Answer · 2020-01-13 16:11:22Z

1

This requires jq 1.6 in order to use the --args option.

$ jq --arg wd "$(basename "$PWD")" '.docs+={($wd): $ARGS.positional | map("\($wd)/\(.)")}' ../RandomFile.json --args *
{
  "docs": {
    "Doc": [
      "doc1"
    ],
    "Readme": [
      "Readme/Readme.md",
      "Readme/Readyou.md"
    ]
  }
}

The shell is used to pass the base name of the current working directory as the variable $wd.
The shell is also used to pass the names of all the files in the current working directory as separate arguments.
The file to edit is assumed to be ../RandomFile.json; if you only know that there is a JSON file in the parent, you can use ../*.json instead.
Use += to update the .docs object of the original with a new key (the working directory) and list of file names. map prefixes each element of $ARGS.positional with $wd.

answered Jan 13, 2020 at 16:11

chepner

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