[SOLVED] how to properly pass arguments to jq

Issue

I'm trying to add a json file's name as a key to the file structure itself. For example:

Input:

test.json 
{}

Output:

test.json
{
    "test": {}
}

These are the commands I'm trying:

output=`cat $file` | jq --arg fn "$file_name" '. += {"$fn" : {}}' 

or

# file_name already contains file name without extension
output=`cat $file | jq --argjson k '{"$file_name": {}}' '. += $k'`

echo "$output" > $file

However, the outputs are:

test.json
{
     "$fn": {}
}

test.json
{
     "$file_name": {}
}

How do I make sure jq can recognize args as a variable and not a string literal ?

Solution

Using input_filename (and rtrimstr to remove the extension):

jq '.[input_filename | rtrimstr(".json")] = {}' test.json

Using --arg and a variable initialized from outside:

jq --arg fn "test" '.[$fn] = {}' test.json 

Output:

{
  "test": {}
}

Answered By - pmf

Answer Checked By - Katrina (WPSolving Volunteer)