Transform JSON

Such functionality might be useful if you need to remove information for HIPAA compliance, or if fields need to be added or revised to meet the BIDS specification.

Delete Properties

The built-in function del removes a key and its corresponding value. Both the dot operator and parentheses are used:
jq 'del(.Modality)' test.json
Delete multiple properties by putting them in a comma-separated list inside parentheses:
jq 'del (.MagneticFieldStrength, .Modality, .PostLabelingDelay )' test.json
Pass a bash variable to jq by wrapping it in a single quotes surrounded by double quotes "'"$myvar"'":
jq 'del(."'"$myvar"'")' test.json

Revise the value of an existing property by assigning the new value with =:
jq '.Modality="MR_New"' test.json
Or, add a new key and value:
jq '.Fred="new_value"' test.json
To modify multiple properties at once, use the pipe | (if you use a comma, only the first property gets changed):
jq '.MagneticFieldStrength = 6 | .Modality="HyperMR" ' test.json

By default, jq returns results to standard output (i.e., the terminal). Use Unix redirection, > to send that output to a file:
jq 'del(.Modality)' test.json > nomodality.json
Often, what you want is to modify the input file. Unfortunately, you cannot transform the input by redirecting the output into it! Instead, you must redirect the output to a new file, and then in a second step, rename the new file to the input filename: