Jq - Command-Line JSON Processor - cmd Cheatsheets

Understanding Jq for JSON Processing

Jq is a lightweight and flexible command-line JSON processor. It allows you to easily slice, filter, map, and transform structured data with the same power and expressiveness as sed, awk, or grep, but for JSON. This tool is invaluable for developers working with APIs, configuration files, or any data formatted in JSON.

Common Jq Commands and Usage

Below are some essential Jq commands to get you started with processing your JSON data effectively.

# To pretty print the json:
jq "." < filename.json

# To access the value at key "foo":
jq '.foo'

# To access first list item:
jq '.[0]'

# to slice and dice arrays:
jq '.[2:4]'  # Select elements from index 2 up to (but not including) 4
jq '.[ :3]'  # Select elements from the beginning up to (but not including) index 3
jq '.[-2:]' # Select the last two elements

# to extract all keys from a JSON object:
jq keys

# to sort an array of objects by a specific key (e.g., "bar"):
jq '.foo | sort_by(.bar)'

# to count the number of elements in an array or object:
jq '.foo | length'

# print only selected fields from each object in an array:
jq '.foo[] | {field_1, field_2}'

# print selected fields as plain text, joined by a space, instead of JSON:
jq '.foo[] | {field_1, field_2} | join(" ")'

# only print records (objects) where a given field matches a specific value:
jq '.foo[] | select(.field_1 == "value_1")'

Advanced Jq Filtering and Transformation

Jq's power lies in its ability to combine these basic operations to perform complex data manipulations. You can chain filters, use conditional logic, and even create new JSON structures on the fly. For instance, combining select with field extraction allows for highly targeted data retrieval.

Integrating Jq into Your Workflow

Jq is an essential tool for any developer's command-line toolkit. It integrates seamlessly with shell scripting, making it easy to automate JSON data processing tasks. Whether you're parsing API responses, validating configuration files, or preparing data for other tools, Jq provides a robust and efficient solution.

Further Resources for Jq

For more in-depth information and advanced usage, consult the official Jq documentation and community resources: