Master JSON Formatting and Extraction on Linux with jq

What is jq?

jq is a lightweight command‑line utility for parsing, filtering and transforming JSON data. It reads JSON from stdin, files or pipelines and writes the result to stdout, making it easy to embed in shell scripts.

Installation on Linux

Most distributions provide jq in their package repositories. Install it with the appropriate package manager:

Arch Linux: sudo pacman -S jq Debian/Ubuntu/Mint: sudo apt-get install jq Fedora: sudo dnf install jq OpenSUSE: sudo zypper install jq For other distributions consult the official installation guide.

Formatting JSON for readability

Save the raw JSON to a file (e.g., liangxu.json) and run: cat liangxu.json | jq '.' The “.” filter outputs the input unchanged but pretty‑prints it with indentation.

Extracting specific fields

To retrieve the address object: jq .address liangxu.json To get the nested postalCode value: cat liangxu.json | jq .address.postalCode Filters are case‑sensitive; field names must match exactly.

Working with arrays

The phoneNumber field is an array. To list all elements: jq .phoneNumber[] liangxu.json To fetch the first element only:

jq .phoneNumber[0] liangxu.json

Built‑in functions

Two useful jq functions are demonstrated:

keys – lists all top‑level keys: cat liangxu.json | jq 'keys' has – tests for the presence of a key, returning true or false:

cat liangxu.json | jq 'has("alvin")'

Conclusion

jq covers basic formatting and extraction, and also supports arithmetic, conditionals, variable declarations and custom functions. Readers are encouraged to explore the official jq manual for advanced usage.