jq

# jq — JSON Querying and Transformation ## Overview `jq` is the standard CLI tool for querying and reshaping JSON. This skill covers practical, expert-level usage: filtering deeply nested data, transforming structures, aggregating values, and composing `jq` into shell pipelines. Every example is copy-paste ready for real workflows. ## When to Use This Skill - Use when parsing JSON output from APIs, CLI tools (AWS, GitHub, kubectl, docker), or log files - Use when transforming JSON structure (rename keys, flatten arrays, group records) - Use when the user needs `jq` inside a bash script or one-liner - Use when explaining what a complex `jq` expression does ## How It Works `jq` takes a filter expression and applies it to JSON input. Filters compose with pipes (`|`), and `jq` handles arrays, objects, strings, numbers, booleans, and `null` natively. ### Basic Selection ```bash # Extract a field echo '{"name":"alice","age":30}' | jq '.name' # "alice" # Nested access echo '{"user":{"email":"a@b.com"}}' | jq '.user.email' # Array index echo '[10, 20, 30]' | jq '.[1]' # 20 # Array slice echo '[1,2,3,4,5]' | jq '.[2:4]' # [3, 4] # All array elements echo '[{"id":1},{"id":2}]' | jq '.[]' ``` ### Filtering with `select` ```bash # Keep only matching elements echo '[{"role":"admin"},{"role":"user"},{"role":"admin"}]' \ | jq '[.[] | select(.role == "admin")]' # Numeric comparison curl -s https://api.github.com/repos/owner/repo/issues \ | jq '[.[] | select(.comments > 5)]...