Table of Contents
- Prettify
- Array Filters
- Object Filters
- Array of Objects
- Nested Array
- Advanced Filters
- The select() Function
- The map() Function
- Slicing Arrays and Strings
- Regular Expressions
- Summary
1. Prettify
The simplest jq filter is ‘.’ which prints the input as it is, but adding the ‘-C’ flag can prettify the output with colors.
jq -C '.' sample.json
Sample JSON input:
{"name": "jq tutorial", "version": "1.0"}
Output:
{
"name": "jq tutorial",
"version": "1.0"
}
2. Array Filters
To filter an array and return its elements, you can use the ‘[.[]]’ syntax.
jq '.[]' sample.json
Sample JSON input:
["jq tutorial", 1.0]
Output:
"jq tutorial" 1.0
3. Object Filters
To filter and retrieve a specific property from an object, use ‘.property_name’.
jq '.name' sample.json
Sample JSON input:
{"name": "jq tutorial", "type": "filter"}
Output:
"jq tutorial"
4. Array of Objects
To get a list of values from an array of objects, you can use ‘.[] | .property_name’.
jq '.[] | .name' sample.json
Sample JSON input:
[{"name": "jq tutorial"}, {"name": "filter guide"}]
Output:
"jq tutorial" "filter guide"
5. Nested Array
To navigate through a nested array, combine array filters and object filters.
jq '.[][]' sample.json
Sample JSON input:
[[1,2],[3,4]]
Output:
1 2 3 4
6. Advanced Filters
For more complex data manipulation, combine and chain jq filters as needed.
jq '.users[] | select(.age > 21).name' sample.json
Sample JSON input:
{"users": [{"name": "Alice", "age": 22}, {"name": "Bob", "age": 20}]}
Output:
"Alice"
7. The select() Function
The select() function is crucial for filtering arrays and objects based on conditions.
jq '.users[] | select(.active)' sample.json
Sample JSON input:
{"users": [{"name": "Alice", "active": true}, {"name": "Bob", "active": false}]}
Output:
{"name": "Alice", "active": true}
8. The map() Function
Use the map() function to apply a filter to each element of an array.
jq 'map(. + 1)' sample.json
Sample JSON input:
[1, 2, 3]
Output:
[2, 3, 4]
9. Slicing Arrays and Strings
To slice arrays or strings, use the syntax ‘start:end’.
jq '.[1:3]' sample.json
Sample JSON input:
["a", "b", "c", "d"]
Output:
["b", "c"]
10. Regular Expressions
For pattern matching using regular expressions, use the ‘test()’ function.
jq 'select(.name | test("^(jq)"))' sample.json
Sample JSON input:
[{"name": "jq tutorial"}, {"name": "regex guide"}]
Output:
{"name": "jq tutorial"}
Summary
In this tutorial, we covered various jq filters to jq filter json data, including prettification, filtering arrays and objects, using select() and map() for conditional selection and transformation, and slicing and regex for precise data extraction. With these techniques, you’re well-equipped to manipulate and query any JSON data effectively.
References
- jq Manual – https://stedolan.github.io/jq/manual/
- jq Tutorial – https://stedolan.github.io/jq/tutorial/
