jq

1. Invoking jq

   Command-line options such as -r, -c, -s, --arg.

2. Basic filters

   Identity, object and array indexing, slices, pipes, recursive descent.

3. Types and values

   JSON types, null, numbers, strings and constructors.

4. Builtin operators and functions

   Arithmetic, length, keys, map, select, sort, group_by.

5. Conditionals and comparisons

   if-then-else, boolean logic and alternative operator.

6. Regular expressions

   test, match, capture, sub and gsub.

7. Reduce and foreach

   Reduce, foreach, limit and recursion.

8. Assignment

   Update operators |=, = and arithmetic update.

9. Variables and functions

   Variable binding, destructuring and user-defined functions.

10. Streaming

    Streaming large inputs with --stream and tostream.

11. I/O

    Reading input, debugging and stderr.

12. Modules

    Importing modules with import and include, search paths and organizing reusable jq code.

Each section links to the official page. Titles and summaries by Extra Credit; the docs belong to their authors.