json-parser

A small command-line JSON explorer with a path-based query language (jq-lite). Load a JSON file, inspect its shape, and pull out values interactively or from scripts.

Quick start

cmake -S . -B build
cmake --build build
./build/json_parser mine.json

At the json> prompt:

json> structure 2
json> players[0].player
json> players[*].player
json> help
json> exit

Usage

Interactive REPL

./json_parser path/to/file.json

• Type a query to print matching values as JSON.
• Type a meta-command (help, print, structure, …) for REPL actions.
• Press Tab for autocomplete (fields, array indices, string keys).
• Use Up/Down for history.
• Invalid queries print an error and the REPL keeps running.

One-shot mode (-q)

Run a single query and exit — useful for scripts and pipes:

./json_parser mine.json -q 'players[0].player'
./json_parser mine.json -q 'players[*].inventory[*].item'

Exit code is non-zero if the query fails.

REPL meta-commands

Command	Description
help	Show query syntax and commands
print or .	Dump the full loaded JSON
structure or tree	Folder-tree view of the file (keys, types, counts)
structure 3 or tree 3	Same, but limit depth (handy for large files)
clear	Clear the screen
exit	Quit

The structure view uses colors: blue {n} for objects, green [n] for arrays, and dimmed previews for leaf values.

Query language

Queries are a chain of steps applied left to right:

Step	Example	Meaning
Field	players	Object member by name
Dot + field	.player	Same (dot is optional between steps)
Array index	[0]	Element at index
Array wildcard	[*]	Every element
String key	["meta"]	Object member by string key

Examples (using mine.json):

players                          # the players array
players[0]                       # first player object
players[0].player                # "Steve"
players[0].location              # location object
players[0].inventory[0].item     # "Diamond Sword"
players[*].player                # all player names
players[0]["settings"].gamemode  # string-key access

Each matching value is printed as valid JSON on its own line.

Autocomplete

While typing a query, press Tab to see suggestions based on the loaded file:

• Object fields after . or at the start of a step
• Array indices after [
• String keys inside ["…"]

Suggestions show type hints (e.g. players[3], inventory{8}) and colors for objects vs arrays.

Building and testing

cmake -S . -B build
cmake --build build
ctest --test-dir build

Requires C++20, CMake, and replxx (for the REPL). See CMakeLists.txt for how replxx is located.

Docker

A multi-stage Dockerfile is included for containerized builds.

Project layout

Path	Role
json/	JSON scanner, parser, AST, serializer
Query/	Query scanner, parser, evaluator
cmd/	Autocomplete, structure tree
tests/	GoogleTest suite
mine.json	Sample file for trying queries