Lightweight standalone CLI utility to read and manipulate JSON documents in a semantically safe way.

Some ideas/TODO-s for the future:

• tests
• flexible error reporting
• merge action for merging two objects or arrays according to rfc7396
• rfc6901 (JSON Pointers) support
• configurable formatting and/or keeping whitespaces

Compiling

gcc main.c -ojson-util

Usage

json-util ACTION [ARGUMENTS...]

If action requires JSON input, it could be given via stdin. If multiple input values are needed (e.g. values, set and splice actions), they could be concatenated with recommended whitespace between them (for numbers and literal values). In that case, if any value comes from untrusted source, it is recommended to pass the value through check action so it does not interfere with other values (unterminated objects, string, arrays, ...). Everything after required number of input values is ignored.

If action outputs JSON, it will be printed to stdout as raw JSON value. Objects and arrays will be formatted with tab as indentation character. Duplicate keys are not removed.

In case of invalid input (bad JSON, unexpected value type, bad argument, integer overflow), exit code will be 1. Otherwise it will be 0 even if action fails for any other reason (e.g. non-existent value).

Example:

$ printf '{"a":{"b":["c"]}} ignored text' | json-util get a.b.0
"c"

Currently supported actions:

• check

Check that input contains 1 and exacltly 1 valid JSON value and nothing more. Prints "ERROR" to standard output if that is not the case, otherwise prints nothing. Exit code will be 0 in both cases.

• value [index]

Outputs single input value at index index or 0 if index is not given. Outputs nothing if requested value cannot be read from input.

• type

Print type name (object, array, string, number, boolean or null) of input JSON value.

• get pathname

Get a JSON value at given path. Path is period-delimited sequence of path components. If path component contains period (.) or backslash (\), they must be escaped with backslash (\). If any object at path contains duplicate key, the last key/value will be used. Output will be empty if path cannot be resolved.

• keys

Expects single JSON object as input and outputs list of keys in object, one per line, encoded as JSON string. Keys are listed in same order they appear in input object. No deduplication is done.

• set pathname

Set JSON value at given path. Accepts 2 JSON input values - first is the document to be modified and second (optional) is assigned value. If path cannot be resolved, document will be unmodified. If any object at path contains duplicate key, the last key/value will be used. Previous key/value pairs won't be affected.

If value pointed by path is an array and index is out of range, the gap will be filled with null values.

Property can be deleted by not giving the second value. In this case, if the value pointed by path is an array, the behaviour will be the same as assigning null value - similar to JavaScript.

• splice [index] [count]

Similar to Javascript Array#splice method. Accepts array as first input value and inserts other values at given index, while removing up to count old element at given index. If index is not given or is out of range, it will be set to the length of the array. If count is not given, it will be set to 0.

• decode-string

Decode JSON encoded string into UTF-8 encoded byte sequence.

• encode-string

Encode data from stdin to be safe for use in JSON string.

• encode-key path-component

Escape periods (.) and backslashes (\) with backslash (\).

License

MIT