abclib / bj.sh

Simple Bash JSON parser

bj.sh is a pure GNU Bash library for parsing JSON data.

bj.sh is meant to be run as a script, sourced as a library, or copied directly in to your script for maximum flexibility. Great for embedded systems, build automation, or any environment where 'jq' isn't available (Plus, bj.sh is 1/20th the size of the 'jq' binary)

bj.sh is NOT a JSON validator, behavior is undefined if given invalid JSON! It will detect some basic JSON errors, but this is not the goal of bj.sh.

The entire parser is implemented as a single bash function, so it can be sourced in to your own script, or you can just copy and paste the function in to your script to reduce your external dependencies. bj-80x13.sh (80-character lines, 13 lines long) and bj-90x12.sh (90-character lines, 12 lines long) versions are intended for exactly this.

Usage

Called as an external script:

bj.sh [DATA] [QUERY ...]

Sourced or copied in to your script:

source bj.sh
bj [DATA] [QUERY ...]

DATA can be a JSON string, or -. If DATA is -, JSON data is read from stdin.

QUERY terms are the keys and indexes you want to query from the JSON data.

Examples

source bj.sh
r=$(bj '{"foo": {"bar": "baz"}}' foo bar)

r will be set to the string baz.

r=$(curl https://myapi.example.com/api/call | bj - nodes 0)

Assuming the api call returns something like {"nodes": ["node0", "node1"]}, this will set r to node0. To get the list of nodes and iterate over them:

nodes=$(curl https://myapi.example.com/api/call | bj - nodes)
i=0
while node=$(bj "$nodes" "$i"); do
    ping -c1 "$node"
    (( i++ ))
done

bj will return the JSON data at the key if it's not a leaf node, so the first call returns ["node0", "node1"]. Also, bj will exit with a code of 1 if the queried key or index doesn't exist. So, when $i is 2, bj will return 1, breaking out of the while loop.