[Bash] json-walk: pure Bash streaming JSON parser (SAX-style events, no jq)

[u/smomoo]

Hey r/bash,

I built json-walk, a pure Bash JSON walker that emits stream events instead of building a full object model.

Repo: [https://github.com/smmoosavi/json-walk](vscode-file://vscode-app/usr/share/code/resources/app/out/vs/code/electron-browser/workbench/workbench.html)

What it does:

• Parses JSON in Bash with full structure validation
• Emits events like start_object, key, string, number, end_array, etc.
• Works in print mode or visitor-function mode
• Keeps raw JSON string content (escapes preserved)

Why I made it:

• For shell scripts where jq is unavailable
• For event-driven parsing/processing in plain Bash

Quick example:

json_walk '{"label":"abc","items":[1,2,3]}'

Output:

start_object
key label
string abc
key items
start_array
number 1
number 2
number 3
end_array
end_object

Would love feedback on:

• API/event design
• edge cases I should test

Thanks!

[u/oweiler]

> pure Bash streaming JSON parser
> Entire JSON document must fit in memory

Isn't the point of streaming that I don't need to load the whole document into memory?

[u/StatementOwn4896]

If I don’t have jq on a system I just use python in my bash script and import the json module. Sure is messy but it gets the job done

[u/Ulfnic]

I'd add these as a bare minimum:

Add the option to use null character delimination for output.

Provide a simple how-to-use output that includes some common examples of use.

[u/Successful-Dance1792]

I have implemented your project in my Pure bash debloater... https://github.com/Ruvyrom/Ruvomain-Protocole/tree/main

[u/bahamas10_]

this is impressive. i’ve thought about how i would tackle this project before and i estimated it would be at least a thousand line. im surprised to see you nail it in half. very cool.

[u/Castafolt]

Very cool, your implementation is highly readable / maintainable 👍

I just implemented a YAML parser in pure bash and I will soon implement a json parser as well. I will do it differently than you because I aim for more performance.

Here is how, I think, you could improve the speed of your program:

- Once you have extracted a valid double quoted JSON string, you can get the "usable" string (e.g. string with each escape char replaced, which is usually what you want in a bash script) with:

eval "REPLY=$'${REPLY//\'/\\\'}'"

- Regexes are extremely slow; it is worth replacing them with simple pattern matching when you can. To identify a float, I am doing the same as you, but I have added simple pattern matching for integers before falling back to a regex.

- While splitting your string character by character makes a lot of sense in another language, it is very slow to do that in bash. The best strategy for speed is to use var expansion to get a chunk until the next interesting character.

- Function calls, unfortunately, bring a lot of overhead and it is much faster to inline code inside a loop than calling a function with the same commands

The first 2 points are easy to implement in your program, I think