[New Blog Post] Surely you're jqing

[stochastical]

Blog Post Title

Surely you're jqing

Blog Section

Microblog

Post Date

2025-02-18

Description

Learning jq by reading the manual end-to-end.

Link

https://jqlang.org/manual/

Additional Content

Today I read through the jq manual cover-to-cover. For those unaware, jq is a popular CLI tool to query and manipulate JSON. It's a mini-language with nice functional semantics and fits into the ethos of composable CLI tools.

It was an exemplar of well-written technical documentation. Concise, well-written, littered with examples, and linking to an interactive playground to test-and-learn.

Some learnings:

1. It's surprisingly functional! You can implement recursive functions and use higher-order functions! For example, here's factorial in jq:

jq '[.,1]|until(.[0] < 1; [.[0] - 1, .[1] * .[0]])|.[1]'

2. It supports string interpolation - this is really nice if you're piping stuff from JSON into a string. Coupled with format strings this becomes frictionless:

$ echo '{"search":"hello; world"}' | jq -r '@uri "https://www.google.com/search?q=\(.search)"'
# https://www.google.com/search?q=hello%3B%20world

3. You can define functions that accept functions¹, and control structures that allow labelling.

echo '[[1,2],[10,20]]' | jq -r 'def addvalue(f): . + [f]; map(addvalue(.[0]))'
[[1,2,1], [10,20,10]]

4. You can traverse complex data structures with first-class pathing support. And you can easily modify nested structures to extend objects.

Side note: This is one of my goals for 2025 - read through documentation end-to-end to develop mastery over tools. I'm trying to prioritise selectively depth over breadth.

Footnotes

1. The line between "functions" and "filters" is a little blurry to me. ↩

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