jq – sed for JSON

I can’t remember the last time a day went by that I didn’t end up working with JSON data. It’s a lovely format to work with, but unfortunately due to how verbose it is it can be quite difficult to extract thespecific details that you’re looking for.

jq is a standalone binary for working with JSON. Just download it, put it in your $PATH and get tow ork. It has all kinds of options available, but I tend to use it just for filtering data.

My most common use case is this:

  echo '{"foo":"bar","bees":true}' | jq .

jq reads the JSON from stdin and runs the . filter (aka “match everything”) against it. This results
in a nicely formatted JSON representation for me to read.

Sometimes though, the output I’m using is a bit big to search through by hand. This is where jq filters come in useful. Using the same JSON as last time, I want to see the output of “foo”.

  echo '{"foo":"bar","bees":true}' | jq .foo

Things are starting to get a bit more complicated now, but still not too complicated that I couldn’t look at it by hand. Let’s take a look at what happens when we get arrays of data involved. We want to go through each array item and pull out “foo”. So, from our root (.), look at each array item ([]), and pull out “foo” (.foo). This makes our filter .[].foo.

  echo '[{"foo":"bar","bees":true},{"foo":"baz","bees":true},{"foo":"foo","bees":true},{"foo":"bee","bees":true}]' | jq ".[].foo"

That’s pretty much the extent of my experience with jq. There’s a whole host of advanced features that are explained well in the manual.

There’s plenty of ways to install jq – for most people it’s just a case of downloading the binary. If you’re on a Debian based OS it’s available in apt, or if you’re on OSX it’s on brew.

Michael is a polyglot software engineer, committed to reducing complexity in systems and making them more predictable. Working with a variety of languages and tools, he shares his technical expertise to audiences all around the world at user groups and conferences. You can follow @mheap on Twitter

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