til/jq/turn-a-list-from-a-command-into-json.md

Turn A List From A Command Into JSON

There are a lot of command-line utilities that produce a list of things. Since JSON is a universal data format, it would be useful to be able to quickly turn some items from stdout into a JSON list.

The jq utility can help with this.

Let's say I'm working with the following git command that lists changed files in a specific directory.

$ git diff --name-only | grep some/dir

I can then pipe that list of files to jq with a few flags.

$ git diff --name-only \
  | grep some/dir \
  | jq -R -s 'split("\n")[:-1]'

Here's what is going on:

• The -R flag tells jq to accept raw input, rather than looking for JSON.
• The -s flag is short for --slurp and tells jq to read in the entire input before applying the filter.
• The string argument is the filter to be applied to the output. It splits on newlines and then takes the entire array except for the last item ([:-1]) which would be an empty string for the trailing newline.
• jq automatically turns the whole thing into a formatted JSON list.