Add Turn A List From A Command Into JSON as a jq TIL

Author: jbranchaud

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1340 TILs and counting..._
+_1341 TILs and counting..._
 
 ---
 
@@ -500,6 +500,7 @@ _1340 TILs and counting..._
 - [Find All Objects With A Matching Key Value Pair](jq/find-all-objects-with-a-matching-key-value-pair.md)
 - [Get The First Item For Every Top-Level Key](jq/get-the-first-item-for-every-top-level-key.md)
 - [Reduce Object To Just Entries Of A Specific Type](jq/reduce-object-to-just-entries-of-a-specific-type.md)
+- [Turn A List From A Command Into JSON](jq/turn-a-list-from-a-command-into-json.md)
 
 ### Kitty
 

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

@@ -0,0 +1,32 @@
+# 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`](https://jqlang.github.io/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.
+
+```bash
+$ git diff --name-only | grep some/dir
+```
+
+I can then pipe that list of files to `jq` with a few flags.
+
+```bash
+$ 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.