Add Produce A Lowercase V4 UUID as a Unix 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).
 
-_1334 TILs and counting..._
+_1335 TILs and counting..._
 
 ---
 
@@ -1322,6 +1322,7 @@ _1334 TILs and counting..._
 - [Print Milliseconds In Human-Readable Format](unix/print-milliseconds-in-human-readable-format.md)
 - [Print Out Files In Reverse](unix/print-out-files-in-reverse.md)
 - [Print The Current Date In Human-Readable Format](unix/print-the-current-date-in-human-readable-format.md)
+- [Produce A Lowercase V4 UUID](unix/produce-a-lowercase-v4-uuid.md)
 - [Provide A Fallback Value For Unset Parameter](unix/provide-a-fallback-value-for-unset-parameter.md)
 - [Remove A Directory Called `-p`](unix/remove-a-directory-called-dash-p.md)
 - [Repeat Yourself](unix/repeat-yourself.md)

unix/produce-a-lowercase-v4-uuid.md

@@ -0,0 +1,26 @@
+# Produce A Lowercase V4 UUID
+
+There are [a variety of ways to produce a v4
+UUID](different-ways-to-generate-a-v4-uuid.md) on Unix-based machines. Of the
+options I listed in that post, my favorite is the `uuidgen` command. My only
+gripe with it is that it produces an all uppercase UUID.
+
+```bash
+$ uuidgen
+B7918C26-12AE-4093-B6DA-0D7D41C59FB6
+```
+
+Often when I need a UUID, it is to plug in as the ID value for some test data
+in a system that is using lowercase UUIDs. For the sake of consistency, I'd
+like it to be lowercase as well.
+
+The `tr` command comes in handy for this because I can _tr_anslate the
+uppercase characters to lowercase ones.
+
+```bash
+$ uuidgen | tr '[:upper:]' '[:lower:]'
+ed817cf3-8f70-4838-82bc-8e5b328c0b93
+```
+
+So now anytime I need a lowercase UUID, I hit `ctrl-r` and search back for
+either `uuid` or `lower` and find this command pretty quickly.