Add Produce A Lowercase V4 UUID as a Unix TIL

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

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+# 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.