Add Transform Text To Lowercase as a Unix TIL

unix/transform-text-to-lowercase.md

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+# Transform Text To Lowercase
+
+I was reading through [`setup.sh` in
+dkarter/dotfiles](https://github.com/dkarter/dotfiles/blob/master/setup.sh#L7-L9)
+and noticed this function for converting a given bit of text to all lowercase
+letters.
+
+```bash
+lowercase() {
+  echo "$1" | sed "y/ABCDEFGHIJKLMNOPQRSTUVWXYZ/abcdefghijklmnopqrstuvwxyz/"
+}
+```
+
+It's an interesting use of `sed`, but it made me wonder if `tr` was a better
+tool for this job. I looked into it and `tr` is better suited to the task, more
+expressive, and also compatible across Mac and Linux.
+
+Here is what it looks like with `tr`:
+
+```bash
+lowercase() {
+  echo "$1" | tr '[:upper:]' '[:lower:]'
+}
+```
+
+This has the added benefit of working across all kinds of UTF-8 characters.
+
+```bash
+$ echo "ΑΛΦΑΒΗΤΟ ΕΛΛΑΔΑ" | tr '[:upper:]' '[:lower:]'
+αλφαβητο ελλαδα
+```
+
+See `man tr` for more details.