From fe60ffdfde90b4bbbd0ba570cd8a9b4282f4b7ac Mon Sep 17 00:00:00 2001
From: Jakob Kaivo <jkk@ung.org>
Date: Thu, 16 Jul 2020 15:53:41 -0400
Subject: initial implementation

---
 caesar.sh | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)
 create mode 100644 caesar.sh

diff --git a/caesar.sh b/caesar.sh
new file mode 100644
index 0000000..186891d
--- /dev/null
+++ b/caesar.sh
@@ -0,0 +1,25 @@
+number=13
+
+while getopts n: opt; do
+	case $opt in
+	n)	number=${OPTARG};;
+	?)	exit 1;;
+	esac
+done
+
+shift $((OPTIND - 1))
+
+if [ $# -ne 0 ]; then
+	printf 'usage: %s [-n number]\n' "$0"
+	printf '\t-n the number of characters to rotate (default 13)\n'
+	exit 1
+fi
+
+number=$((number % 26))
+A=$(printf '%d' 0$(printf '%o' \"A\"))
+FROM=$(printf '%o' $((A + number)))
+THRU=$(printf '%o' $((A + number - 1)))
+TRUPPER=$(printf '%b-ZA-%b\n' "\0${FROM}" "\0${THRU}")
+trlower=$(echo $TRUPPER | tr [[:upper:]] [[:lower:]])
+
+exec tr "A-Za-z" "${TRUPPER}${trlower}"
-- 
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