Merge pull request #552 from crawford/core_date

core_date: add help message

core_date

@@ -7,7 +7,29 @@
 SCRIPT_ROOT=$(dirname $(readlink -f "$0"))
 . "${SCRIPT_ROOT}/common.sh" || exit 1
 
-if [[ "$1" == "-v" ]]; then
+USAGE="USAGE: $0 [-v] [date flags]
+
+This script calculates the date given the CoreOS major version or calculates
+the version given a date.
+
+Examples:
+
+  $0 -v 1000
+  Sun Mar 27 00:00:00 UTC 2016
+
+  $0 -v 1000 --iso-8601
+  2016-03-27
+
+  $0 --date 'Jun 1, 2016'
+  1066
+"
+
+case "$1" in
+    "-h")
+        echo "$USAGE"
+        ;;
+
+    "-v")
         shift
         if [[ $# -ge 1 ]] && [[ "$1" != [-+]* ]]; then
             v="$1"
@@ -22,7 +44,10 @@ if [[ "$1" == "-v" ]]; then
 
         export TZ=${TZ:=UTC}
         date -d @$(( (v * 86400) + COREOS_EPOCH )) "$@"
-else
+        ;;
+
+    *)
         t=$(date +%s "$@")
         echo $(( (t - COREOS_EPOCH) / 86400 ))
-fi
+        ;;
+esac