1 files changed, 9 insertions, 3 deletions
diff --git a/aux/lib.sh b/aux/lib.sh
index 52f1315..e345bd6 100644
--- a/aux/lib.sh
+++ b/aux/lib.sh
@@ -1,8 +1,14 @@
 #!/bin/sh
 
-#
-# Generally, utilities that I expected to exist in POSIX, but don't.
-#
+assert_arg() {
+	if [ -z "$1" ]; then
+		printf 'Missing %s.\n\n' "$2" >&2
+		cat <<-'EOF'
+			usage >&2
+			exit 2
+		EOF
+	fi
+}
 
 uuid() {
 	od -xN20 /dev/urandom |