x-dpi-facesizes.sh: support an optional paramter

utils/scripts/x-dpi-facesizes.sh

@@ -10,11 +10,22 @@
 # Dedication along with this software. If not, see
 # <http://creativecommons.org/publicdomain/zero/1.0/>.
 
+usage()
+{
+	printf "Usage: %s [targetdpi]\n" "${0##*/}" >&2
+	exit 1
+}
+
+if [ $# -gt 1 ]; then
+	usage
+fi
+
 FACESIZES="10.5 6.0 8.0 9.0 10.5 12.0 18.0"
 BASEDPI=96
 
-targetdpi=96
-if command -v xdpyinfo >/dev/null 2>&1; then
+if [ -n "$1" ]; then
+	targetdpi=$1
+elif command -v xdpyinfo >/dev/null 2>&1; then
 	targetdpi=$(xdpyinfo | grep '^  resolution:' | {
 		min=
 		while read -r line; do
@@ -29,13 +40,12 @@ if command -v xdpyinfo >/dev/null 2>&1; then
 			fi
 		done
 
-		if [ -z "$min" ]; then
-			echo 96
-		else
+		if [ -n "$min" ]; then
 			echo "$min / 2" | bc -l
 		fi
 	})
 fi
+: ${targetdpi:=96}
 
 for facesize in $FACESIZES; do
 	echo "$BASEDPI * $facesize / $targetdpi"