mbr_dump.sh: should check script arguments better

diff --git a/mbr_dump.sh b/mbr_dump.sh
index dce7962..d97e450 100755 (executable)
--- a/mbr_dump.sh
+++ b/mbr_dump.sh
@@ -6,14 +6,22 @@
 #
 # Colin McCabe
 #
+usage() {
+       echo "usage: ${0} <IBM-master-boot-record>"
+       echo "should be 512 bytes in length."
+       exit 1
+}
+
+if [ $# -ne 1 ]; then
+       usage
+fi
 
 if [ -e ${1} ]; then
        PART_FILE=${1}
 else
-       echo "usage: ${0} <IBM-master-boot-record>"
-       echo "should be 512 bytes in length."
-       exit 1
+       usage
 fi
+
 echo "# first partition"
 od -j 446 -N 16 -t x1 ${1}
 echo "# second partition"