contrib: diffpatch.sh: validate arguments

contrib/diffpatch.sh

@@ -2,4 +2,11 @@
 # create a patch file based on file extension
 # $1 folder to run the find in
 # $2 extension to use for the diff
-find $1 -name "*$2" -exec bash -c 'filepath="$1" ; dir=$(dirname "$filepath") ; base=$(basename -s $2 "$filepath") ; diff -pur $filepath $dir/$base' -- {} $2 \;
+
+if [ "$#" -ne 2 ]; then
+    echo "expected two arguments" >&2
+    echo "usage: diffpatch.sh <package_folder> <file_extension_between_old_new_versions>" >&2
+    exit 2
+fi
+
+find $1 -name "*$2" -exec bash -c 'filepath="$1" ; dir=$(dirname "$filepath") ; base=$(basename -s $2 "$filepath") ; diff -pur $filepath $dir/$base' -- {} $2 \;