t7800-difftool.sh: Simplify the --extcmd test

diff --git a/show-index.c b/show-index.c
index 45bb535773fd9c36f73502df9462f7de800009c8..63f9da53237d4233bede66a28e4bcf27d5b44af1 100644 (file)
--- a/show-index.c
+++ b/show-index.c
@@ -1,6 +1,9 @@
 #include "cache.h"
 #include "pack.h"
 
+static const char show_index_usage[] =
+"git show-index < <packed archive index>";
+
 int main(int argc, char **argv)
 {
        int i;
@@ -8,6 +11,8 @@ int main(int argc, char **argv)
        unsigned int version;
        static unsigned int top_index[256];
 
+       if (argc != 1)
+               usage(show_index_usage);
        if (fread(top_index, 2 * 4, 1, stdin) != 1)
                die("unable to read header");
        if (top_index[0] == htonl(PACK_IDX_SIGNATURE)) {