1 files changed, 76 insertions, 14 deletions

diff --git a/builtin-grep.c b/builtin-grep.c
index e13cb31f2b..c7b45c4d58 100644
--- a/builtin-grep.c
+++ b/builtin-grep.c
@@ -187,6 +187,78 @@ static int exec_grep(int argc, const char **argv)
 	else die("maximum number of args exceeded"); \
 	} while (0)
 
+/*
+ * If you send a singleton filename to grep, it does not give
+ * the name of the file.  GNU grep has "-H" but we would want
+ * that behaviour in a portable way.
+ *
+ * So we keep two pathnames in argv buffer unsent to grep in
+ * the main loop if we need to do more than one grep.
+ */
+static int flush_grep(struct grep_opt *opt,
+		      int argc, int arg0, const char **argv, int *kept)
+{
+	int status;
+	int count = argc - arg0;
+	const char *kept_0 = NULL;
+
+	if (count <= 2) {
+		/*
+		 * Because we keep at least 2 paths in the call from
+		 * the main loop (i.e. kept != NULL), and MAXARGS is
+		 * far greater than 2, this usually is a call to
+		 * conclude the grep.  However, the user could attempt
+		 * to overflow the argv buffer by giving too many
+		 * options to leave very small number of real
+		 * arguments even for the call in the main loop.
+		 */
+		if (kept)
+			die("insanely many options to grep");
+
+		/*
+		 * If we have two or more paths, we do not have to do
+		 * anything special, but we need to push /dev/null to
+		 * get "-H" behaviour of GNU grep portably but when we
+		 * are not doing "-l" nor "-L" nor "-c".
+		 */
+		if (count == 1 &&
+		    !opt->name_only &&
+		    !opt->unmatch_name_only &&
+		    !opt->count) {
+			argv[argc++] = "/dev/null";
+			argv[argc] = NULL;
+		}
+	}
+
+	else if (kept) {
+		/*
+		 * Called because we found many paths and haven't finished
+		 * iterating over the cache yet.  We keep two paths
+		 * for the concluding call.  argv[argc-2] and argv[argc-1]
+		 * has the last two paths, so save the first one away,
+		 * replace it with NULL while sending the list to grep,
+		 * and recover them after we are done.
+		 */
+		*kept = 2;
+		kept_0 = argv[argc-2];
+		argv[argc-2] = NULL;
+		argc -= 2;
+	}
+
+	status = exec_grep(argc, argv);
+
+	if (kept_0) {
+		/*
+		 * Then recover them.  Now the last arg is beyond the
+		 * terminating NULL which is at argc, and the second
+		 * from the last is what we saved away in kept_0
+		 */
+		argv[arg0++] = kept_0;
+		argv[arg0] = argv[argc+1];
+	}
+	return status;
+}
+
 static int external_grep(struct grep_opt *opt, const char **paths, int cached)
 {
 	int i, nr, argc, hit, len, status;
@@ -253,22 +325,12 @@ static int external_grep(struct grep_opt *opt, const char **paths, int cached)
 		push_arg(p->pattern);
 	}
 
-	/*
-	 * To make sure we get the header printed out when we want it,
-	 * add /dev/null to the paths to grep.  This is unnecessary
-	 * (and wrong) with "-l" or "-L", which always print out the
-	 * name anyway.
-	 *
-	 * GNU grep has "-H", but this is portable.
-	 */
-	if (!opt->name_only && !opt->unmatch_name_only)
-		push_arg("/dev/null");
-
 	hit = 0;
 	argc = nr;
 	for (i = 0; i < active_nr; i++) {
 		struct cache_entry *ce = active_cache[i];
 		char *name;
+		int kept;
 		if (!S_ISREG(ntohl(ce->ce_mode)))
 			continue;
 		if (!pathspec_matches(paths, ce->name))
@@ -283,10 +345,10 @@ static int external_grep(struct grep_opt *opt, const char **paths, int cached)
 		argv[argc++] = name;
 		if (argc < MAXARGS && !ce_stage(ce))
 			continue;
-		status = exec_grep(argc, argv);
+		status = flush_grep(opt, argc, nr, argv, &kept);
 		if (0 < status)
 			hit = 1;
-		argc = nr;
+		argc = nr + kept;
 		if (ce_stage(ce)) {
 			do {
 				i++;
@@ -296,7 +358,7 @@ static int external_grep(struct grep_opt *opt, const char **paths, int cached)
 		}
 	}
 	if (argc > nr) {
-		status = exec_grep(argc, argv);
+		status = flush_grep(opt, argc, nr, argv, NULL);
 		if (0 < status)
 			hit = 1;
 	}