rev-parse: --local-env-vars option

This prints the list of repo-local environment variables.
Signed-off-by: NGiuseppe Bilotta <giuseppe.bilotta@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-rev-parse.txt

@@ -149,6 +149,12 @@ shown.  If the pattern does not contain a globbing character (`?`,
 --is-bare-repository::
 	When the repository is bare print "true", otherwise "false".
 
+--local-env-vars::
+	List the GIT_* environment variables that are local to the
+	repository (e.g. GIT_DIR or GIT_WORK_TREE, but not GIT_EDITOR).
+	Only the names of the variables are listed, not their value,
+	even if they are set.
+
 --short::
 --short=number::
 	Instead of outputting the full SHA1 values of object names try to

builtin-rev-parse.c

@@ -455,6 +455,13 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 	if (argc > 1 && !strcmp("--sq-quote", argv[1]))
 		return cmd_sq_quote(argc - 2, argv + 2);
 
+	if (argc == 2 && !strcmp("--local-env-vars", argv[1])) {
+		int i;
+		for (i = 0; local_repo_env[i]; i++)
+			printf("%s\n", local_repo_env[i]);
+		return 0;
+	}
+
 	if (argc > 1 && !strcmp("-h", argv[1]))
 		usage(builtin_rev_parse_usage);