1 files changed, 59 insertions, 0 deletions
diff --git a/builtin-update-ref.c b/builtin-update-ref.c
new file mode 100644
index 0000000000..00333c7e7c
--- /dev/null
+++ b/builtin-update-ref.c
@@ -0,0 +1,59 @@
+#include "cache.h"
+#include "refs.h"
+#include "builtin.h"
+
+static const char git_update_ref_usage[] =
+"git-update-ref <refname> <value> [<oldval>] [-m <reason>]";
+
+int cmd_update_ref(int argc, const char **argv, char **envp)
+{
+	const char *refname=NULL, *value=NULL, *oldval=NULL, *msg=NULL;
+	struct ref_lock *lock;
+	unsigned char sha1[20], oldsha1[20];
+	int i;
+
+	setup_git_directory();
+	git_config(git_default_config);
+
+	for (i = 1; i < argc; i++) {
+		if (!strcmp("-m", argv[i])) {
+			if (i+1 >= argc)
+				usage(git_update_ref_usage);
+			msg = argv[++i];
+			if (!*msg)
+				die("Refusing to perform update with empty message.");
+			if (strchr(msg, '\n'))
+				die("Refusing to perform update with \\n in message.");
+			continue;
+		}
+		if (!refname) {
+			refname = argv[i];
+			continue;
+		}
+		if (!value) {
+			value = argv[i];
+			continue;
+		}
+		if (!oldval) {
+			oldval = argv[i];
+			continue;
+		}
+	}
+	if (!refname || !value)
+		usage(git_update_ref_usage);
+
+	if (get_sha1(value, sha1))
+		die("%s: not a valid SHA1", value);
+	memset(oldsha1, 0, 20);
+	if (oldval && get_sha1(oldval, oldsha1))
+		die("%s: not a valid old SHA1", oldval);
+
+	lock = lock_any_ref_for_update(refname, oldval ? oldsha1 : NULL, 0);
+	if (!lock)
+		return 1;
+	if (write_ref_sha1(lock, sha1, msg) < 0)
+		return 1;
+
+	/* write_ref_sha1 always unlocks the ref, no need to do it explicitly */
+	return 0;
+}