@@ -21,6 +21,7 @@ git refs list [--count=<count>] [--shell|--perl|--python|--tcl]
 git refs exists <ref>
 git refs optimize [--all] [--no-prune] [--auto] [--include <pattern>] [--exclude <pattern>]
 git refs delete [--message=<reason>] [--no-deref] <ref> [<old-value>]
+git refs update [--message=<reason>] [--no-deref] [--create-reflog] <ref> <new-value> [<old-value>]
 
 DESCRIPTION
 -----------

@@ -58,6 +59,13 @@ delete::
 	reference is only deleted after verifying that it currently contains
 	`<old-value>`.
 
+update::
+	Update the given reference to point at `<new-value>`. If `<old-value>`
+	is given, the reference is only updated after verifying that it
+	currently contains `<old-value>`. As a special case, an all-zeroes
+	`<new-value>` deletes the branch, whereas an all-zeroes `<old-value>`
+	ensures that the branch does not yet exist.
+
 OPTIONS
 -------
 

@@ -99,6 +107,10 @@ include::pack-refs-options.adoc[]
 
 The following options are specific to commands which write references:
 
+`--create-reflog`::
+	Create a reflog for the reference even if one would not ordinarily be
+	created.
+
 `--message=<reason>`::
 	Use the given <reason> string for the reflog entry associated with the
 	update. An empty message is rejected.

@@ -24,6 +24,9 @@
 #define REFS_DELETE_USAGE \
 	N_("git refs delete [--message=<reason>] [--no-deref] <ref> [<old-value>]")
 
+#define REFS_UPDATE_USAGE \
+	N_("git refs update [--message=<reason>] [--no-deref] [--create-reflog] <ref> <new-value> [<old-value>]")
+
 static int cmd_refs_migrate(int argc, const char **argv, const char *prefix,
 			    struct repository *repo)
 {

@@ -224,6 +227,56 @@ static int cmd_refs_delete(int argc, const char **argv, const char *prefix,
 	return ret;
 }
 
+static int cmd_refs_update(int argc, const char **argv, const char *prefix,
+			   struct repository *repo)
+{
+	static char const * const refs_update_usage[] = {
+		REFS_UPDATE_USAGE,
+		NULL
+	};
+	const char *message = NULL;
+	unsigned flags = 0;
+	struct option opts[] = {
+		OPT_STRING(0, "message", &message, N_("reason"),
+			   N_("reason of the update")),
+		OPT_BIT(0 ,"no-deref", &flags,
+			N_("update <refname> not the one it points to"),
+			REF_NO_DEREF),
+		OPT_BIT(0, "create-reflog", &flags, N_("create a reflog"),
+			REF_FORCE_CREATE_REFLOG),
+		OPT_END(),
+	};
+	struct object_id newoid, oldoid;
+	const char *refname;
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, opts, refs_update_usage, 0);
+	if (argc < 2 || argc > 3)
+		usage(_("update requires reference name, new value and an optional old value"));
+
+	if (message && !*message)
+		die(_("refusing to perform update with empty message"));
+
+	repo_config(repo, git_default_config, NULL);
+
+	refname = argv[0];
+	if (repo_get_oid_with_flags(repo, argv[1], &newoid,
+				    GET_OID_SKIP_AMBIGUITY_CHECK))
+		die(_("invalid new object ID: '%s'"), argv[1]);
+	if (argc == 3 &&
+	    repo_get_oid_with_flags(repo, argv[2], &oldoid,
+				    GET_OID_SKIP_AMBIGUITY_CHECK))
+		die(_("invalid old object ID: '%s'"), argv[2]);
+
+	ret = refs_update_ref(get_main_ref_store(repo), message, refname,
+			      &newoid, argc == 3 ? &oldoid : NULL, flags,
+			      UPDATE_REFS_MSG_ON_ERR);
+
+	if (ret < 0)
+		ret = 1;
+	return ret;
+}
+
 int cmd_refs(int argc,
 	     const char **argv,
 	     const char *prefix,

@@ -236,6 +289,7 @@ int cmd_refs(int argc,
 		REFS_EXISTS_USAGE,
 		REFS_OPTIMIZE_USAGE,
 		REFS_DELETE_USAGE,
+		REFS_UPDATE_USAGE,
 		NULL,
 	};
 	parse_opt_subcommand_fn *fn = NULL;

@@ -246,6 +300,7 @@ int cmd_refs(int argc,
 		OPT_SUBCOMMAND("exists", &fn, cmd_refs_exists),
 		OPT_SUBCOMMAND("optimize", &fn, cmd_refs_optimize),
 		OPT_SUBCOMMAND("delete", &fn, cmd_refs_delete),
+		OPT_SUBCOMMAND("update", &fn, cmd_refs_update),
 		OPT_END(),
 	};
 

@@ -224,6 +224,7 @@ integration_tests = [
   't1462-refs-exists.sh',
   't1463-refs-optimize.sh',
   't1464-refs-delete.sh',
+  't1465-refs-update.sh',
   't1500-rev-parse.sh',
   't1501-work-tree.sh',
   't1502-rev-parse-parseopt.sh',

@@ -0,0 +1,268 @@
+#!/bin/sh
+
+test_description='git refs update'
+
+. ./test-lib.sh
+
+setup_repo () {
+	git init "$1" &&
+	test_commit -C "$1" A &&
+	test_commit -C "$1" B
+}
+
+test_ref_matches () {
+	git rev-parse "$1" >expect &&
+	echo "$2" >actual &&
+	test_cmp expect actual
+}
+
+test_expect_success 'update creates a new reference' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		git refs update refs/heads/foo $A &&
+		test_ref_matches refs/heads/foo "$A"
+	)
+'
+
+test_expect_success 'update an existing reference without oldvalue' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		B=$(git rev-parse B) &&
+		git refs update refs/heads/foo $A &&
+		git refs update refs/heads/foo $B &&
+		test_ref_matches refs/heads/foo $B
+	)
+'
+
+test_expect_success 'update with matching oldvalue' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		B=$(git rev-parse B) &&
+		git refs update refs/heads/foo $A &&
+		git refs update refs/heads/foo $B $A &&
+		test_ref_matches refs/heads/foo $B
+	)
+'
+
+test_expect_success 'update with stale oldvalue fails' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		B=$(git rev-parse B) &&
+		git refs update refs/heads/foo $A &&
+		test_must_fail git refs update refs/heads/foo $B $B 2>err &&
+		test_grep " but expected " err &&
+		test_ref_matches refs/heads/foo $A
+	)
+'
+
+test_expect_success 'update can create a new branch with oldvalue' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		git refs update refs/heads/foo $A $ZERO_OID 2>err &&
+		test_ref_matches refs/heads/foo $A
+	)
+'
+
+test_expect_success 'update can create a new branch without oldvalue' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		git refs update refs/heads/foo $A 2>err &&
+		test_ref_matches refs/heads/foo $A
+	)
+'
+
+test_expect_success 'update refuses to create preexisting branch' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		B=$(git rev-parse B) &&
+		git refs update refs/heads/foo $A &&
+		test_must_fail git refs update refs/heads/foo $B $ZERO_OID 2>err &&
+		test_grep "reference already exists" err &&
+		test_ref_matches refs/heads/foo $A
+	)
+'
+
+test_expect_success 'update can delete a branch with oldvalue' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		git refs update refs/heads/foo $A 2>err &&
+		git refs update refs/heads/foo $ZERO_OID $A 2>err &&
+		test_must_fail git refs exists refs/heads/foo
+	)
+'
+
+test_expect_success 'update can delete a branch without oldvalue' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		git refs update refs/heads/foo $A 2>err &&
+		git refs update refs/heads/foo $ZERO_OID 2>err &&
+		test_must_fail git refs exists refs/heads/foo
+	)
+'
+
+test_expect_success 'update refuses to delete a branch with mismatching value' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		B=$(git rev-parse B) &&
+		git refs update refs/heads/foo $A 2>err &&
+		test_must_fail git refs update refs/heads/foo $ZERO_OID $B 2>err &&
+		test_grep " but expected " err &&
+		git refs exists refs/heads/foo
+	)
+'
+
+test_expect_success 'update refuses to create preexisting branch' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		B=$(git rev-parse B) &&
+		git refs update refs/heads/foo $A &&
+		test_must_fail git refs update refs/heads/foo $B $ZERO_OID 2>err &&
+		test_grep "reference already exists" err &&
+		test_ref_matches refs/heads/foo $A
+	)
+'
+
+
+test_expect_success 'update with invalid new value fails' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		test_must_fail git refs update refs/heads/foo invalid-oid 2>err &&
+		test_grep "invalid new object ID" err &&
+		test_must_fail git refs exists refs/heads/foo
+	)
+'
+
+test_expect_success 'update with invalid old value fails' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		B=$(git rev-parse B) &&
+		git refs update refs/heads/foo $A &&
+		test_must_fail git refs update refs/heads/foo $B invalid-oid 2>err &&
+		test_grep "invalid old object ID" err &&
+		test_ref_matches refs/heads/foo $A
+	)
+'
+
+test_expect_success 'update --no-deref rewrites the symref itself' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		B=$(git rev-parse B) &&
+		git refs update refs/heads/foo $A &&
+		git symbolic-ref refs/heads/symref refs/heads/foo &&
+		git refs update --no-deref refs/heads/symref $B &&
+		test_must_fail git symbolic-ref refs/heads/symref &&
+		test_ref_matches refs/heads/symref $B &&
+		test_ref_matches refs/heads/foo $A
+	)
+'
+
+test_expect_success 'update does not create a reflog by default' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		git refs update refs/foo $A &&
+		test_must_fail git reflog exists refs/foo
+	)
+'
+
+test_expect_success 'update creates a reflog with --create-reflog' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		git refs update --create-reflog refs/foo $A &&
+		git reflog exists refs/foo
+	)
+'
+
+test_expect_success 'update with message records reason in reflog' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		B=$(git rev-parse B) &&
+		git refs update refs/heads/foo $A &&
+		git refs update --message=update-reason refs/heads/foo $B &&
+		git reflog show refs/heads/foo >actual &&
+		test_grep "update-reason$" actual
+	)
+'
+
+test_expect_success 'update with empty message fails' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		B=$(git rev-parse B) &&
+		git refs update refs/heads/foo $A &&
+		test_must_fail git refs update --message= refs/heads/foo $B 2>err &&
+		test_grep "empty message" err
+	)
+'
+
+test_expect_success 'update with too few arguments fails' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	test_must_fail git -C repo refs update refs/heads/foo 2>err &&
+	test_grep "requires reference name, new value" err
+'
+
+test_expect_success 'update with too many arguments fails' '
+	test_when_finished "rm -rf repo" &&
+	setup_repo repo &&
+	(
+		cd repo &&
+		A=$(git rev-parse A) &&
+		B=$(git rev-parse B) &&
+		test_must_fail git refs update refs/heads/foo $A $B extra 2>err &&
+		test_grep "requires reference name, new value" err
+	)
+'
+
+test_done