patch, 11 parts[RFC] config-batch: a new builtin for tools querying config

.gitignore, Documentation/git-config-batch.adoc, Documentation/meson.build, Makefile, builtin.h, builtin/config-batch.c, command-list.txt, git.c, meson.build, t/meson.build, t/t1312-config-batch.sh

diff --git a/.gitignore b/.gitignore
index 78a45cb5be..42640b5e24 100644
--- a/.gitignore
+++ b/.gitignore
@@ -44,6 +44,7 @@
 /git-commit-graph
 /git-commit-tree
 /git-config
+/git-config-batch
 /git-count-objects
 /git-credential
 /git-credential-cache
diff --git a/Documentation/git-config-batch.adoc b/Documentation/git-config-batch.adoc
new file mode 100644
index 0000000000..dfa0bd83e2
--- /dev/null
+++ b/Documentation/git-config-batch.adoc
@@ -0,0 +1,24 @@
+git-config-batch(1)
+===================
+
+NAME
+----
+git-config-batch - Get and set options using machine-parseable interface
+
+
+SYNOPSIS
+--------
+[verse]
+'git config-batch' <options>
+
+DESCRIPTION
+-----------
+TODO
+
+SEE ALSO
+--------
+linkgit:git-config[1]
+
+GIT
+---
+Part of the linkgit:git[1] suite
diff --git a/Documentation/meson.build b/Documentation/meson.build
index f02dbc20cb..f5ad117921 100644
--- a/Documentation/meson.build
+++ b/Documentation/meson.build
@@ -29,6 +29,7 @@ manpages = {
   'git-commit-tree.adoc' : 1,
   'git-commit.adoc' : 1,
   'git-config.adoc' : 1,
+  'git-config-batch.adoc' : 1,
   'git-count-objects.adoc' : 1,
   'git-credential-cache--daemon.adoc' : 1,
   'git-credential-cache.adoc' : 1,
diff --git a/Makefile b/Makefile
index 8aa489f3b6..aa3868e513 100644
--- a/Makefile
+++ b/Makefile
@@ -1390,6 +1390,7 @@ BUILTIN_OBJS += builtin/commit-graph.o
 BUILTIN_OBJS += builtin/commit-tree.o
 BUILTIN_OBJS += builtin/commit.o
 BUILTIN_OBJS += builtin/config.o
+BUILTIN_OBJS += builtin/config-batch.o
 BUILTIN_OBJS += builtin/count-objects.o
 BUILTIN_OBJS += builtin/credential-cache--daemon.o
 BUILTIN_OBJS += builtin/credential-cache.o
diff --git a/builtin.h b/builtin.h
index e5e16ecaa6..5f5a19635e 100644
--- a/builtin.h
+++ b/builtin.h
@@ -68,12 +68,18 @@
  *
  * . Add `builtin/foo.o` to `BUILTIN_OBJS` in `Makefile`.
  *
+ * . Add 'builtin/foo.c' to the 'builtin_sources' array in 'meson.build'.
+ *
  * Additionally, if `foo` is a new command, there are 4 more things to do:
  *
  * . Add tests to `t/` directory.
  *
+ * . Add the test script to 'integration_tests' in  't/meson.build'.
+ *
  * . Write documentation in `Documentation/git-foo.adoc`.
  *
+ * . Add 'git-foo.adoc' to the manpages list in 'Documentation/meson.build'.
+ *
  * . Add an entry for `git-foo` to `command-list.txt`.
  *
  * . Add an entry for `/git-foo` to `.gitignore`.
@@ -167,6 +173,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix, struct repositor
 int cmd_commit_graph(int argc, const char **argv, const char *prefix, struct repository *repo);
 int cmd_commit_tree(int argc, const char **argv, const char *prefix, struct repository *repo);
 int cmd_config(int argc, const char **argv, const char *prefix, struct repository *repo);
+int cmd_config_batch(int argc, const char **argv, const char *prefix, struct repository *repo);
 int cmd_count_objects(int argc, const char **argv, const char *prefix, struct repository *repo);
 int cmd_credential(int argc, const char **argv, const char *prefix, struct repository *repo);
 int cmd_credential_cache(int argc, const char **argv, const char *prefix, struct repository *repo);
diff --git a/builtin/config-batch.c b/builtin/config-batch.c
new file mode 100644
index 0000000000..ea4f408ecb
--- /dev/null
+++ b/builtin/config-batch.c
@@ -0,0 +1,30 @@
+#define USE_THE_REPOSITORY_VARIABLE
+#include "builtin.h"
+#include "config.h"
+#include "environment.h"
+#include "parse-options.h"
+
+static const char *const builtin_config_batch_usage[] = {
+	N_("git config-batch <options>"),
+	NULL
+};
+
+int cmd_config_batch(int argc,
+		     const char **argv,
+		     const char *prefix,
+		     struct repository *repo)
+{
+	struct option options[] = {
+		OPT_END(),
+	};
+
+	show_usage_with_options_if_asked(argc, argv,
+					 builtin_config_batch_usage, options);
+
+	argc = parse_options(argc, argv, prefix, options, builtin_config_batch_usage,
+			     0);
+
+	repo_config(repo, git_default_config, NULL);
+
+	return 0;
+}
diff --git a/command-list.txt b/command-list.txt
index accd3d0c4b..57c7c7458d 100644
--- a/command-list.txt
+++ b/command-list.txt
@@ -83,6 +83,7 @@ git-commit                              mainporcelain           history
 git-commit-graph                        plumbingmanipulators
 git-commit-tree                         plumbingmanipulators
 git-config                              ancillarymanipulators           complete
+git-config-batch                        plumbinginterrogators
 git-count-objects                       ancillaryinterrogators
 git-credential                          purehelpers
 git-credential-cache                    purehelpers
diff --git a/git.c b/git.c
index c5fad56813..6b55a867dd 100644
--- a/git.c
+++ b/git.c
@@ -557,6 +557,7 @@ static struct cmd_struct commands[] = {
 	{ "commit-graph", cmd_commit_graph, RUN_SETUP },
 	{ "commit-tree", cmd_commit_tree, RUN_SETUP },
 	{ "config", cmd_config, RUN_SETUP_GENTLY | DELAY_PAGER_CONFIG },
+	{ "config-batch", cmd_config_batch, RUN_SETUP_GENTLY },
 	{ "count-objects", cmd_count_objects, RUN_SETUP },
 	{ "credential", cmd_credential, RUN_SETUP_GENTLY | NO_PARSEOPT },
 	{ "credential-cache", cmd_credential_cache },
diff --git a/meson.build b/meson.build
index dd52efd1c8..040bc32c2d 100644
--- a/meson.build
+++ b/meson.build
@@ -582,6 +582,7 @@ builtin_sources = [
   'builtin/commit-tree.c',
   'builtin/commit.c',
   'builtin/config.c',
+  'builtin/config-batch.c',
   'builtin/count-objects.c',
   'builtin/credential-cache--daemon.c',
   'builtin/credential-cache.c',
diff --git a/t/meson.build b/t/meson.build
index 459c52a489..0e9f1826f8 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -186,6 +186,7 @@ integration_tests = [
   't1309-early-config.sh',
   't1310-config-default.sh',
   't1311-config-optional.sh',
+  't1312-config-batch.sh',
   't1350-config-hooks-path.sh',
   't1400-update-ref.sh',
   't1401-symbolic-ref.sh',
diff --git a/t/t1312-config-batch.sh b/t/t1312-config-batch.sh
new file mode 100755
index 0000000000..f59ba4a0f3
--- /dev/null
+++ b/t/t1312-config-batch.sh
@@ -0,0 +1,12 @@
+#!/bin/sh
+
+test_description='Test git config-batch'
+
+. ./test-lib.sh
+
+test_expect_success 'help text' '
+	test_must_fail git config-batch -h >out &&
+	grep usage out
+'
+
+test_done

Documentation/git-config-batch.adoc, builtin/config-batch.c, t/t1312-config-batch.sh

diff --git a/Documentation/git-config-batch.adoc b/Documentation/git-config-batch.adoc
index dfa0bd83e2..9ca04b0c1e 100644
--- a/Documentation/git-config-batch.adoc
+++ b/Documentation/git-config-batch.adoc
@@ -13,7 +13,28 @@ SYNOPSIS
 
 DESCRIPTION
 -----------
-TODO
+Tools frequently need to change their behavior based on values stored in
+Git's configuration files. These files may have complicated conditions
+for including extra files, so it is difficult to produce an independent
+parser. To avoid executing multiple processes to discover or modify
+multiple configuration values, the `git config-batch` command allows a
+single process to handle multiple requests using a machine-parseable
+interface across `stdin` and `stdout`.
+
+PROTOCOL
+--------
+By default, the protocol uses line feeds (`LF`) to signal the end of a
+command over `stdin` or a response over `stdout`.
+
+The protocol will be extended in the future, and consumers should be
+resilient to older Git versions not understanding the latest command
+set. Thus, if the Git version includes the `git config-batch` builtin
+but doesn't understand an input command, it will return a single line
+response:
+
+```
+unknown_command LF
+```
 
 SEE ALSO
 --------
diff --git a/builtin/config-batch.c b/builtin/config-batch.c
index ea4f408ecb..dffedb8ca2 100644
--- a/builtin/config-batch.c
+++ b/builtin/config-batch.c
@@ -3,17 +3,144 @@
 #include "config.h"
 #include "environment.h"
 #include "parse-options.h"
+#include "strbuf.h"
+#include "string-list.h"
 
 static const char *const builtin_config_batch_usage[] = {
 	N_("git config-batch <options>"),
 	NULL
 };
 
+#define UNKNOWN_COMMAND "unknown_command"
+
+static int emit_response(const char *response, ...)
+{
+	va_list params;
+	const char *token;
+
+	printf("%s", response);
+
+	va_start(params, response);
+	while ((token = va_arg(params, const char *)))
+		printf(" %s", token);
+	va_end(params);
+
+	printf("\n");
+	fflush(stdout);
+	return 0;
+}
+
+/**
+ * A function pointer type for defining a command. The function is
+ * responsible for handling different versions of the command name.
+ *
+ * Provides the remaining 'data' for the command, to be parsed by
+ * the function as needed according to its parsing rules.
+ *
+ * These functions should only return a negative value if they result
+ * in such a catastrophic failure that the process should end.
+ *
+ * Return 0 on success.
+ */
+typedef int (*command_fn)(struct repository *repo,
+			  char *data, size_t data_len);
+
+static int unknown_command(struct repository *repo UNUSED,
+			  char *data UNUSED, size_t data_len UNUSED)
+{
+	return emit_response(UNKNOWN_COMMAND, NULL);
+}
+
+struct command {
+	const char *name;
+	command_fn fn;
+	int version;
+};
+
+static struct command commands[] = {
+	/* unknown_command must be last. */
+	{
+		.name = "",
+		.fn   = unknown_command,
+	},
+};
+
+#define COMMAND_COUNT ((size_t)(sizeof(commands) / sizeof(*commands)))
+
+/**
+ * Process a single line from stdin and process the command.
+ *
+ * Returns 0 on successful processing of command, including the
+ * unknown_command output.
+ *
+ * Returns 1 on natural exit due to exist signal of empty line.
+ *
+ * Returns negative value on other catastrophic error.
+ */
+static int process_command(struct repository *repo)
+{
+	static struct strbuf line = STRBUF_INIT;
+	struct string_list tokens = STRING_LIST_INIT_NODUP;
+	const char *command;
+	int version;
+	char *data = NULL;
+	size_t data_len = 0;
+	int res = 0;
+
+	strbuf_getline(&line, stdin);
+
+	if (!line.len)
+		return 1;
+
+	/* Parse out the first two tokens, command and version. */
+	string_list_split_in_place(&tokens, line.buf, " ", 2);
+
+	if (tokens.nr < 2) {
+		res = error(_("expected at least 2 tokens, got %"PRIu32),
+			    (uint32_t)tokens.nr);
+		goto cleanup;
+	}
+
+	command = tokens.items[0].string;
+
+	if (!git_parse_int(tokens.items[1].string, &version)) {
+		res = error(_("unable to parse '%s' to integer"),
+			    tokens.items[1].string);
+		goto cleanup;
+	}
+
+	if (tokens.nr >= 3) {
+		data = tokens.items[2].string;
+		data_len = strlen(tokens.items[2].string);
+	}
+
+	for (size_t i = 0; i < COMMAND_COUNT; i++) {
+		/*
+		 * Run the ith command if we have hit the unknown
+		 * command or if the name and version match.
+		 */
+		if (!commands[i].name[0] ||
+		    (!strcmp(command, commands[i].name) &&
+		     commands[i].version == version)) {
+			res = commands[i].fn(repo, data, data_len);
+			goto cleanup;
+		}
+	}
+
+	BUG(_("scanned to end of command list, including 'unknown_command'"));
+
+cleanup:
+	strbuf_reset(&line);
+	string_list_clear(&tokens, 0);
+	return res;
+}
+
 int cmd_config_batch(int argc,
 		     const char **argv,
 		     const char *prefix,
 		     struct repository *repo)
 {
+	int res = 0;
 	struct option options[] = {
 		OPT_END(),
 	};
@@ -26,5 +153,9 @@ int cmd_config_batch(int argc,
 
 	repo_config(repo, git_default_config, NULL);
 
-	return 0;
+	while (!(res = process_command(repo)));
+
+	if (res == 1)
+		return 0;
+	die(_("an unrecoverable error occurred during command execution"));
 }
diff --git a/t/t1312-config-batch.sh b/t/t1312-config-batch.sh
index f59ba4a0f3..f60ef35e38 100755
--- a/t/t1312-config-batch.sh
+++ b/t/t1312-config-batch.sh
@@ -4,9 +4,22 @@ test_description='Test git config-batch'
 
 . ./test-lib.sh
 
-test_expect_success 'help text' '
-	test_must_fail git config-batch -h >out &&
-	grep usage out
+test_expect_success 'no commands' '
+	echo | git config-batch >out &&
+	test_must_be_empty out
+'
+
+test_expect_success 'unknown_command' '
+	echo unknown_command >expect &&
+	echo "bogus 1 line of tokens" >in &&
+	git config-batch >out <in &&
+	test_cmp expect out
+'
+
+test_expect_success 'failed to parse version' '
+	echo "bogus BAD_VERSION line of tokens" >in &&
+	test_must_fail git config-batch 2>err <in &&
+	test_grep BAD_VERSION err
 '
 
 test_done

Documentation/git-config-batch.adoc, builtin/config-batch.c, config.h, t/t1312-config-batch.sh

diff --git a/Documentation/git-config-batch.adoc b/Documentation/git-config-batch.adoc
index 9ca04b0c1e..31dd42f481 100644
--- a/Documentation/git-config-batch.adoc
+++ b/Documentation/git-config-batch.adoc
@@ -32,9 +32,58 @@ set. Thus, if the Git version includes the `git config-batch` builtin
 but doesn't understand an input command, it will return a single line
 response:
 
-```
+------------
 unknown_command LF
-```
+------------
+
+These are the commands that are currently understood:
+
+`get` version 1::
+	The `get` command searches the config key-value pairs within a
+	given `<scope>` for values that match the fixed `<key>` and
+	filters the resulting value based on an optional `<value-filter>`.
+	This can either be a regex or a fixed value. The command format
+	is one of the following formats:
++
+------------
+get 1 <scope> <key>
+get 1 <scope> <key> arg:regex <value-pattern>
+get 1 <scope> <key> arg:fixed-value <value>
+------------
++
+The `<scope>` value can be one of `inherited`, `system`, `global`,
+`local`, `worktree`, `submodule`, or `command`. If `inherited`, then all
+config key-value pairs will be considered regardless of scope. Otherwise,
+only the given scope will be considered.
++
+If no optional arguments are given, then the value will not be filtered
+by any pattern matching. If `arg:regex` is specified, then the rest of
+the line is considered a single string, `<value-pattern>`, and is
+interpreted as a regular expression for matching against stored values,
+similar to specifying a value to `get config --get <key> "<value-pattern>"`.
+If `arg:fixed-value` is specified, then the rest of the line is
+considered a single string, `<value>`, and is checked for an exact
+match against the key-value pairs, simmilar to `git config --get <key>
+--fixed-value "<value>"`.
++
+At mmost one key-value pair is returned, that being the last key-value
+pair in the standard config order by scope and sequence within each scope.
++
+If a key-value pair is found, then the following output is given:
++
+------------
+get 1 found <key> <scope> <value>
+------------
++
+If no matching key-value pair is found, then the following output is
+given:
++
+------------
+get 1 missing <key> [<value-pattern>|<value>]
+------------
++
+where `<value-pattern>` or `<value>` is only supplied if provided in
+the command.
 
 SEE ALSO
 --------
diff --git a/builtin/config-batch.c b/builtin/config-batch.c
index dffedb8ca2..5782004080 100644
--- a/builtin/config-batch.c
+++ b/builtin/config-batch.c
@@ -12,6 +12,8 @@ static const char *const builtin_config_batch_usage[] = {
 };
 
 #define UNKNOWN_COMMAND "unknown_command"
+#define GET_COMMAND "get"
+#define COMMAND_PARSE_ERROR "command_parse_error"
 
 static int emit_response(const char *response, ...)
 {
@@ -30,6 +32,11 @@ static int emit_response(const char *response, ...)
 	return 0;
 }
 
+static int command_parse_error(const char *command)
+{
+	return emit_response(COMMAND_PARSE_ERROR, command, NULL);
+}
+
 /**
  * A function pointer type for defining a command. The function is
  * responsible for handling different versions of the command name.
@@ -46,11 +53,248 @@ typedef int (*command_fn)(struct repository *repo,
 			  char *data, size_t data_len);
 
 static int unknown_command(struct repository *repo UNUSED,
-			  char *data UNUSED, size_t data_len UNUSED)
+			   char *data UNUSED, size_t data_len UNUSED)
 {
 	return emit_response(UNKNOWN_COMMAND, NULL);
 }
 
+static size_t parse_whitespace_token(char **data, size_t *data_len,
+				     char **token, int *err UNUSED)
+{
+	size_t i = 0;
+
+	*token = *data;
+
+	while (i < *data_len && (*data)[i] && (*data)[i] != ' ')
+		i++;
+
+	if (i >= *data_len) {
+		*data_len = 0;
+		*data = NULL;
+		return i;
+	}
+
+	(*data)[i] = 0;
+	*data_len = (*data_len) - (i + 1);
+	*data = *data + (i + 1);
+	return i;
+}
+
+/**
+ * Given the remaining data line and its size, attempt to extract
+ * a token. When the token delimiter is determined, the data
+ * string is mutated to insert a NUL byte at the end of the token.
+ * The data pointer is mutated to point at the next character (or
+ * set to NULL if that exceeds the string length). The data_len
+ * value is mutated to subtract the length of the discovered
+ * token.
+ *
+ * The returned value is the length of the token that was
+ * discovered.
+ *
+ * 'err' is ignored for now, but will be filled in in a future
+ * change.
+ */
+static size_t parse_token(char **data, size_t *data_len,
+			  char **token, int *err)
+{
+	if (!*data_len)
+		return 0;
+
+	return parse_whitespace_token(data, data_len, token, err);
+}
+
+enum value_match_mode {
+	MATCH_ALL,
+	MATCH_EXACT,
+	MATCH_REGEX,
+};
+
+struct get_command_1_data {
+	/* parameters */
+	char *key;
+	enum config_scope scope;
+	enum value_match_mode mode;
+
+	/* optional parameters */
+	char *value;
+	regex_t *value_pattern;
+
+	/* data along the way, for single values. */
+	char *found;
+	enum config_scope found_scope;
+};
+
+static int get_command_1_cb(const char *key, const char *value,
+			    const struct config_context *context,
+			    void *data)
+{
+	struct get_command_1_data *d = data;
+
+	if (strcasecmp(key, d->key))
+		return 0;
+
+	if (d->scope != CONFIG_SCOPE_UNKNOWN &&
+	    d->scope != context->kvi->scope)
+		return 0;
+
+	switch (d->mode) {
+	case MATCH_EXACT:
+		if (strcasecmp(value, d->value))
+			return 0;
+		break;
+
+	case MATCH_REGEX:
+		if (regexec(d->value_pattern, value, 0, NULL, 0))
+			return 0;
+		break;
+
+	default:
+		break;
+	}
+
+	free(d->found);
+	d->found = xstrdup(value);
+	d->found_scope = context->kvi->scope;
+	return 0;
+}
+
+static const char *scope_str(enum config_scope scope)
+{
+	switch (scope) {
+	case CONFIG_SCOPE_UNKNOWN:
+		return "unknown";
+
+	case CONFIG_SCOPE_SYSTEM:
+		return "system";
+
+	case CONFIG_SCOPE_GLOBAL:
+		return "global";
+
+	case CONFIG_SCOPE_LOCAL:
+		return "local";
+
+	case CONFIG_SCOPE_WORKTREE:
+		return "worktree";
+
+	case CONFIG_SCOPE_SUBMODULE:
+		return "submodule";
+
+	case CONFIG_SCOPE_COMMAND:
+		return "command";
+
+	default:
+		BUG("invalid config scope");
+	}
+}
+
+static int parse_scope(const char *str, enum config_scope *scope)
+{
+	if (!strcmp(str, "inherited")) {
+		*scope = CONFIG_SCOPE_UNKNOWN;
+		return 0;
+	}
+
+	for (enum config_scope s = 0; s < CONFIG_SCOPE__NR; s++) {
+		if (!strcmp(str, scope_str(s))) {
+			*scope = s;
+			return 0;
+		}
+	}
+
+	return -1;
+}
+
+/**
+ * 'get' command, version 1.
+ *
+ * Positional arguments should be of the form:
+ *
+ * [0] scope ("system", "global", "local", "worktree", "command", "submodule", or "inherited")
+ * [1] config key
+ * [2*] multi-mode ("regex", "fixed-value")
+ * [3*] value regex OR value string
+ *
+ * [N*] indicates optional parameters that are not needed.
+ */
+static int get_command_1(struct repository *repo,
+			 char *data,
+			 size_t data_len)
+{
+	struct get_command_1_data gc_data = {
+		.found = NULL,
+		.mode = MATCH_ALL,
+	};
+	int res = 0, err = 0;
+	char *token;
+	size_t token_len;
+
+	if (!parse_token(&data, &data_len, &token, &err) || err)
+		goto parse_error;
+
+	if (parse_scope(token, &gc_data.scope))
+		goto parse_error;
+
+	if (!parse_token(&data, &data_len, &gc_data.key, &err) || err)
+		goto parse_error;
+
+	token_len = parse_token(&data, &data_len, &token, &err);
+	if (err)
+		goto parse_error;
+
+	if (token_len && !strncmp(token, "arg:", 4)) {
+		if (!strcmp(token + 4, "regex"))
+			gc_data.mode = MATCH_REGEX;
+		else if (!strcmp(token + 4, "fixed-value"))
+			gc_data.mode = MATCH_EXACT;
+		else
+			goto parse_error; /* unknown arg. */
+
+		/* Use the remaining data as the value string. */
+		gc_data.value = data;
+
+		if (gc_data.mode == MATCH_REGEX) {
+			CALLOC_ARRAY(gc_data.value_pattern, 1);
+			if (regcomp(gc_data.value_pattern, gc_data.value,
+				    REG_EXTENDED)) {
+				FREE_AND_NULL(gc_data.value_pattern);
+				goto parse_error;
+			}
+		}
+	} else if (token_len) {
+		/*
+		 * If we have remaining tokens not starting in "arg:",
+		 * then we don't understand them.
+		 */
+		goto parse_error;
+	}
+
+	repo_config(repo, get_command_1_cb, &gc_data);
+
+	if (gc_data.found)
+		res = emit_response(GET_COMMAND, "1", "found", gc_data.key,
+				    scope_str(gc_data.found_scope),
+				    gc_data.found,
+				    NULL);
+	else
+		res = emit_response(GET_COMMAND, "1", "missing", gc_data.key,
+				    gc_data.value, NULL);
+
+	goto cleanup;
+
+
+parse_error:
+	res = command_parse_error(GET_COMMAND);
+
+cleanup:
+	if (gc_data.value_pattern) {
+		regfree(gc_data.value_pattern);
+		free(gc_data.value_pattern);
+	}
+	free(gc_data.found);
+	return res;
+}
+
 struct command {
 	const char *name;
 	command_fn fn;
@@ -58,6 +302,11 @@ struct command {
 };
 
 static struct command commands[] = {
+	{
+		.name = GET_COMMAND,
+		.fn = get_command_1,
+		.version = 1,
+	},
 	/* unknown_command must be last. */
 	{
 		.name = "",
diff --git a/config.h b/config.h
index ba426a960a..966a228f0e 100644
--- a/config.h
+++ b/config.h
@@ -44,6 +44,9 @@ enum config_scope {
 	CONFIG_SCOPE_WORKTREE,
 	CONFIG_SCOPE_COMMAND,
 	CONFIG_SCOPE_SUBMODULE,
+
+	/* Must be last */
+	CONFIG_SCOPE__NR
 };
 const char *config_scope_name(enum config_scope scope);
 
diff --git a/t/t1312-config-batch.sh b/t/t1312-config-batch.sh
index f60ef35e38..e638b54d13 100755
--- a/t/t1312-config-batch.sh
+++ b/t/t1312-config-batch.sh
@@ -16,10 +16,111 @@ test_expect_success 'unknown_command' '
 	test_cmp expect out
 '
 
+test_expect_success 'completely broken input' '
+	echo "not_even_two_tokens" >in &&
+	test_must_fail git config-batch 2>err <in &&
+	test_grep "expected at least 2 tokens" err &&
+	test_grep "an unrecoverable error occurred during command execution" err
+'
+
 test_expect_success 'failed to parse version' '
 	echo "bogus BAD_VERSION line of tokens" >in &&
 	test_must_fail git config-batch 2>err <in &&
 	test_grep BAD_VERSION err
 '
 
+test_expect_success 'get inherited config' '
+	test_when_finished git config --unset test.key &&
+
+	git config test.key "test value with spaces" &&
+
+	echo "get 1 inherited test.key" >in &&
+	echo "get 1 found test.key local test value with spaces" >expect &&
+	git config-batch >out <in &&
+	test_cmp expect out &&
+
+	echo "get 1 global test.key" >in &&
+	echo "get 1 missing test.key" >expect &&
+	git config-batch >out <in &&
+	test_cmp expect out
+'
+
+test_expect_success 'set up worktree' '
+	test_commit A &&
+	git config extensions.worktreeconfig true &&
+	git worktree add --detach worktree
+'
+
+test_expect_success 'get config with arg:regex' '
+	test_when_finished git config --unset-all test.key &&
+	GIT_CONFIG_SYSTEM=system-config-file &&
+	GIT_CONFIG_NOSYSTEM=0 &&
+	GIT_CONFIG_GLOBAL=global-config-file &&
+	export GIT_CONFIG_SYSTEM &&
+	export GIT_CONFIG_NOSYSTEM &&
+	export GIT_CONFIG_GLOBAL &&
+
+	git config --system test.key on1e &&
+	git config --global test.key t2wo &&
+	git config test.key "thre3e space" &&
+	git config --worktree test.key 4four &&
+
+	cat >in <<-\EOF &&
+	get 1 inherited test.key arg:regex .*1.*
+	get 1 inherited test.key arg:regex [a-z]2.*
+	get 1 inherited test.key arg:regex .*3e s.*
+	get 1 inherited test.key arg:regex 4.*
+	get 1 inherited test.key arg:regex .*5.*
+	get 1 inherited test.key arg:regex .*6.*
+	EOF
+
+	cat >expect <<-\EOF &&
+	get 1 found test.key system on1e
+	get 1 found test.key global t2wo
+	get 1 found test.key local thre3e space
+	get 1 found test.key worktree 4four
+	get 1 found test.key command five5
+	get 1 missing test.key .*6.*
+	EOF
+
+	git -c test.key=five5 config-batch >out <in &&
+	test_cmp expect out
+'
+
+test_expect_success 'get config with arg:fixed-value' '
+	test_when_finished git config --unset-all test.key &&
+	GIT_CONFIG_SYSTEM=system-config-file &&
+	GIT_CONFIG_NOSYSTEM=0 &&
+	GIT_CONFIG_GLOBAL=global-config-file &&
+	export GIT_CONFIG_SYSTEM &&
+	export GIT_CONFIG_NOSYSTEM &&
+	export GIT_CONFIG_GLOBAL &&
+
+	git config --system test.key one &&
+	git config --global test.key two &&
+	git config test.key "three space" &&
+	git config --worktree test.key four &&
+
+	cat >in <<-\EOF &&
+	get 1 inherited test.key arg:fixed-value one
+	get 1 inherited test.key arg:fixed-value two
+	get 1 inherited test.key arg:fixed-value three space
+	get 1 inherited test.key arg:fixed-value four
+	get 1 inherited test.key arg:fixed-value five
+	get 1 inherited test.key arg:fixed-value six
+	EOF
+
+	cat >expect <<-\EOF &&
+	get 1 found test.key system one
+	get 1 found test.key global two
+	get 1 found test.key local three space
+	get 1 found test.key worktree four
+	get 1 found test.key command five
+	get 1 missing test.key six
+	EOF
+
+	git -c test.key=five config-batch >out <in &&
+	test_cmp expect out
+'
+
 test_done

Documentation/git-config-batch.adoc, builtin/config-batch.c, t/t1312-config-batch.sh

diff --git a/Documentation/git-config-batch.adoc b/Documentation/git-config-batch.adoc
index 31dd42f481..1fff68a13c 100644
--- a/Documentation/git-config-batch.adoc
+++ b/Documentation/git-config-batch.adoc
@@ -38,6 +38,23 @@ unknown_command LF
 
 These are the commands that are currently understood:
 
+`help` version 1::
+	The `help` command lists the currently-available commands in
+	this version of Git. The output is multi-line, but the first
+	line provides the count of possible commands via `help count <N>`.
+	The next `<N>` lines are of the form `help <command> <version>`
+	to state that this Git version supports that `<command>` at
+	version `<version>`. Note that the same command may have multiple
+	available versions.
++
+Here is the currentl output of the help text at the latest version:
++
+------------
+help 1 count 2
+help 1 help 1
+help 1 get 1
+------------
+
 `get` version 1::
 	The `get` command searches the config key-value pairs within a
 	given `<scope>` for values that match the fixed `<key>` and
diff --git a/builtin/config-batch.c b/builtin/config-batch.c
index 5782004080..1c19e4889f 100644
--- a/builtin/config-batch.c
+++ b/builtin/config-batch.c
@@ -12,6 +12,7 @@ static const char *const builtin_config_batch_usage[] = {
 };
 
 #define UNKNOWN_COMMAND "unknown_command"
+#define HELP_COMMAND "help"
 #define GET_COMMAND "get"
 #define COMMAND_PARSE_ERROR "command_parse_error"
 
@@ -104,6 +105,9 @@ static size_t parse_token(char **data, size_t *data_len,
 	return parse_whitespace_token(data, data_len, token, err);
 }
 
+static int help_command_1(struct repository *repo,
+			  char *data, size_t data_len);
+
 enum value_match_mode {
 	MATCH_ALL,
 	MATCH_EXACT,
@@ -302,6 +306,11 @@ struct command {
 };
 
 static struct command commands[] = {
+	{
+		.name = HELP_COMMAND,
+		.fn = help_command_1,
+		.version = 1,
+	},
 	{
 		.name = GET_COMMAND,
 		.fn = get_command_1,
@@ -316,6 +325,29 @@ static struct command commands[] = {
 
 #define COMMAND_COUNT ((size_t)(sizeof(commands) / sizeof(*commands)))
 
+static int help_command_1(struct repository *repo UNUSED,
+			  char *data UNUSED, size_t data_len UNUSED)
+{
+	struct strbuf fmt_str = STRBUF_INIT;
+
+	strbuf_addf(&fmt_str, "%"PRIu32, (uint32_t)(COMMAND_COUNT - 1));
+	emit_response(HELP_COMMAND, "1", "count", fmt_str.buf, NULL);
+	strbuf_reset(&fmt_str);
+
+	for (size_t i = 0; i < COMMAND_COUNT; i++) {
+		/* Halt at unknown command. */
+		if (!commands[i].name[0])
+			break;
+
+		strbuf_addf(&fmt_str, "%d", commands[i].version);
+		emit_response(HELP_COMMAND, "1", commands[i].name, fmt_str.buf, NULL);
+		strbuf_reset(&fmt_str);
+	}
+
+	strbuf_release(&fmt_str);
+	return 0;
+}
+
 /**
  * Process a single line from stdin and process the command.
  *
diff --git a/t/t1312-config-batch.sh b/t/t1312-config-batch.sh
index e638b54d13..6b550a0e76 100755
--- a/t/t1312-config-batch.sh
+++ b/t/t1312-config-batch.sh
@@ -23,6 +23,19 @@ test_expect_success 'completely broken input' '
 	test_grep "an unrecoverable error occurred during command execution" err
 '
 
+test_expect_success 'help command' '
+	echo "help 1" >in &&
+
+	cat >expect <<-\EOF &&
+	help 1 count 2
+	help 1 help 1
+	help 1 get 1
+	EOF
+
+	git config-batch >out <in &&
+	test_cmp expect out
+'
+
 test_expect_success 'failed to parse version' '
 	echo "bogus BAD_VERSION line of tokens" >in &&
 	test_must_fail git config-batch 2>err <in &&

Documentation/git-config-batch.adoc, builtin/config-batch.c, t/t1312-config-batch.sh

diff --git a/Documentation/git-config-batch.adoc b/Documentation/git-config-batch.adoc
index 1fff68a13c..3c9a3bb763 100644
--- a/Documentation/git-config-batch.adoc
+++ b/Documentation/git-config-batch.adoc
@@ -21,6 +21,15 @@ multiple configuration values, the `git config-batch` command allows a
 single process to handle multiple requests using a machine-parseable
 interface across `stdin` and `stdout`.
 
+OPTIONS
+-------
+
+`-z`::
+	If specified, then use the NUL-terminated input and output
+	format instead of the space and newline format. This format is
+	useful when the strings involved may include spaces or newlines.
+	See PROTOCOL for more details.
+
 PROTOCOL
 --------
 By default, the protocol uses line feeds (`LF`) to signal the end of a
@@ -41,13 +50,13 @@ These are the commands that are currently understood:
 `help` version 1::
 	The `help` command lists the currently-available commands in
 	this version of Git. The output is multi-line, but the first
-	line provides the count of possible commands via `help count <N>`.
-	The next `<N>` lines are of the form `help <command> <version>`
+	line provides the count of possible commands via `help 1 count <N>`.
+	The next `<N>` lines are of the form `help 1 <command> <version>`
 	to state that this Git version supports that `<command>` at
 	version `<version>`. Note that the same command may have multiple
 	available versions.
 +
-Here is the currentl output of the help text at the latest version:
+Here is the current output of the help text at the latest version:
 +
 ------------
 help 1 count 2
@@ -102,6 +111,48 @@ get 1 missing <key> [<value-pattern>|<value>]
 where `<value-pattern>` or `<value>` is only supplied if provided in
 the command.
 
+NUL-Terminated Format
+~~~~~~~~~~~~~~~~~~~~~
+
+When `-z` is given, the protocol changes in some structural ways.
+
+First, each command is terminated with two NUL bytes, providing a clear
+boundary between commands regardless of future possibilities of new
+command formats.
+
+Second, any time that a space _would_ be used to partition tokens in a
+command, a NUL byte is used instead. Further, each token is prefixed
+with `<N>:` where `<N>` is a decimal representation of the length of
+the string between the `:` and the next NUL byte. Any disagreement in
+these lengths is treated as a parsing error. This use of a length does
+imply that "`0:`" is the representation of an empty string, if relevant.
+
+The decimal representation must have at most five numerals, thus the
+maximum length of a string token can have 99999 characters.
+
+For example, the `get` command, version 1, could have any of the
+following forms:
+
+------------
+3:get NUL 1:1 NUL 5:local NUL 14:key.with space NUL NUL
+3:get NUL 1:1 NUL 9:inherit NUL 8:test.key NUL 9:arg:regex NUL 6:.*\ .* NUL NUL
+3:get NUL 1:1 NUL 6:global NUL 8:test.key NUL 15:arg:fixed-value NUL 3:a b NUL NUL
+------------
+
+The output is modified similarly, such as the following output examples,
+as if the input has a parse error, a valid `help` command, a `get`
+command that had a match, and a `get` command that did not match.
+
+------------
+15:unknown_command NUL NUL
+4:help NUL 1:1 NUL 5:count NUL 1:2 NUL NUL
+4:help NUL 1:1 NUL 4:help NUL 1:1 NUL NUL
+4:help NUL 1:1 NUL 3:get NUL 1:1 NUL NUL
+3:get NUL 1:1 NUL 5:found NUL 8:test.key NUL 5:value NUL NUL
+3:get NUL 1:1 NUL 7:missing NUL 8:test.key NUL NUL
+------------
+
+
 SEE ALSO
 --------
 linkgit:git-config[1]
diff --git a/builtin/config-batch.c b/builtin/config-batch.c
index 1c19e4889f..2c48c4ea37 100644
--- a/builtin/config-batch.c
+++ b/builtin/config-batch.c
@@ -11,24 +11,40 @@ static const char *const builtin_config_batch_usage[] = {
 	NULL
 };
 
+static int zformat = 0;
+
 #define UNKNOWN_COMMAND "unknown_command"
 #define HELP_COMMAND "help"
 #define GET_COMMAND "get"
 #define COMMAND_PARSE_ERROR "command_parse_error"
 
+static void print_word(const char *word, int start)
+{
+	if (zformat) {
+		printf("%"PRIu32":%s", (uint32_t)strlen(word), word);
+		fputc(0, stdout);
+	} else if (start)
+		printf("%s", word);
+	else
+		printf(" %s", word);
+}
+
 static int emit_response(const char *response, ...)
 {
 	va_list params;
 	const char *token;
 
-	printf("%s", response);
+	print_word(response, 1);
 
 	va_start(params, response);
 	while ((token = va_arg(params, const char *)))
-		printf(" %s", token);
+		print_word(token, 0);
 	va_end(params);
 
-	printf("\n");
+	if (zformat)
+		fputc(0, stdout);
+	else
+		printf("\n");
 	fflush(stdout);
 	return 0;
 }
@@ -59,6 +75,52 @@ static int unknown_command(struct repository *repo UNUSED,
 	return emit_response(UNKNOWN_COMMAND, NULL);
 }
 
+/*
+ * Parse the next token using the NUL-byte format.
+ */
+static size_t parse_ztoken(char **data, size_t *data_len,
+			   char **token, int *err)
+{
+	size_t i = 0, token_len;
+
+	while (i < *data_len && (*data)[i] != ':') {
+		if ((*data)[i] < '0' || (*data)[i] > '9') {
+			goto parse_error;
+		}
+		i++;
+	}
+
+	if (i >= *data_len || (*data)[i] != ':' || i > 5)
+		goto parse_error;
+
+	(*data)[i] = 0;
+	token_len = atoi(*data);
+
+	if (token_len + i + 1 >= *data_len)
+		goto parse_error;
+
+	*token = *data + i + 1;
+	*data_len = *data_len - (i + 1);
+
+	/* check for early NULs. */
+	for (i = 0; i < token_len; i++) {
+		if (!(*token)[i])
+			goto parse_error;
+	}
+	/* check for matching NUL. */
+	if ((*token)[token_len])
+		goto parse_error;
+
+	*data = *token + token_len + 1;
+	*data_len = *data_len - (token_len + 1);
+	return token_len;
+
+parse_error:
+	*err = 1;
+	*token = NULL;
+	return 0;
+}
+
 static size_t parse_whitespace_token(char **data, size_t *data_len,
 				     char **token, int *err UNUSED)
 {
@@ -93,15 +155,23 @@ static size_t parse_whitespace_token(char **data, size_t *data_len,
  * The returned value is the length of the token that was
  * discovered.
  *
- * 'err' is ignored for now, but will be filled in in a future
- * change.
+ * The 'token' pointer is used to set the start of the token.
+ * In the whitespace format, this is always the input value of
+ * 'data' but in the NUL-terminated format this follows an "<N>:"
+ * prefix.
+ *
+ * In the case of the NUL-terminated format, a bad parse of the
+ * decimal length or a mismatch of the decimal length and the
+ * length of the following NUL-terminated string will result in
+ * the value pointed at by 'err' to be set to 1.
  */
 static size_t parse_token(char **data, size_t *data_len,
 			  char **token, int *err)
 {
 	if (!*data_len)
 		return 0;
-
+	if (zformat)
+		return parse_ztoken(data, data_len, token, err);
 	return parse_whitespace_token(data, data_len, token, err);
 }
 
@@ -255,7 +325,13 @@ static int get_command_1(struct repository *repo,
 			goto parse_error; /* unknown arg. */
 
 		/* Use the remaining data as the value string. */
-		gc_data.value = data;
+		if (!zformat)
+			gc_data.value = data;
+		else {
+			parse_token(&data, &data_len, &gc_data.value, &err);
+			if (err)
+				goto parse_error;
+		}
 
 		if (gc_data.mode == MATCH_REGEX) {
 			CALLOC_ARRAY(gc_data.value_pattern, 1);
@@ -348,17 +424,74 @@ static int help_command_1(struct repository *repo UNUSED,
 	return 0;
 }
 
-/**
- * Process a single line from stdin and process the command.
- *
- * Returns 0 on successful processing of command, including the
- * unknown_command output.
- *
- * Returns 1 on natural exit due to exist signal of empty line.
- *
- * Returns negative value on other catastrophic error.
- */
-static int process_command(struct repository *repo)
+static int process_command_nul(struct repository *repo)
+{
+	static struct strbuf line = STRBUF_INIT;
+	char *data, *command, *versionstr;
+	size_t data_len, token_len;
+	int res = 0, err = 0, version = 0, getc;
+	char c;
+
+	/* If we start with EOF it's not an error. */
+	getc = fgetc(stdin);
+	if (getc == EOF)
+		return 1;
+
+	do {
+		c = (char)getc;
+		strbuf_addch(&line, c);
+
+		if (!c && line.len > 1 && !line.buf[line.len - 2])
+			break;
+
+		getc = fgetc(stdin);
+
+		/* It's an error if we reach EOF while parsing a command. */
+		if (getc == EOF)
+			goto parse_error;
+	} while (1);
+
+	data = line.buf;
+	data_len = line.len - 1;
+
+	token_len = parse_ztoken(&data, &data_len, &command, &err);
+	if (!token_len || err)
+		goto parse_error;
+
+	token_len = parse_ztoken(&data, &data_len, &versionstr, &err);
+	if (!token_len || err)
+		goto parse_error;
+
+	if (!git_parse_int(versionstr, &version)) {
+		res = error(_("unable to parse '%s' to integer"),
+			    versionstr);
+		goto parse_error;
+	}
+
+	for (size_t i = 0; i < COMMAND_COUNT; i++) {
+		/*
+		 * Run the ith command if we have hit the unknown
+		 * command or if the name and version match.
+		 */
+		if (!commands[i].name[0] ||
+		    (!strcmp(command, commands[i].name) &&
+		     commands[i].version == version)) {
+			res = commands[i].fn(repo, data, data_len);
+			goto cleanup;
+		}
+	}
+
+	BUG(_("scanned to end of command list, including 'unknown_command'"));
+
+parse_error:
+	res = unknown_command(repo, NULL, 0);
+
+cleanup:
+	strbuf_release(&line);
+	return res;
+}
+
+static int process_command_whitespace(struct repository *repo)
 {
 	static struct strbuf line = STRBUF_INIT;
 	struct string_list tokens = STRING_LIST_INIT_NODUP;
@@ -416,6 +549,23 @@ cleanup:
 	return res;
 }
 
+/**
+ * Process a single line from stdin and process the command.
+ *
+ * Returns 0 on successful processing of command, including the
+ * unknown_command output.
+ *
+ * Returns 1 on natural exit due to exist signal of empty line.
+ *
+ * Returns negative value on other catastrophic error.
+ */
+static int process_command(struct repository *repo)
+{
+	if (zformat)
+		return process_command_nul(repo);
+	return process_command_whitespace(repo);
+}
+
 int cmd_config_batch(int argc,
 		     const char **argv,
 		     const char *prefix,
@@ -423,6 +573,8 @@ int cmd_config_batch(int argc,
 {
 	int res = 0;
 	struct option options[] = {
+		OPT_BOOL('z', NULL, &zformat,
+			 N_("stdin and stdout is NUL-terminated")),
 		OPT_END(),
 	};
 
diff --git a/t/t1312-config-batch.sh b/t/t1312-config-batch.sh
index 6b550a0e76..f7a74ddc2c 100755
--- a/t/t1312-config-batch.sh
+++ b/t/t1312-config-batch.sh
@@ -4,6 +4,26 @@ test_description='Test git config-batch'
 
 . ./test-lib.sh
 
+# usage: test_zformat <command> <args> <in >out
+#
+# Let 'in' be a z-format input but with " NUL " between tokens in
+# a single command and " NUL NUL" trailing each line.
+#
+# The values in 'out' will be space- and newline-delimited where
+# NUL-bytes would normally be output.
+test_zformat () {
+	sed -e "s/\ NUL\ /!/g" >nullin1 &&
+	sed -e "s/NUL//g" <nullin1 >nullin2 &&
+
+	tr "!" "\0" <nullin2 >nullin3 &&
+	tr "\n" "\0" <nullin3 >zin &&
+
+	$* <zin >zout &&
+
+	tr "\0" " " <zout >outspace &&
+	sed "s/\ \ /\n/g" <outspace
+}
+
 test_expect_success 'no commands' '
 	echo | git config-batch >out &&
 	test_must_be_empty out
@@ -36,6 +56,23 @@ test_expect_success 'help command' '
 	test_cmp expect out
 '
 
+test_expect_success 'help -z' '
+	cat >in <<-\EOF &&
+	4:help NUL 1:1 NUL NUL
+	5:bogus NUL 2:10 NUL NUL
+	EOF
+
+	cat >expect <<-\EOF &&
+	4:help 1:1 5:count 1:2
+	4:help 1:1 4:help 1:1
+	4:help 1:1 3:get 1:1
+	15:unknown_command
+	EOF
+
+	test_zformat git config-batch -z >out <in &&
+	test_cmp expect out
+'
+
 test_expect_success 'failed to parse version' '
 	echo "bogus BAD_VERSION line of tokens" >in &&
 	test_must_fail git config-batch 2>err <in &&
@@ -136,4 +173,36 @@ test_expect_success 'get config with arg:fixed-value' '
 	test_cmp expect out
 '
 
+test_expect_success 'get config with -z' '
+	test_when_finished git config --unset-all test.key &&
+	GIT_CONFIG_SYSTEM=system-config-file &&
+	GIT_CONFIG_NOSYSTEM=0 &&
+	GIT_CONFIG_GLOBAL=global-config-file &&
+	export GIT_CONFIG_SYSTEM &&
+	export GIT_CONFIG_NOSYSTEM &&
+	export GIT_CONFIG_GLOBAL &&
+
+	git config --system test.key on1e &&
+	git config --global test.key t2wo &&
+	git config test.key "thre3e space" &&
+	git config --worktree test.key 4four &&
+
+	cat >in <<-\EOF &&
+	3:get NUL 1:1 NUL 9:inherited NUL 8:test.key NUL NUL
+	3:get NUL 1:1 NUL 6:global NUL 8:test.key NUL 9:arg:regex NUL 3:2.* NUL NUL
+	3:get NUL 1:1 NUL 5:local NUL 8:test.key NUL 15:arg:fixed-value NUL 12:thre3e space NUL NUL
+	3:get NUL 1:1 NUL 9:inherited NUL 11:key.missing NUL NUL
+	EOF
+
+	cat >expect <<-\EOF &&
+	3:get 1:1 5:found 8:test.key 8:worktree 5:4four
+	3:get 1:1 5:found 8:test.key 6:global 4:t2wo
+	3:get 1:1 5:found 8:test.key 5:local 12:thre3e space
+	3:get 1:1 7:missing 11:key.missing
+	EOF
+
+	test_zformat git config-batch -z >out <in &&
+	test_cmp expect out
+'
+
 test_done

diff --git a/Documentation/technical/config-batch.adoc b/Documentation/technical/config-batch.adoc
new file mode 100644
index 0000000000..dbd614ad4f
--- /dev/null
+++ b/Documentation/technical/config-batch.adoc
@@ -0,0 +1,70 @@
+Git Config-Batch Design Notes
+=============================
+
+The `git config-batch` builtin has a robust protocol for parsing multiple
+commands over `stdin` and providing structured output over `stdout`. The
+intended use is for scripts or third-party software to interact with the
+config settings of a repository multiple times within the same Git process.
+The protocol is built with versioning that allows the consumer to know when
+a certain command is available and to fall back to single-use `git config`
+processes if the installed Git version does not have the latest commands
+at the required versions.
+
+Recommended interaction pattern
+-------------------------------
+
+This section provides a guide for ideal interaction with the `git
+config-batch` command and its protocol.
+
+For maximum compatibility, do not attempt parsing the output of `git
+version` to determine which commands are available. Instead, first check
+if the `git config-batch` command succeeds and does not die immediately
+due to the builtin being unavailable. Then, use the v1 of the `help`
+command to get a list of available commands and versions. Use this list to
+determine if your capabilities are available or should be replaced with an
+appropriate `git config` single-use process.
+
+Further, all automated tooling would be better off using the
+NUL-terminated format instead of the whitespace-delimited format, in case
+config keys contain spaces or config values contain newlines. The
+whitespace-delimited version is available for simpler integration and
+human inspection.
+
+Current commands
+----------------
+
+See the documentation in linkgit::config-batch[1] for the latest set of
+available commands and their protocols.
+
+Future commands
+---------------
+
+The following modes of `git config` are not currently available as commands
+in `git config-batch`, but are planned for future integration:
+
+`git config list [--<scope>]`::
+	Getting all values, regardless of config key, would require a
+	multi-valued output similar to the `help` command. This tool will
+	likely assume advanced options such as `--show-origin`.
+
+`git config set [--<scope>] <key> <value>`::
+	It will be desirable to set a config key at a given scope as a
+	single value, replacing the current value at that scope, if it
+	exists and is a single value. A `set` command could satisfy this
+	purpose.
+
+`git config set --all [<value-pattern>|--fixed-value=<fixedvalue>] <key> <value>`::
+	When replacing multiple values, it may be necessary to have a different
+	output describing the places those values were set, so it may need to
+	be implemented via a `set-all` command to differentiate from a `set`
+	command.
+
+`git config unset <key>`::
+
+`git config unset --all [<value-pattern>|--fixed-value=<fixedvalue>] <key>`::
+
+`git config get --all --rexexp <key-pattern> [<value-options>]`::
+
+`--replace-all` option::
+
+`--type=<type>` option::

builtin/config.c, config.c, config.h

diff --git a/builtin/config.c b/builtin/config.c
index 288ebdfdaa..d129b1204d 100644
--- a/builtin/config.c
+++ b/builtin/config.c
@@ -71,20 +71,6 @@ static const char *const builtin_config_edit_usage[] = {
 	OPT_STRING('f', "file", &opts.source.file, N_("file"), N_("use given config file")), \
 	OPT_STRING(0, "blob", &opts.source.blob, N_("blob-id"), N_("read config from given blob object"))
 
-struct config_location_options {
-	struct git_config_source source;
-	struct config_options options;
-	char *file_to_free;
-	int use_global_config;
-	int use_system_config;
-	int use_local_config;
-	int use_worktree_config;
-	int respect_includes_opt;
-};
-#define CONFIG_LOCATION_OPTIONS_INIT { \
-	.respect_includes_opt = -1, \
-}
-
 #define CONFIG_TYPE_OPTIONS(type) \
 	OPT_GROUP(N_("Type")), \
 	OPT_CALLBACK('t', "type", &type, N_("type"), N_("value is given this type"), option_parse_type), \
@@ -772,93 +758,6 @@ static char *default_user_config(void)
 	return strbuf_detach(&buf, NULL);
 }
 
-static void location_options_init(struct config_location_options *opts,
-				  const char *prefix)
-{
-	if (!opts->source.file)
-		opts->source.file = opts->file_to_free =
-			xstrdup_or_null(getenv(CONFIG_ENVIRONMENT));
-
-	if (opts->use_global_config + opts->use_system_config +
-	    opts->use_local_config + opts->use_worktree_config +
-	    !!opts->source.file + !!opts->source.blob > 1) {
-		error(_("only one config file at a time"));
-		exit(129);
-	}
-
-	if (!startup_info->have_repository) {
-		if (opts->use_local_config)
-			die(_("--local can only be used inside a git repository"));
-		if (opts->source.blob)
-			die(_("--blob can only be used inside a git repository"));
-		if (opts->use_worktree_config)
-			die(_("--worktree can only be used inside a git repository"));
-	}
-
-	if (opts->source.file &&
-			!strcmp(opts->source.file, "-")) {
-		opts->source.file = NULL;
-		opts->source.use_stdin = 1;
-		opts->source.scope = CONFIG_SCOPE_COMMAND;
-	}
-
-	if (opts->use_global_config) {
-		opts->source.file = opts->file_to_free = git_global_config();
-		if (!opts->source.file)
-			/*
-			 * It is unknown if HOME/.gitconfig exists, so
-			 * we do not know if we should write to XDG
-			 * location; error out even if XDG_CONFIG_HOME
-			 * is set and points at a sane location.
-			 */
-			die(_("$HOME not set"));
-		opts->source.scope = CONFIG_SCOPE_GLOBAL;
-	} else if (opts->use_system_config) {
-		opts->source.file = opts->file_to_free = git_system_config();
-		opts->source.scope = CONFIG_SCOPE_SYSTEM;
-	} else if (opts->use_local_config) {
-		opts->source.file = opts->file_to_free = repo_git_path(the_repository, "config");
-		opts->source.scope = CONFIG_SCOPE_LOCAL;
-	} else if (opts->use_worktree_config) {
-		struct worktree **worktrees = get_worktrees();
-		if (the_repository->repository_format_worktree_config)
-			opts->source.file = opts->file_to_free =
-				repo_git_path(the_repository, "config.worktree");
-		else if (worktrees[0] && worktrees[1])
-			die(_("--worktree cannot be used with multiple "
-			      "working trees unless the config\n"
-			      "extension worktreeConfig is enabled. "
-			      "Please read \"CONFIGURATION FILE\"\n"
-			      "section in \"git help worktree\" for details"));
-		else
-			opts->source.file = opts->file_to_free =
-				repo_git_path(the_repository, "config");
-		opts->source.scope = CONFIG_SCOPE_LOCAL;
-		free_worktrees(worktrees);
-	} else if (opts->source.file) {
-		if (!is_absolute_path(opts->source.file) && prefix)
-			opts->source.file = opts->file_to_free =
-				prefix_filename(prefix, opts->source.file);
-		opts->source.scope = CONFIG_SCOPE_COMMAND;
-	} else if (opts->source.blob) {
-		opts->source.scope = CONFIG_SCOPE_COMMAND;
-	}
-
-	if (opts->respect_includes_opt == -1)
-		opts->options.respect_includes = !opts->source.file;
-	else
-		opts->options.respect_includes = opts->respect_includes_opt;
-	if (startup_info->have_repository) {
-		opts->options.commondir = repo_get_common_dir(the_repository);
-		opts->options.git_dir = repo_get_git_dir(the_repository);
-	}
-}
-
-static void location_options_release(struct config_location_options *opts)
-{
-	free(opts->file_to_free);
-}
-
 static void display_options_init(struct config_display_options *opts)
 {
 	if (opts->end_nul) {
@@ -885,7 +784,7 @@ static int cmd_config_list(int argc, const char **argv, const char *prefix,
 	argc = parse_options(argc, argv, prefix, opts, builtin_config_list_usage, 0);
 	check_argc(argc, 0, 0);
 
-	location_options_init(&location_opts, prefix);
+	location_options_init(the_repository, &location_opts, prefix);
 	display_options_init(&display_opts);
 
 	setup_auto_pager("config", 1);
@@ -944,7 +843,7 @@ static int cmd_config_get(int argc, const char **argv, const char *prefix,
 		    value_pattern))
 		die(_("--url= cannot be used with --all, --regexp or --value"));
 
-	location_options_init(&location_opts, prefix);
+	location_options_init(the_repository, &location_opts, prefix);
 	display_options_init(&display_opts);
 
 	if (display_opts.type != TYPE_COLOR)
@@ -998,7 +897,7 @@ static int cmd_config_set(int argc, const char **argv, const char *prefix,
 
 	comment = git_config_prepare_comment_string(comment_arg);
 
-	location_options_init(&location_opts, prefix);
+	location_options_init(the_repository, &location_opts, prefix);
 	check_write(&location_opts.source);
 
 	value = normalize_value(argv[0], argv[1], type, &default_kvi);
@@ -1044,7 +943,7 @@ static int cmd_config_unset(int argc, const char **argv, const char *prefix,
 	if ((flags & CONFIG_FLAGS_FIXED_VALUE) && !value_pattern)
 		die(_("--fixed-value only applies with 'value-pattern'"));
 
-	location_options_init(&location_opts, prefix);
+	location_options_init(the_repository, &location_opts, prefix);
 	check_write(&location_opts.source);
 
 	if ((flags & CONFIG_FLAGS_MULTI_REPLACE) || value_pattern)
@@ -1073,7 +972,7 @@ static int cmd_config_rename_section(int argc, const char **argv, const char *pr
 			     PARSE_OPT_STOP_AT_NON_OPTION);
 	check_argc(argc, 2, 2);
 
-	location_options_init(&location_opts, prefix);
+	location_options_init(the_repository, &location_opts, prefix);
 	check_write(&location_opts.source);
 
 	ret = repo_config_rename_section_in_file(the_repository, location_opts.source.file,
@@ -1103,7 +1002,7 @@ static int cmd_config_remove_section(int argc, const char **argv, const char *pr
 			     PARSE_OPT_STOP_AT_NON_OPTION);
 	check_argc(argc, 1, 1);
 
-	location_options_init(&location_opts, prefix);
+	location_options_init(the_repository, &location_opts, prefix);
 	check_write(&location_opts.source);
 
 	ret = repo_config_rename_section_in_file(the_repository, location_opts.source.file,
@@ -1163,7 +1062,7 @@ static int cmd_config_edit(int argc, const char **argv, const char *prefix,
 	argc = parse_options(argc, argv, prefix, opts, builtin_config_edit_usage, 0);
 	check_argc(argc, 0, 0);
 
-	location_options_init(&location_opts, prefix);
+	location_options_init(the_repository, &location_opts, prefix);
 	check_write(&location_opts.source);
 
 	ret = show_editor(&location_opts);
@@ -1231,7 +1130,7 @@ static int cmd_config_actions(int argc, const char **argv, const char *prefix)
 			     builtin_config_usage,
 			     PARSE_OPT_STOP_AT_NON_OPTION);
 
-	location_options_init(&location_opts, prefix);
+	location_options_init(the_repository, &location_opts, prefix);
 	display_options_init(&display_opts);
 
 	if ((actions & (ACTION_GET_COLOR|ACTION_GET_COLORBOOL)) && display_opts.type) {
diff --git a/config.c b/config.c
index 7f6d53b473..9f1a7b45cf 100644
--- a/config.c
+++ b/config.c
@@ -35,6 +35,7 @@
 #include "strvec.h"
 #include "trace2.h"
 #include "wildmatch.h"
+#include "worktree.h"
 #include "write-or-die.h"
 
 struct config_source {
@@ -3592,3 +3593,91 @@ int lookup_config(const char **mapping, int nr_mapping, const char *var)
 	}
 	return -1;
 }
+
+void location_options_init(struct repository *repo,
+			   struct config_location_options *opts,
+			   const char *prefix)
+{
+	if (!opts->source.file)
+		opts->source.file = opts->file_to_free =
+			xstrdup_or_null(getenv(CONFIG_ENVIRONMENT));
+
+	if (opts->use_global_config + opts->use_system_config +
+	    opts->use_local_config + opts->use_worktree_config +
+	    !!opts->source.file + !!opts->source.blob > 1) {
+		error(_("only one config file at a time"));
+		exit(129);
+	}
+
+	if (!startup_info->have_repository) {
+		if (opts->use_local_config)
+			die(_("--local can only be used inside a git repository"));
+		if (opts->source.blob)
+			die(_("--blob can only be used inside a git repository"));
+		if (opts->use_worktree_config)
+			die(_("--worktree can only be used inside a git repository"));
+	}
+
+	if (opts->source.file &&
+			!strcmp(opts->source.file, "-")) {
+		opts->source.file = NULL;
+		opts->source.use_stdin = 1;
+		opts->source.scope = CONFIG_SCOPE_COMMAND;
+	}
+
+	if (opts->use_global_config) {
+		opts->source.file = opts->file_to_free = git_global_config();
+		if (!opts->source.file)
+			/*
+			 * It is unknown if HOME/.gitconfig exists, so
+			 * we do not know if we should write to XDG
+			 * location; error out even if XDG_CONFIG_HOME
+			 * is set and points at a sane location.
+			 */
+			die(_("$HOME not set"));
+		opts->source.scope = CONFIG_SCOPE_GLOBAL;
+	} else if (opts->use_system_config) {
+		opts->source.file = opts->file_to_free = git_system_config();
+		opts->source.scope = CONFIG_SCOPE_SYSTEM;
+	} else if (opts->use_local_config) {
+		opts->source.file = opts->file_to_free = repo_git_path(repo, "config");
+		opts->source.scope = CONFIG_SCOPE_LOCAL;
+	} else if (opts->use_worktree_config) {
+		struct worktree **worktrees = get_worktrees();
+		if (repo->repository_format_worktree_config)
+			opts->source.file = opts->file_to_free =
+				repo_git_path(repo, "config.worktree");
+		else if (worktrees[0] && worktrees[1])
+			die(_("--worktree cannot be used with multiple "
+			      "working trees unless the config\n"
+			      "extension worktreeConfig is enabled. "
+			      "Please read \"CONFIGURATION FILE\"\n"
+			      "section in \"git help worktree\" for details"));
+		else
+			opts->source.file = opts->file_to_free =
+				repo_git_path(repo, "config");
+		opts->source.scope = CONFIG_SCOPE_LOCAL;
+		free_worktrees(worktrees);
+	} else if (opts->source.file) {
+		if (!is_absolute_path(opts->source.file) && prefix)
+			opts->source.file = opts->file_to_free =
+				prefix_filename(prefix, opts->source.file);
+		opts->source.scope = CONFIG_SCOPE_COMMAND;
+	} else if (opts->source.blob) {
+		opts->source.scope = CONFIG_SCOPE_COMMAND;
+	}
+
+	if (opts->respect_includes_opt == -1)
+		opts->options.respect_includes = !opts->source.file;
+	else
+		opts->options.respect_includes = opts->respect_includes_opt;
+	if (startup_info->have_repository) {
+		opts->options.commondir = repo_get_common_dir(repo);
+		opts->options.git_dir = repo_get_git_dir(repo);
+	}
+}
+
+void location_options_release(struct config_location_options *opts)
+{
+	free(opts->file_to_free);
+}
diff --git a/config.h b/config.h
index 966a228f0e..6663964977 100644
--- a/config.h
+++ b/config.h
@@ -166,6 +166,26 @@ struct config_context {
 typedef int (*config_fn_t)(const char *, const char *,
 			   const struct config_context *, void *);
 
+struct config_location_options {
+	struct git_config_source source;
+	struct config_options options;
+	char *file_to_free;
+	int use_global_config;
+	int use_system_config;
+	int use_local_config;
+	int use_worktree_config;
+	int respect_includes_opt;
+};
+#define CONFIG_LOCATION_OPTIONS_INIT { \
+	.respect_includes_opt = -1, \
+}
+
+void location_options_init(struct repository *repo,
+			   struct config_location_options *opts,
+			   const char *prefix);
+
+void location_options_release(struct config_location_options *opts);
+
 /**
  * Read a specific file in git-config format.
  * This function takes the same callback and data parameters as `repo_config`.

diff --git a/builtin/config-batch.c b/builtin/config-batch.c
index 2c48c4ea37..9829b16c6f 100644
--- a/builtin/config-batch.c
+++ b/builtin/config-batch.c
@@ -67,9 +67,11 @@ static int command_parse_error(const char *command)
  * Return 0 on success.
  */
 typedef int (*command_fn)(struct repository *repo,
+			  const char *prefix,
 			  char *data, size_t data_len);
 
 static int unknown_command(struct repository *repo UNUSED,
+			   const char *prefix UNUSED,
 			   char *data UNUSED, size_t data_len UNUSED)
 {
 	return emit_response(UNKNOWN_COMMAND, NULL);
@@ -176,6 +178,7 @@ static size_t parse_token(char **data, size_t *data_len,
 }
 
 static int help_command_1(struct repository *repo,
+			  const char *prefix UNUSED,
 			  char *data, size_t data_len);
 
 enum value_match_mode {
@@ -292,6 +295,7 @@ static int parse_scope(const char *str, enum config_scope *scope)
  * [N*] indicates optional parameters that are not needed.
  */
 static int get_command_1(struct repository *repo,
+			 const char *prefix UNUSED,
 			 char *data,
 			 size_t data_len)
 {
@@ -402,6 +406,7 @@ static struct command commands[] = {
 #define COMMAND_COUNT ((size_t)(sizeof(commands) / sizeof(*commands)))
 
 static int help_command_1(struct repository *repo UNUSED,
+			  const char *prefix UNUSED,
 			  char *data UNUSED, size_t data_len UNUSED)
 {
 	struct strbuf fmt_str = STRBUF_INIT;
@@ -424,7 +429,8 @@ static int help_command_1(struct repository *repo UNUSED,
 	return 0;
 }
 
-static int process_command_nul(struct repository *repo)
+static int process_command_nul(struct repository *repo,
+			       const char *prefix)
 {
 	static struct strbuf line = STRBUF_INIT;
 	char *data, *command, *versionstr;
@@ -476,7 +482,7 @@ static int process_command_nul(struct repository *repo)
 		if (!commands[i].name[0] ||
 		    (!strcmp(command, commands[i].name) &&
 		     commands[i].version == version)) {
-			res = commands[i].fn(repo, data, data_len);
+			res = commands[i].fn(repo, prefix, data, data_len);
 			goto cleanup;
 		}
 	}
@@ -484,14 +490,15 @@ static int process_command_nul(struct repository *repo)
 	BUG(_("scanned to end of command list, including 'unknown_command'"));
 
 parse_error:
-	res = unknown_command(repo, NULL, 0);
+	res = unknown_command(repo, prefix, NULL, 0);
 
 cleanup:
 	strbuf_release(&line);
 	return res;
 }
 
-static int process_command_whitespace(struct repository *repo)
+static int process_command_whitespace(struct repository *repo,
+				      const char *prefix)
 {
 	static struct strbuf line = STRBUF_INIT;
 	struct string_list tokens = STRING_LIST_INIT_NODUP;
@@ -536,7 +543,7 @@ static int process_command_whitespace(struct repository *repo)
 		if (!commands[i].name[0] ||
 		    (!strcmp(command, commands[i].name) &&
 		     commands[i].version == version)) {
-			res = commands[i].fn(repo, data, data_len);
+			res = commands[i].fn(repo, prefix, data, data_len);
 			goto cleanup;
 		}
 	}
@@ -559,11 +566,12 @@ cleanup:
  *
  * Returns negative value on other catastrophic error.
  */
-static int process_command(struct repository *repo)
+static int process_command(struct repository *repo,
+			   const char *prefix)
 {
 	if (zformat)
-		return process_command_nul(repo);
-	return process_command_whitespace(repo);
+		return process_command_nul(repo, prefix);
+	return process_command_whitespace(repo, prefix);
 }
 
 int cmd_config_batch(int argc,
@@ -586,7 +594,7 @@ int cmd_config_batch(int argc,
 
 	repo_config(repo, git_default_config, NULL);
 
-	while (!(res = process_command(repo)));
+	while (!(res = process_command(repo, prefix)));
 
 	if (res == 1)
 		return 0;

Documentation/git-config-batch.adoc, builtin/config-batch.c, config.c, config.h, t/t1312-config-batch.sh

diff --git a/Documentation/git-config-batch.adoc b/Documentation/git-config-batch.adoc
index 3c9a3bb763..feec85c4ef 100644
--- a/Documentation/git-config-batch.adoc
+++ b/Documentation/git-config-batch.adoc
@@ -111,6 +111,30 @@ get 1 missing <key> [<value-pattern>|<value>]
 where `<value-pattern>` or `<value>` is only supplied if provided in
 the command.
 
+`set` version 1::
+	The `set` command writes a single key-value pair to a config
+	file. It specifies which file by a `<scope>` parameter from
+	among `system`, `global`, `local`, and `worktree`. The `<key>`
+	is the next positional argument. The remaining data in the line
+	is provided as the `<value>` to assign the config.
++
+------------
+set 1 <scope> <key> <value>
+------------
++
+These uses will match the behavior of `git config --set --<scope> <key>
+<value>`. Note that replacing all values with the `--all` option or
+matching specific value patterns are not supported by this command.
++
+The response of these commands will include a `success` message if the
+value is written as expected or `failed` if an unexpected failure
+occurs:
++
+------------
+set 1 success <scope> <key> <value>
+set 1 failed <scope> <key> <value>
+------------
+
 NUL-Terminated Format
 ~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/builtin/config-batch.c b/builtin/config-batch.c
index 9829b16c6f..373b0cad47 100644
--- a/builtin/config-batch.c
+++ b/builtin/config-batch.c
@@ -16,6 +16,7 @@ static int zformat = 0;
 #define UNKNOWN_COMMAND "unknown_command"
 #define HELP_COMMAND "help"
 #define GET_COMMAND "get"
+#define SET_COMMAND "set"
 #define COMMAND_PARSE_ERROR "command_parse_error"
 
 static void print_word(const char *word, int start)
@@ -379,6 +380,71 @@ cleanup:
 	return res;
 }
 
+
+/**
+ * 'set' command, version 1.
+ *
+ * Positional arguments should be of the form:
+ *
+ * [0] scope ("system", "global", "local", or "worktree")
+ * [1] config key
+ * [2] config value
+ */
+static int set_command_1(struct repository *repo,
+			 const char *prefix,
+			 char *data,
+			 size_t data_len)
+{
+	int res = 0, err = 0;
+	enum config_scope scope = CONFIG_SCOPE_UNKNOWN;
+	char *token = NULL, *key = NULL, *value = NULL;
+	struct config_location_options locopts = CONFIG_LOCATION_OPTIONS_INIT;
+
+	if (!parse_token(&data, &data_len, &token, &err) || err)
+		goto parse_error;
+
+	if (parse_scope(token, &scope) ||
+	    scope == CONFIG_SCOPE_UNKNOWN ||
+	    scope == CONFIG_SCOPE_SUBMODULE ||
+	    scope == CONFIG_SCOPE_COMMAND)
+		goto parse_error;
+
+	if (!parse_token(&data, &data_len, &key, &err) || err)
+		goto parse_error;
+
+	/* Use the remaining data as the value string. */
+	if (!zformat)
+		value = data;
+	else {
+		parse_token(&data, &data_len, &value, &err);
+		if (err)
+			goto parse_error;
+	}
+
+	if (location_options_set_scope(&locopts, scope))
+		goto parse_error;
+	location_options_init(repo, &locopts, prefix);
+
+	res = repo_config_set_in_file_gently(repo, locopts.source.file,
+					     key, NULL, value);
+
+	if (res)
+		res = emit_response(SET_COMMAND, "1", "failure",
+				    scope_str(scope), key, value, NULL);
+	else
+		res = emit_response(SET_COMMAND, "1", "success",
+				    scope_str(scope), key, value, NULL);
+
+	goto cleanup;
+
+parse_error:
+	res = command_parse_error(SET_COMMAND);
+
+cleanup:
+	location_options_release(&locopts);
+	return res;
+}
+
 struct command {
 	const char *name;
 	command_fn fn;
@@ -396,6 +462,11 @@ static struct command commands[] = {
 		.fn = get_command_1,
 		.version = 1,
 	},
+	{
+		.name = SET_COMMAND,
+		.fn = set_command_1,
+		.version = 1,
+	},
 	/* unknown_command must be last. */
 	{
 		.name = "",
diff --git a/config.c b/config.c
index 9f1a7b45cf..fa72234750 100644
--- a/config.c
+++ b/config.c
@@ -3594,6 +3594,33 @@ int lookup_config(const char **mapping, int nr_mapping, const char *var)
 	return -1;
 }
 
+int location_options_set_scope(struct config_location_options *opts,
+			       enum config_scope scope)
+{
+	switch (scope) {
+	case CONFIG_SCOPE_SYSTEM:
+		opts->use_system_config = 1;
+		break;
+
+	case CONFIG_SCOPE_GLOBAL:
+		opts->use_global_config = 1;
+		break;
+
+	case CONFIG_SCOPE_LOCAL:
+		opts->use_local_config = 1;
+		break;
+
+	case CONFIG_SCOPE_WORKTREE:
+		opts->use_worktree_config = 1;
+		break;
+
+	default:
+		return -1;
+	}
+
+	return 0;
+}
+
 void location_options_init(struct repository *repo,
 			   struct config_location_options *opts,
 			   const char *prefix)
diff --git a/config.h b/config.h
index 6663964977..f6432c1ec2 100644
--- a/config.h
+++ b/config.h
@@ -180,6 +180,9 @@ struct config_location_options {
 	.respect_includes_opt = -1, \
 }
 
+int location_options_set_scope(struct config_location_options *opts,
+			       enum config_scope scope);
+
 void location_options_init(struct repository *repo,
 			   struct config_location_options *opts,
 			   const char *prefix);
diff --git a/t/t1312-config-batch.sh b/t/t1312-config-batch.sh
index f7a74ddc2c..40f6f90ef2 100755
--- a/t/t1312-config-batch.sh
+++ b/t/t1312-config-batch.sh
@@ -47,9 +47,10 @@ test_expect_success 'help command' '
 	echo "help 1" >in &&
 
 	cat >expect <<-\EOF &&
-	help 1 count 2
+	help 1 count 3
 	help 1 help 1
 	help 1 get 1
+	help 1 set 1
 	EOF
 
 	git config-batch >out <in &&
@@ -63,9 +64,10 @@ test_expect_success 'help -z' '
 	EOF
 
 	cat >expect <<-\EOF &&
-	4:help 1:1 5:count 1:2
+	4:help 1:1 5:count 1:3
 	4:help 1:1 4:help 1:1
 	4:help 1:1 3:get 1:1
+	4:help 1:1 3:set 1:1
 	15:unknown_command
 	EOF
 
@@ -205,4 +207,92 @@ test_expect_success 'get config with -z' '
 	test_cmp expect out
 '
 
+test_expect_success 'set config by scope' '
+	test_when_finished git config remove-section test.set &&
+	GIT_CONFIG_SYSTEM=system-config-file &&
+	GIT_CONFIG_NOSYSTEM=0 &&
+	GIT_CONFIG_GLOBAL=global-config-file &&
+	export GIT_CONFIG_SYSTEM &&
+	export GIT_CONFIG_NOSYSTEM &&
+	export GIT_CONFIG_GLOBAL &&
+
+	cat >in <<-\EOF &&
+	set 1 system test.set.system system
+	set 1 global test.set.global global
+	set 1 local test.set.local local with spaces
+	set 1 worktree test.set.worktree worktree
+	set 1 submodule test.set.submodule submodule
+	set 1 command test.set.command command
+	set 1 inherited test.set.inherited inherited
+	EOF
+
+	cat >expect <<-\EOF &&
+	set 1 success system test.set.system system
+	set 1 success global test.set.global global
+	set 1 success local test.set.local local with spaces
+	set 1 success worktree test.set.worktree worktree
+	command_parse_error set
+	command_parse_error set
+	command_parse_error set
+	EOF
+
+	git config-batch <in >out 2>err &&
+
+	test_must_be_empty err &&
+	test_cmp expect out &&
+
+	cat >expect-values <<-EOF &&
+	file:system-config-file	system
+	file:global-config-file	global
+	file:.git/config	local with spaces
+	file:.git/config.worktree	worktree
+	EOF
+
+	git config get --show-origin --regexp --all test.set.* >values &&
+	test_cmp expect-values values
+'
+
+test_expect_success 'set config by scope with -z' '
+	test_when_finished git config remove-section test.set &&
+	GIT_CONFIG_SYSTEM=system-config-file &&
+	GIT_CONFIG_NOSYSTEM=0 &&
+	GIT_CONFIG_GLOBAL=global-config-file &&
+	export GIT_CONFIG_SYSTEM &&
+	export GIT_CONFIG_NOSYSTEM &&
+	export GIT_CONFIG_GLOBAL &&
+
+	cat >in <<-\EOF &&
+	3:set NUL 1:1 NUL 6:system NUL 15:test.set.system NUL 6:system NUL NUL
+	3:set NUL 1:1 NUL 6:global NUL 15:test.set.global NUL 6:global NUL NUL
+	3:set NUL 1:1 NUL 5:local NUL 14:test.set.local NUL 17:local with spaces NUL NUL
+	3:set NUL 1:1 NUL 8:worktree NUL 17:test.set.worktree NUL 8:worktree NUL NUL
+	3:set NUL 1:1 NUL 9:submodule NUL 18:test.set.submodule NUL 9:submodule NUL NUL
+	3:set NUL 1:1 NUL 7:command NUL 16:test.set.command NUL 7:command NUL NUL
+	3:set NUL 1:1 NUL 9:inherited NUL 18:test.set.inherited NUL 9:inherited NUL NUL
+	EOF
+
+	cat >expect <<-\EOF &&
+	3:set 1:1 7:success 6:system 15:test.set.system 6:system
+	3:set 1:1 7:success 6:global 15:test.set.global 6:global
+	3:set 1:1 7:success 5:local 14:test.set.local 17:local with spaces
+	3:set 1:1 7:success 8:worktree 17:test.set.worktree 8:worktree
+	19:command_parse_error 3:set
+	19:command_parse_error 3:set
+	19:command_parse_error 3:set
+	EOF
+
+	test_zformat git config-batch -z >out <in &&
+	test_cmp expect out &&
+
+	cat >expect-values <<-EOF &&
+	file:system-config-file	system
+	file:global-config-file	global
+	file:.git/config	local with spaces
+	file:.git/config.worktree	worktree
+	EOF
+
+	git config get --show-origin --regexp --all test.set.* >values &&
+	test_cmp expect-values values
+'
+
 test_done

diff --git a/t/t1312-config-batch.sh b/t/t1312-config-batch.sh
index 40f6f90ef2..11380f4247 100755
--- a/t/t1312-config-batch.sh
+++ b/t/t1312-config-batch.sh
@@ -295,4 +295,31 @@ test_expect_success 'set config by scope with -z' '
 	test_cmp expect-values values
 '
 
+test_expect_success 'read/write interactions in sequence' '
+	test_when_finished git config remove-section test.rw &&
+
+	cat >in <<-\EOF &&
+	get 1 local test.rw.missing
+	set 1 local test.rw.found found
+	get 1 local test.rw.found
+	set 1 local test.rw.found updated
+	get 1 local test.rw.found
+	EOF
+
+	cat >expect <<-\EOF &&
+	get 1 missing test.rw.missing
+	set 1 success local test.rw.found found
+	get 1 found test.rw.found local found
+	set 1 success local test.rw.found updated
+	get 1 found test.rw.found local updated
+	EOF
+
+	git config-batch <in >out 2>err &&
+
+	test_must_be_empty err &&
+	test_cmp expect out &&
+
+	test_cmp_config updated test.rw.found
+'
+
 test_done

Documentation/git-config-batch.adoc, builtin/config-batch.c, t/t1312-config-batch.sh

diff --git a/Documentation/git-config-batch.adoc b/Documentation/git-config-batch.adoc
index feec85c4ef..bdfd872d65 100644
--- a/Documentation/git-config-batch.adoc
+++ b/Documentation/git-config-batch.adoc
@@ -135,6 +135,34 @@ set 1 success <scope> <key> <value>
 set 1 failed <scope> <key> <value>
 ------------
 
+`unset` version 1::
+	The `unset` command removes a single value from a config file.
+	It specifies which file by a `<scope>` parameter from among
+	`system`, `global`, `local`, and `worktree`. The `<key>` is the
+	next positional argument. There could be two additional
+	arguments used to match specific config values, where the first
+	is either `arg:regex` or `arg:fixed-value` to specify the type
+	of match.
++
+------------
+unset 1 <scope> <key>
+unset 1 <scope> <key> arg:regex <value-pattern>
+unset 1 <scope> <key> arg:fixed-value <value>
+------------
++
+These uses will match the behavior of `git config --unset --<scope> <key>`
+with the additional arguments of `<value-pattern>` if `arg:regex` is
+given or `--fixed-value <value>` if `arg:fixed-value` is given.
++
+The response of these commands will include a `success` message
+if matched values are found and removed as expected or `failed` if an
+unexpected failure occurs:
++
+------------
+unset 1 success <scope> <key>
+unset 1 failed <scope> <key>
+------------
+
 NUL-Terminated Format
 ~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/builtin/config-batch.c b/builtin/config-batch.c
index 373b0cad47..25a942ba61 100644
--- a/builtin/config-batch.c
+++ b/builtin/config-batch.c
@@ -17,6 +17,7 @@ static int zformat = 0;
 #define HELP_COMMAND "help"
 #define GET_COMMAND "get"
 #define SET_COMMAND "set"
+#define UNSET_COMMAND "unset"
 #define COMMAND_PARSE_ERROR "command_parse_error"
 
 static void print_word(const char *word, int start)
@@ -445,6 +446,99 @@ cleanup:
 	return res;
 }
 
+/**
+ * 'unset' command, version 1.
+ *
+ * Positional arguments should be of the form:
+ *
+ * [0] scope ("system", "global", "local", or "worktree")
+ * [1] config key
+ * [2] config value
+ * [3*] match ("regex", "fixed-value")
+ * [4*] value regex OR value string
+ *
+ * [N*] indicates optional parameters that are not needed.
+ */
+static int unset_command_1(struct repository *repo,
+			 const char *prefix,
+			 char *data,
+			 size_t data_len)
+{
+	int res = 0, err = 0, flags = 0;
+	enum config_scope scope = CONFIG_SCOPE_UNKNOWN;
+	char *token = NULL, *key = NULL, *value_pattern = NULL;
+	size_t token_len;
+	struct config_location_options locopts = CONFIG_LOCATION_OPTIONS_INIT;
+
+	if (!parse_token(&data, &data_len, &token, &err) || err)
+		goto parse_error;
+
+	if (parse_scope(token, &scope) ||
+	    scope == CONFIG_SCOPE_UNKNOWN ||
+	    scope == CONFIG_SCOPE_SUBMODULE ||
+	    scope == CONFIG_SCOPE_COMMAND)
+		goto parse_error;
+
+	if (!parse_token(&data, &data_len, &key, &err) || err)
+		goto parse_error;
+
+	token_len = parse_token(&data, &data_len, &token, &err);
+	if (err)
+		goto parse_error;
+
+	if (token_len && !strncmp(token, "arg:", 4)) {
+		if (!strcmp(token + 4, "fixed-value"))
+			flags |= CONFIG_FLAGS_FIXED_VALUE;
+		/* no special logic for arg:regex. */
+		else if (strcmp(token + 4, "regex"))
+			goto parse_error; /* unknown arg. */
+
+		/* Use the remaining data as the value string. */
+		if (!zformat)
+			value_pattern = data;
+		else {
+			parse_token(&data, &data_len, &value_pattern, &err);
+			if (err)
+				goto parse_error;
+		}
+	} else if (token_len) {
+		/*
+		 * If we have remaining tokens not starting in "arg:",
+		 * then we don't understand them.
+		 */
+		goto parse_error;
+	}
+
+	if (location_options_set_scope(&locopts, scope))
+		goto parse_error;
+	location_options_init(repo, &locopts, prefix);
+
+	res = repo_config_set_multivar_in_file_gently(
+			repo,
+			locopts.source.file,
+			key,
+			/* value */ NULL,
+			value_pattern,
+			/* comment */ NULL,
+			flags);
+
+	if (res)
+		res = emit_response(UNSET_COMMAND, "1", "failure",
+				    scope_str(scope), key, NULL);
+	else
+		res = emit_response(UNSET_COMMAND, "1", "success",
+				    scope_str(scope), key, NULL);
+
+	goto cleanup;
+
+parse_error:
+	res = command_parse_error(UNSET_COMMAND);
+
+cleanup:
+	location_options_release(&locopts);
+	return res;
+}
+
 struct command {
 	const char *name;
 	command_fn fn;
@@ -467,6 +561,11 @@ static struct command commands[] = {
 		.fn = set_command_1,
 		.version = 1,
 	},
+	{
+		.name = UNSET_COMMAND,
+		.fn = unset_command_1,
+		.version = 1,
+	},
 	/* unknown_command must be last. */
 	{
 		.name = "",
diff --git a/t/t1312-config-batch.sh b/t/t1312-config-batch.sh
index 11380f4247..3bddbc0de3 100755
--- a/t/t1312-config-batch.sh
+++ b/t/t1312-config-batch.sh
@@ -47,10 +47,11 @@ test_expect_success 'help command' '
 	echo "help 1" >in &&
 
 	cat >expect <<-\EOF &&
-	help 1 count 3
+	help 1 count 4
 	help 1 help 1
 	help 1 get 1
 	help 1 set 1
+	help 1 unset 1
 	EOF
 
 	git config-batch >out <in &&
@@ -64,10 +65,11 @@ test_expect_success 'help -z' '
 	EOF
 
 	cat >expect <<-\EOF &&
-	4:help 1:1 5:count 1:3
+	4:help 1:1 5:count 1:4
 	4:help 1:1 4:help 1:1
 	4:help 1:1 3:get 1:1
 	4:help 1:1 3:set 1:1
+	4:help 1:1 5:unset 1:1
 	15:unknown_command
 	EOF
 
@@ -295,15 +297,60 @@ test_expect_success 'set config by scope with -z' '
 	test_cmp expect-values values
 '
 
-test_expect_success 'read/write interactions in sequence' '
-	test_when_finished git config remove-section test.rw &&
+test_expect_success 'unset config by scope and filter' '
+	GIT_CONFIG_SYSTEM=system-config-file &&
+	GIT_CONFIG_NOSYSTEM=0 &&
+	GIT_CONFIG_GLOBAL=global-config-file &&
+	export GIT_CONFIG_SYSTEM &&
+	export GIT_CONFIG_NOSYSTEM &&
+	export GIT_CONFIG_GLOBAL &&
+
+	cat >in <<-\EOF &&
+	set 1 system test.unset.key system
+	set 1 global test.unset.key global
+	set 1 local test.unset.key local with spaces
+	set 1 worktree test.unset.key worktree
+	unset 1 system test.unset.key
+	unset 1 global test.unset.key arg:regex g.*
+	unset 1 local test.unset.key arg:fixed-value local with spaces
+	unset 1 worktree test.unset.key arg:fixed-value submodule
+	unset 1 worktree test.unset.key arg:regex l.*
+	EOF
+
+	cat >expect <<-\EOF &&
+	set 1 success system test.unset.key system
+	set 1 success global test.unset.key global
+	set 1 success local test.unset.key local with spaces
+	set 1 success worktree test.unset.key worktree
+	unset 1 success system test.unset.key
+	unset 1 success global test.unset.key
+	unset 1 success local test.unset.key
+	unset 1 failure worktree test.unset.key
+	unset 1 failure worktree test.unset.key
+	EOF
+
+	git config-batch <in >out 2>err &&
 
+	test_must_be_empty err &&
+	test_cmp expect out &&
+
+	cat >expect-values <<-EOF &&
+	file:.git/config.worktree	worktree
+	EOF
+
+	git config get --show-origin --regexp --all test.unset.key >values &&
+	test_cmp expect-values values
+'
+
+test_expect_success 'read/write interactions in sequence' '
 	cat >in <<-\EOF &&
 	get 1 local test.rw.missing
 	set 1 local test.rw.found found
 	get 1 local test.rw.found
 	set 1 local test.rw.found updated
 	get 1 local test.rw.found
+	unset 1 local test.rw.found arg:fixed-value updated
+	get 1 local test.rw.found
 	EOF
 
 	cat >expect <<-\EOF &&
@@ -312,14 +359,14 @@ test_expect_success 'read/write interactions in sequence' '
 	get 1 found test.rw.found local found
 	set 1 success local test.rw.found updated
 	get 1 found test.rw.found local updated
+	unset 1 success local test.rw.found
+	get 1 missing test.rw.found
 	EOF
 
 	git config-batch <in >out 2>err &&
 
 	test_must_be_empty err &&
-	test_cmp expect out &&
-
-	test_cmp_config updated test.rw.found
+	test_cmp expect out
 '
 
 test_done