config: add '--name-only' option to list only variable names

'git config' can only show values or name-value pairs, so if a shell
script needs the names of set config variables it has to run 'git config
--list' or '--get-regexp' and parse the output to separate config
variable names from their values.  However, such a parsing can't cope
with multi-line values.  Though 'git config' can produce null-terminated
output for newline-safe parsing, that's of no use in such a case, becase
shells can't cope with null characters.

Even our own bash completion script suffers from these issues.

Help the completion script, and shell scripts in general, by introducing
the '--name-only' option to modify the output of '--list' and
'--get-regexp' to list only the names of config variables, so they don't
have to perform error-prone post processing to separate variable names
from their values anymore.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-config.txt

@@ -14,13 +14,13 @@ SYNOPSIS
 'git config' [<file-option>] [type] --replace-all name value [value_regex]
 'git config' [<file-option>] [type] [-z|--null] --get name [value_regex]
 'git config' [<file-option>] [type] [-z|--null] --get-all name [value_regex]
-'git config' [<file-option>] [type] [-z|--null] --get-regexp name_regex [value_regex]
+'git config' [<file-option>] [type] [-z|--null] [--name-only] --get-regexp name_regex [value_regex]
 'git config' [<file-option>] [type] [-z|--null] --get-urlmatch name URL
 'git config' [<file-option>] --unset name [value_regex]
 'git config' [<file-option>] --unset-all name [value_regex]
 'git config' [<file-option>] --rename-section old_name new_name
 'git config' [<file-option>] --remove-section name
-'git config' [<file-option>] [-z|--null] -l | --list
+'git config' [<file-option>] [-z|--null] [--name-only] -l | --list
 'git config' [<file-option>] --get-color name [default]
 'git config' [<file-option>] --get-colorbool name [stdout-is-tty]
 'git config' [<file-option>] -e | --edit
@@ -159,7 +159,7 @@ See also <<FILES>>.
 
 -l::
 --list::
-	List all variables set in config file.
+	List all variables set in config file, along with their values.
 
 --bool::
 	'git config' will ensure that the output is "true" or "false"
@@ -190,6 +190,10 @@ See also <<FILES>>.
 	output without getting confused e.g. by values that
 	contain line breaks.
 
+--name-only::
+	Output only the names of config variables for `--list` or
+	`--get-regexp`.
+
 --get-colorbool name [stdout-is-tty]::
 
 	Find the color setting for `name` (e.g. `color.diff`) and output

builtin/config.c

@@ -13,6 +13,7 @@ static char *key;
 static regex_t *key_regexp;
 static regex_t *regexp;
 static int show_keys;
+static int omit_values;
 static int use_key_regexp;
 static int do_all;
 static int do_not_match;
@@ -78,6 +79,7 @@ static struct option builtin_config_options[] = {
 	OPT_BIT(0, "path", &types, N_("value is a path (file or directory name)"), TYPE_PATH),
 	OPT_GROUP(N_("Other")),
 	OPT_BOOL('z', "null", &end_null, N_("terminate values with NUL byte")),
+	OPT_BOOL(0, "name-only", &omit_values, N_("show variable names only")),
 	OPT_BOOL(0, "includes", &respect_includes, N_("respect include directives on lookup")),
 	OPT_END(),
 };
@@ -91,7 +93,7 @@ static void check_argc(int argc, int min, int max) {
 
 static int show_all_config(const char *key_, const char *value_, void *cb)
 {
-	if (value_)
+	if (!omit_values && value_)
 		printf("%s%c%s%c", key_, delim, value_, term);
 	else
 		printf("%s%c", key_, term);
@@ -117,6 +119,10 @@ static int format_config(struct strbuf *buf, const char *key_, const char *value
 		strbuf_addstr(buf, key_);
 		must_print_delim = 1;
 	}
+	if (omit_values) {
+		strbuf_addch(buf, term);
+		return 0;
+	}
 	if (types == TYPE_INT)
 		sprintf(value, "%"PRId64,
 			git_config_int64(key_, value_ ? value_ : ""));
@@ -549,7 +555,11 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 		default:
 			usage_with_options(builtin_config_usage, builtin_config_options);
 		}
-
+	if (omit_values &&
+	    !(actions == ACTION_LIST || actions == ACTION_GET_REGEXP)) {
+		error("--name-only is only applicable to --list or --get-regexp");
+		usage_with_options(builtin_config_usage, builtin_config_options);
+	}
 	if (actions == ACTION_LIST) {
 		check_argc(argc, 0, 0);
 		if (git_config_with_options(show_all_config, NULL,

contrib/completion/git-completion.bash

@@ -1887,6 +1887,7 @@ _git_config ()
 			--get --get-all --get-regexp
 			--add --unset --unset-all
 			--remove-section --rename-section
+			--name-only
 			"
 		return
 		;;

t/t1300-repo-config.sh

@@ -352,6 +352,18 @@ test_expect_success '--list without repo produces empty output' '
 	test_cmp expect output
 '
 
+cat > expect << EOF
+beta.noindent
+nextsection.nonewline
+123456.a123
+version.1.2.3eX.alpha
+EOF
+
+test_expect_success '--name-only --list' '
+	git config --name-only --list >output &&
+	test_cmp expect output
+'
+
 cat > expect << EOF
 beta.noindent sillyValue
 nextsection.nonewline wow2 for me
@@ -362,6 +374,16 @@ test_expect_success '--get-regexp' '
 	test_cmp expect output
 '
 
+cat > expect << EOF
+beta.noindent
+nextsection.nonewline
+EOF
+
+test_expect_success '--name-only --get-regexp' '
+	git config --name-only --get-regexp in >output &&
+	test_cmp expect output
+'
+
 cat > expect << EOF
 wow2 for me
 wow4 for you