Add git-config-set, a simple helper for scripts to set config variables

This is meant for the end user, who cannot be expected to edit
.git/config by hand.

Example:

	git-config-set core.filemode true

will set filemode in the section [core] to true,

	git-config-set --unset core.filemode

will remove the entry (failing if it is not there), and

	git-config-set --unset diff.twohead ^recar

will remove the unique entry whose value matches the regex "^recar"
(failing if there is no unique such entry).

It is just a light wrapper around git_config_set() and
git_config_set_multivar().

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

.gitignore

@@ -17,6 +17,7 @@ git-clone
 git-clone-pack
 git-commit
 git-commit-tree
+git-config-set
 git-convert-objects
 git-count-objects
 git-cvsexportcommit

Makefile

@@ -125,7 +125,8 @@ PROGRAMS = \
 	git-unpack-objects$X git-update-index$X git-update-server-info$X \
 	git-upload-pack$X git-verify-pack$X git-write-tree$X \
 	git-update-ref$X git-symbolic-ref$X git-check-ref-format$X \
-	git-name-rev$X git-pack-redundant$X git-var$X $(SIMPLE_PROGRAMS)
+	git-name-rev$X git-pack-redundant$X git-config-set$X git-var$X \
+	$(SIMPLE_PROGRAMS)
 
 # Backward compatibility -- to be removed after 1.0
 PROGRAMS += git-ssh-pull$X git-ssh-push$X

config-set.c

@@ -0,0 +1,26 @@
+#include "cache.h"
+
+static const char git_config_set_usage[] =
+"git-config-set name [value [value_regex]] | --unset name [value_regex]";
+
+int main(int argc, const char **argv)
+{
+	setup_git_directory();
+	switch (argc) {
+	case 2:
+		return git_config_set(argv[1], NULL);
+	case 3:
+		if (!strcmp(argv[1], "--unset"))
+			return git_config_set(argv[2], NULL);
+		else
+			return git_config_set(argv[1], argv[2]);
+	case 4:
+		if (!strcmp(argv[1], "--unset"))
+			return git_config_set_multivar(argv[2], NULL, argv[3]);
+		else
+			return git_config_set_multivar(argv[1], argv[2], argv[3]);
+	default:
+		usage(git_config_set_usage);
+	}
+	return 0;
+}