Add "unpack-file" helper that unpacks a sha1 blob into a tmpfile.

unpack-file.c

@@ -0,0 +1,34 @@
+#include "cache.h"
+
+static char *create_temp_file(unsigned char *sha1)
+{
+	static char path[50];
+	void *buf;
+	char type[100];
+	unsigned long size;
+	int fd;
+
+	buf = read_sha1_file(sha1, type, &size);
+	if (!buf || strcmp(type, "blob"))
+		die("unable to read blob object %s", sha1_to_hex(sha1));
+
+	strcpy(path, ".merge_file_XXXXXX");
+	fd = mkstemp(path);
+	if (fd < 0)
+		die("unable to create temp-file");
+	if (write(fd, buf, size) != size)
+		die("unable to write temp-file");
+	close(fd);
+	return path;
+}
+
+int main(int argc, char **argv)
+{
+	unsigned char sha1[20];
+
+	if (argc != 2 || get_sha1_hex(argv[1], sha1))
+		usage("unpack-file.c <sha1>");
+
+	puts(create_temp_file(sha1));
+	return 0;
+}