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

Makefile

@@ -15,7 +15,7 @@ AR=ar
 
 PROG=   update-cache show-diff init-db write-tree read-tree commit-tree \
 	cat-file fsck-cache checkout-cache diff-tree rev-tree show-files \
-	check-files ls-tree merge-base merge-cache
+	check-files ls-tree merge-base merge-cache unpack-file
 
 all: $(PROG)
 
@@ -78,6 +78,9 @@ merge-base: merge-base.o $(LIB_FILE) object.o commit.o tree.o blob.o
 merge-cache: merge-cache.o $(LIB_FILE)
 	$(CC) $(CFLAGS) -o merge-cache merge-cache.o $(LIBS)
 
+unpack-file: unpack-file.o $(LIB_FILE)
+	$(CC) $(CFLAGS) -o unpack-file unpack-file.o $(LIBS)
+
 blob.o: $(LIB_H)
 cat-file.o: $(LIB_H)
 check-files.o: $(LIB_H)
@@ -100,6 +103,7 @@ show-files.o: $(LIB_H)
 tree.o: $(LIB_H)
 update-cache.o: $(LIB_H)
 usage.o: $(LIB_H)
+unpack-file.o: $(LIB_H)
 write-tree.o: $(LIB_H)
 
 clean:

unpack-file.c

+#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;
+}