objects). There are currently four different object types: "blob",
"tree", "commit" and "tag".
-A "blob" object cannot refer to any other object, and is, like the tag
+A "blob" object cannot refer to any other object, and is, like the type
implies, a pure storage object containing some user data. It is used to
actually store the file data, i.e. a blob object is associated with some
particular version of some file.
Regardless of object type, all objects share the following
characteristics: they are all deflated with zlib, and have a header
-that not only specifies their tag, but also provides size information
+that not only specifies their type, but also provides size information
about the data in the object. It's worth noting that the SHA1 hash
that is used to name the object is the hash of the original data
plus this header, so `sha1sum` 'file' does not match the object name
independently of the contents or the type of the object: all objects can
be validated by verifying that (a) their hashes match the content of the
file and (b) the object successfully inflates to a stream of bytes that
-forms a sequence of <ascii t
ag without space> + <space> + <ascii decimal
+forms a sequence of <ascii t
ype without space> + <space> + <ascii decimal
size> + <byte\0> + <binary object data>.
The structured objects can further have their structure and
i.e. it will normally just update existing cache entries.
To tell git that yes, you really do realize that certain files no
-longer exist in the archive, or that new files should be added, you
+longer exist, or that new files should be added, you
should use the `--remove` and `--add` flags respectively.
NOTE! A `--remove` flag does 'not' mean that subsequent filenames will
that commit, and you should save it away for later use. Normally,
you'd commit a new `HEAD` state, and while git doesn't care where you
save the note about that state, in practice we tend to just write the
-result to the file `.git/HEAD`, so that we can always see what the
-last committed state was.
+result to the file pointed at by `.git/HEAD`, so that we can always see
+what the last committed state was.
+
+Here is an ASCII art by Jon Loeliger that illustrates how
+various pieces fit together.
+
+------------
+
+ commit-tree
+ commit obj
+ +----+
+ | |
+ | |
+ V V
+ +-----------+
+ | Object DB |
+ | Backing |
+ | Store |
+ +-----------+
+ ^
+ write-tree | |
+ tree obj | |
+ | | read-tree
+ | | tree obj
+ V
+ +-----------+
+ | Index |
+ | "cache" |
+ +-----------+
+ update-index ^
+ blob obj | |
+ | |
+ checkout-index -u | | checkout-index
+ stat | | blob obj
+ V
+ +-----------+
+ | Working |
+ | Directory |
+ +-----------+
+
+------------
+
6) Examining the data
~~~~~~~~~~~~~~~~~~~~~
follow the convention of having the top commit name in `.git/HEAD`,
you can do
- git-cat-file commit $(cat .git/HEAD)
+ git-cat-file commit HEAD
to see what the top commit was.
Historical note. We did not have `-u` facility when this
section was first written, so we used to warn that
the merge is done in the index file, not in your
-working directory, and your working directory will no longer match your
-index.
+working tree, and your working tree will not match your
+index after this step.
+This is no longer true. The above command, thanks to `-u`
+option, updates your working tree with the merge results for
+paths that have been trivially merged.
8) Merging multiple trees, continued
to help you understand what conceptually happens under the hood.
In practice, nobody, not even git itself, uses three `git-cat-file`
for this. There is `git-merge-index` program that extracts the
-stages to temporary files and calls a `merge` script on it
+stages to temporary files and calls a "merge" script on it:
git-merge-index git-merge-one-file hello.c