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object::
The unit of storage in GIT. It is uniquely identified by
the SHA1 of its contents. Consequently, an object can not
be changed.
SHA1::
A 20-byte sequence (or 41-byte file containing the hex
representation and a newline). It is calculated from the
contents of an object by the Secure Hash Algorithm 1.
object database::
Stores a set of "objects", and an individial object is identified
by its SHA1 (its ref). The objects are either stored as single
files, or live inside of packs.
object name::
Synonym for SHA1.
blob object::
Untyped object, i.e. the contents of a file.
tree object::
An object containing a list of blob and/or tree objects.
(A tree usually corresponds to a directory without
subdirectories).
tree::
Either a working tree, or a tree object together with the
dependent blob and tree objects (i.e. a stored representation
of a working tree).
cache::
A collection of files whose contents are stored as objects.
The cache is a stored version of your working tree. Well, can
also contain a second, and even a third version of a working
tree, which are used when merging.
cache entry::
The information regarding a particular file, stored in the index.
A cache entry can be unmerged, if a merge was started, but not
yet finished (i.e. if the cache contains multiple versions of
that file).
index::
Contains information about the cache contents, in particular
timestamps and mode flags ("stat information") for the files
stored in the cache. An unmerged index is an index which contains
unmerged cache entries.
working tree::
The set of files and directories currently being worked on.
Think "ls -laR"
directory::
The list you get with "ls" :-)
checkout::
The action of updating the working tree to a revision which was
stored in the object database.
revision::
A particular state of files and directories which was stored in
the object database. It is referenced by a commit object.
commit::
The action of storing the current state of the cache in the
object database. The result is a revision.
commit object::
An object which contains the information about a particular
revision, such as parents, committer, author, date and the
tree object which corresponds to the top directory of the
stored revision.
changeset::
BitKeeper/cvsps speak for "commit". Since git does not store
changes, but states, it really does not make sense to use
the term "changesets" with git.
ent::
Favorite synonym to "tree-ish" by some total geeks.
clean::
A working tree is clean, if it corresponds to the revision
referenced by the current head.
dirty::
A working tree is said to be dirty if it contains modifications
which have not been committed to the current branch.
head::
The top of a branch. It contains a ref to the corresponding
commit object.
branch::
A non-cyclical graph of revisions, i.e. the complete history of
a particular revision, which does not (yet) have children, which
is called the branch head. The branch heads are stored in
$GIT_DIR/refs/heads/.
ref::
A 40-byte hex representation of a SHA1 pointing to a particular
object. These are stored in $GIT_DIR/refs/.
head ref::
A ref pointing to a head. Often, this is abbreviated to "head".
Head refs are stored in $GIT_DIR/refs/heads/.
tree-ish::
A ref pointing to either a commit object, a tree object, or a
tag object pointing to a commit or tree object.
tag object::
An object containing a ref pointing to another object. It can
contain a (PGP) signature, in which case it is called "signed
tag object".
tag::
A ref pointing to a tag or commit object. In contrast to a head,
a tag is not changed by a commit. Tags (not tag objects) are
stored in $GIT_DIR/refs/tags/. A git tag has nothing to do with
a Lisp tag (which is called object type in git's context).
merge::
To merge branches means to try to accumulate the changes since a
common ancestor and apply them to the first branch. An automatic
merge uses heuristics to accomplish that. Evidently, an automatic
merge can fail.
resolve::
The action of fixing up manually what a failed automatic merge
left behind.
repository::
A collection of refs together with an object database containing
all objects, which are reachable from the refs. A repository can
share an object database with other repositories.
alternate object database::
Via the alternates mechanism, a repository can inherit part of its
object database from another object database, which is called
"alternate".
reachable::
An object is reachable from a ref/commit/tree/tag, if there is a
chain leading from the latter to the former.
chain::
A list of objects, where each object in the list contains a
reference to its successor (for example, the successor of a commit
could be one of its parents).
parent::
A commit object contains a (possibly empty) list of the logical
predecessor(s) in the line of development, i.e. its parents.
fetch::
Fetching a branch means to get the branch's head ref from a
remote repository, to find out which objects are missing from
the local object database, and to get them, too.
pull::
Pulling a branch means to fetch it and merge it.
push::
Pushing a branch means to get the branch's head ref from a remote
repository, find out if it is an ancestor to the branch's local
head ref is a direct, and in that case, putting all objects, which
are reachable from the local head ref, and which are missing from
the remote repository, into the remote object database, and updating
the remote head ref. If the remote head is not an ancestor to the
local head, the push fails.
pack::
A set of objects which have been compressed into one file (to save
space or to transmit them efficiently).
pack index::
Contains offsets into a pack, so the pack can be used instead of
the unpacked objects.
plumbing::
Cute name for core git.
porcelain::
Cute name for programs and program suites depending on core git,
presenting a high level access to core git. Porcelains expose
more of a SCM interface than the plumbing.
object type:
One of the identifiers "commit","tree","tag" and "blob" describing
the type of an object.
SCM::
Source code management (tool).
dircache::
You are *waaaaay* behind.
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