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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.
object name::
The unique identifier of an object. The hash of the object's contents
using the Secure Hash Algorithm 1 and usually represented by the 40
character hexadecimal encoding of the hash of the object (possibly
followed by a white space).
SHA1::
Synonym for object name.
object identifier::
Synonym for object name.
hash::
In git's context, synonym to object name.
object database::
Stores a set of "objects", and an individial object is identified
by its object name. The objects usually live in `$GIT_DIR/objects/`.
blob object::
Untyped object, e.g. the contents of a file.
tree object::
An object containing a list of file names and modes along with refs
to the associated blob and/or tree objects. A tree is equivalent
to a directory.
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).
DAG::
Directed acyclic graph. The commit objects form a directed acyclic
graph, because they have parents (directed), and the graph of commit
objects is acyclic (there is no chain which begins and ends with the
same object).
index::
A collection of files with stat information, whose contents are
stored as objects. The index is a stored version of your working
tree. Truth be told, it can also contain a second, and even a third
version of a working tree, which are used when merging.
index entry::
The information regarding a particular file, stored in the index.
An index entry can be unmerged, if a merge was started, but not
yet finished (i.e. if the index contains multiple versions of
that file).
unmerged index:
An index which contains unmerged index entries.
cache::
Obsolete for: index.
working tree::
The set of files and directories currently being worked on,
i.e. you can work in your working tree without using git at all.
directory::
The list you get with "ls" :-)
revision::
A particular state of files and directories which was stored in
the object database. It is referenced by a commit object.
checkout::
The action of updating the working tree to a revision which was
stored in the object database.
commit::
As a verb: The action of storing the current state of the index in the
object database. The result is a revision.
As a noun: Short hand for commit object.
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.
parent::
A commit object contains a (possibly empty) list of the logical
predecessor(s) in the line of development, i.e. its parents.
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.
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 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 may be 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 tag or commit or tree object.
ent::
Favorite synonym to "tree-ish" by some total geeks. See
`http://en.wikipedia.org/wiki/Ent_(Middle-earth)` for an in-depth
explanation.
tag object::
An object containing a ref pointing to another object, which can
contain a message just like a commit object. It can also
contain a (PGP) signature, in which case it is called a "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).
A tag is most typically used to mark a particular point in the
commit ancestry chain.
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.
octopus::
To merge more than two branches. Also denotes an intelligent
predator.
resolve::
The action of fixing up manually what a failed automatic merge
left behind.
rewind::
To throw away part of the development, i.e. to assign the head to
an earlier revision.
rebase::
To clean a branch by starting from the head of the main line of
development ("master"), and reapply the (possibly cherry-picked)
changes from that branch.
repository::
A collection of refs together with an object database containing
all objects, which are reachable from the refs, possibly accompanied
by meta data from one or more porcelains. A repository can
share an object database with other repositories.
git archive::
Synonym for repository (for arch people).
file system::
Linus Torvalds originally designed git to be a user space file
system, i.e. the infrastructure to hold files and directories.
That ensured the efficiency and speed of git.
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).
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::
The list of identifiers, and other information, of the objects in a
pack, to assist in efficiently accessing the contents of a pack.
core git::
Fundamental data structures and utilities of git. Exposes only
limited source code management tools.
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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