GITGLOSSARY(7)GITGLOSSARY(7)NAMEgitglossary - A GIT Glossary
SYNOPSIS
*
DESCRIPTION
alternate object database
Via the alternates mechanism, a repository can inherit part of
its object database from another object database, which is
called "alternate".
bare repository
A bare repository is normally an appropriately named directory
with a .git suffix that does not have a locally checked-out copy
of any of the files under revision control. That is, all of the
git administrative and control files that would normally be pre-
sent in the hidden .git sub-directory are directly present in
the repository.git directory instead, and no other files are
present and checked out. Usually publishers of public reposito-
ries make bare repositories available.
blob object
Untyped object, e.g. the contents of a file.
branch A "branch" is an active line of development. The most recent
commit on a branch is referred to as the tip of that branch. The
tip of the branch is referenced by a branch head, which moves
forward as additional development is done on the branch. A sin-
gle git repository can track an arbitrary number of branches,
but your working tree is associated with just one of them (the
"current" or "checked out" branch), and HEAD points to that
branch.
cache Obsolete for: index.
chain A list of objects, where each object in the list contains a ref-
erence to its successor (for example, the successor of a commit
could be one of 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.
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checkout
The action of updating all or part of the working tree with a
tree object or blob from the object database, and updating the
index and HEAD if the whole working tree has been pointed at a
new branch.
cherry-picking
In SCM jargon, "cherry pick" means to choose a subset of changes
out of a series of changes (typically commits) and record them
as a new series of changes on top of a different codebase. In
GIT, this is performed by the "git cherry-pick" command to
extract the change introduced by an existing commit and to
record it based on the tip of the current branch as a new com-
mit.
clean A working tree is clean, if it corresponds to the revision ref-
erenced by the current head. Also see "dirty".
commit As a noun: A single point in the git history; the entire history
of a project is represented as a set of interrelated commits.
The word "commit" is often used by git in the same places other
revision control systems use the words "revision" or "version".
Also used as a short hand for commit object.
As a verb: The action of storing a new snapshot of the pro-
ject’s state in the git history, by creating a new commit
representing the current state of the index and advancing HEAD
to point at the new commit.
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.
core git
Fundamental data structures and utilities of git. Exposes only
limited source code management tools.
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).
dangling object
An unreachable object which is not reachable even from other
unreachable objects; a dangling object has no references to it
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from any reference or object in the repository.
detached HEAD
Normally the HEAD stores the name of a branch. However, git also
allows you to check out an arbitrary commit that isn’t
necessarily the tip of any particular branch. In this case HEAD
is said to be "detached".
dircache
You are waaaaay behind. See index.
directory
The list you get with "ls" :-)
dirty A working tree is said to be "dirty" if it contains modifica-
tions which have not been committed to the current branch.
ent Favorite synonym to "tree-ish" by some total geeks. See
http://en.wikipedia.org/wiki/Ent_(Middle-earth) for an in-depth
explanation. Avoid this term, not to confuse people.
evil merge
An evil merge is a merge that introduces changes that do not
appear in any parent.
fast-forward
A fast-forward is a special type of merge where you have a revi-
sion and you are "merging" another branch's changes that happen
to be a descendant of what you have. In such these cases, you do
not make a new merge commit but instead just update to his
revision. This will happen frequently on a tracking branch of a
remote repository.
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. See also
git-fetch(1).
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.
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git archive
Synonym for repository (for arch people).
grafts Grafts enables two otherwise different lines of development to
be joined together by recording fake ancestry information for
commits. This way you can make git pretend the set of parents a
commit has is different from what was recorded when the commit
was created. Configured via the .git/info/grafts file.
hash In git’s context, synonym to object name.
head A named reference to the commit at the tip of a branch. Heads
are stored in $GIT_DIR/refs/heads/, except when using packed
refs. (See git-pack-refs(1).)
HEAD The current branch. In more detail: Your working tree is nor-
mally derived from the state of the tree referred to by HEAD.
HEAD is a reference to one of the heads in your repository,
except when using a detached HEAD, in which case it may refer-
ence an arbitrary commit.
head ref
A synonym for head.
hook During the normal execution of several git commands, call-outs
are made to optional scripts that allow a developer to add func-
tionality or checking. Typically, the hooks allow for a command
to be pre-verified and potentially aborted, and allow for a
post-notification after the operation is done. The hook scripts
are found in the $GIT_DIR/hooks/ directory, and are enabled by
simply removing the .sample suffix from the filename. In earlier
versions of git you had to make them executable.
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 ver-
sions of that file).
master The default development branch. Whenever you create a git
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repository, a branch named "master" is created, and becomes the
active branch. In most cases, this contains the local develop-
ment, though that is purely by convention and is not required.
merge As a verb: To bring the contents of another branch (possibly
from an external repository) into the current branch. In the
case where the merged-in branch is from a different repository,
this is done by first fetching the remote branch and then merg-
ing the result into the current branch. This combination of
fetch and merge operations is called a pull. Merging is per-
formed by an automatic process that identifies changes made
since the branches diverged, and then applies all those changes
together. In cases where changes conflict, manual intervention
may be required to complete the merge.
As a noun: unless it is a fast-forward, a successful merge
results in the creation of a new commit representing the result
of the merge, and having as parents the tips of the merged
branches. This commit is referred to as a "merge commit", or
sometimes just a "merge".
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 database
Stores a set of "objects", and an individual object is identi-
fied by its object name. The objects usually live in
$GIT_DIR/objects/.
object identifier
Synonym for object name.
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.
object type
One of the identifiers "commit", "tree", "tag" or "blob"
describing the type of an object.
octopus
To merge more than two branches. Also denotes an intelligent
predator.
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origin The default upstream repository. Most projects have at least one
upstream project which they track. By default origin is used for
that purpose. New upstream updates will be fetched into remote
tracking branches named origin/name-of-upstream-branch, which
you can see using git branch -r.
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.
parent A commit object contains a (possibly empty) list of the logical
predecessor(s) in the line of development, i.e. its parents.
pickaxe
The term pickaxe refers to an option to the diffcore routines
that help select changes that add or delete a given text string.
With the --pickaxe-all option, it can be used to view the full
changeset that introduced or removed, say, a particular line of
text. See git-diff(1).
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.
pull Pulling a branch means to fetch it and merge it. See also
git-pull(1).
push Pushing a branch means to get the branch’s head ref from a
remote repository, find out if it is a direct ancestor to the
branch’s local head ref, 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.
reachable
All of the ancestors of a given commit are said to be
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"reachable" from that commit. More generally, one object is
reachable from another if we can reach the one from the other by
a chain that follows tags to whatever they tag, commits to their
parents or trees, and trees to the trees or blobs that they con-
tain.
rebase To reapply a series of changes from a branch to a different
base, and reset the head of that branch to the result.
ref A 40-byte hex representation of a SHA1 or a name that denotes a
particular object. These may be stored in $GIT_DIR/refs/.
reflog A reflog shows the local "history" of a ref. In other words, it
can tell you what the 3rd last revision in this repository was,
and what was the current state in this repository, yesterday
9:14pm. See git-reflog(1) for details.
refspec
A "refspec" is used by fetch and push to describe the mapping
between remote ref and local ref. They are combined with a colon
in the format <src>:<dst>, preceded by an optional plus sign, +.
For example: git fetch $URL refs/heads/master:refs/heads/origin
means "grab the master branch head from the $URL and store it
as my origin branch head". And git push $URL refs/heads/mas-
ter:refs/heads/to-upstream means "publish my master branch head
as to-upstream branch at $URL". See also git-push(1).
repository
A collection of refs together with an object database containing
all objects which are reachable from the refs, possibly accompa-
nied by meta data from one or more porcelains. A repository can
share an object database with other repositories via alternates
mechanism.
resolve
The action of fixing up manually what a failed automatic merge
left behind.
revision
A particular state of files and directories which was stored in
the object database. It is referenced by a commit object.
rewind To throw away part of the development, i.e. to assign the head
to an earlier revision.
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SCM Source code management (tool).
SHA1 Synonym for object name.
shallow repository
A shallow repository has an incomplete history some of whose
commits have parents cauterized away (in other words, git is
told to pretend that these commits do not have the parents, even
though they are recorded in the commit object). This is some-
times useful when you are interested only in the recent history
of a project even though the real history recorded in the
upstream is much larger. A shallow repository is created by giv-
ing the --depth option to git-clone(1), and its history can be
later deepened with git-fetch(1).
symref Symbolic reference: instead of containing the SHA1 id itself, it
is of the format ref: refs/some/thing and when referenced, it
recursively dereferences to this reference. HEAD is a prime
example of a symref. Symbolic references are manipulated with
the git-symbolic-ref(1) command.
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 would be called an object type in git’s
context). A tag is most typically used to mark a particular
point in the commit ancestry chain.
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".
topic branch
A regular git branch that is used by a developer to identify a
conceptual line of development. Since branches are very easy and
inexpensive, it is often desirable to have several small
branches that each contain very well defined concepts or small
incremental yet related changes.
tracking branch
A regular git branch that is used to follow changes from another
repository. A tracking branch should not contain direct modifi-
cations or have local commits made to it. A tracking branch can
usually be identified as the right-hand-side ref in a Pull: ref-
spec.
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tree Either a working tree, or a tree object together with the depen-
dent blob and tree objects (i.e. a stored representation of a
working tree).
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-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.
unmerged index
An index which contains unmerged index entries.
unreachable object
An object which is not reachable from a branch, tag, or any
other reference.
upstream branch
The default branch that is merged into the branch in question
(or the branch in question is rebased onto). It is configured
via branch.<name>.remote and branch.<name>.merge. If the
upstream branch of A is origin/B sometimes we say "A is tracking
origin/B".
working tree
The tree of actual checked out files. The working tree normally
contains the contents of the HEAD commit’s tree, plus any
local changes that you have made but not yet committed.
SEE ALSOgittutorial(7), gittutorial-2(7), gitcvs-migration(7), Everyday git:
everyday.html, The Git User’s Manual: user-manual.html
GIT
Part of the git(1) suite.
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