alternate object database
Via the alternates mechanism, a repository can inherit
part of its object database from another object database, which is called an
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 present 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 repositories make bare repositories available.
Untyped object, e.g. the contents of a file.
A "branch" is a 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 single 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.
Obsolete for: index.
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).
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.
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.
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 commit.
A working tree is clean, if it corresponds to the
revision referenced by the current head. Also see "dirty".
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
project’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 graph concept, representations and usage
A synonym for the DAG structure formed by the commits in
the object database, referenced by branch tips, using their chain of linked
commits. This structure is the definitive commit graph. The graph can be
represented in other ways, e.g. the "commit-graph" file.
The "commit-graph" (normally hyphenated) file
is a supplemental representation of the commit graph which accelerates commit
graph walks. The "commit-graph" file is stored either in the
.git/objects/info directory or in the info directory of an alternate 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.
commit-ish (also committish)
A commit object or an object that can be recursively
dereferenced to a commit object. The following are all commit-ishes: a commit
object, a tag object that points to a commit object, a tag object that points
to a tag object that points to a commit object, etc.
Fundamental data structures and utilities of Git. Exposes
only limited source code management tools.
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
An unreachable object which is not reachable even from
other unreachable objects; a dangling object has no references to it from any
reference or object in the repository.
Normally the HEAD stores the name of a branch, and
commands that operate on the history HEAD represents operate on the history
leading to the tip of the branch the HEAD points at. However, Git also allows
you to check out an arbitrary commit that isn’t necessarily the tip of
any particular branch. The HEAD in such a state is called
Note that commands that operate on the history of the current
branch (e.g. git commit to build a new history on top of it) still
work while the HEAD is detached. They update the HEAD to point at the tip of
the updated history without affecting any branch. Commands that update or
inquire information about the current branch (e.g. git branch
--set-upstream-to that sets what remote-tracking branch the current
branch integrates with) obviously do not work, as there is no (real) current
branch to ask about in this state.
The list you get with "ls" :-)
A working tree is said to be "dirty" if it
contains modifications which have not been committed to the current
An evil merge is a merge that introduces changes that do
not appear in any parent.
A fast-forward is a special type of merge where you have
a revision and you are "merging" another branch's changes that
happen to be a descendant of what you have. In such a case, you do not make a
new merge commit but instead just update your branch to point at the same
revision as the branch you are merging. This will happen frequently on a
remote-tracking branch of a remote repository.
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
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.
Synonym for repository (for arch people).
A plain file .git at the root of a working tree
that points at the directory that is the real repository.
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
Note that the grafts mechanism is outdated and can lead to
problems transferring objects between repositories; see
git-replace(1) for a more flexible and robust system to do the same
In Git’s context, synonym for object name.
A named reference to the commit at the tip of a branch.
Heads are stored in a file in $GIT_DIR/refs/heads/
when using packed refs. (See git-pack-refs(1)
The current branch. In more detail: Your working tree is
normally 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 directly references an arbitrary commit.
A synonym for head.
During the normal execution of several Git commands,
call-outs are made to optional scripts that allow a developer to add
functionality 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.
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.
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).
The default development branch. Whenever you create a Git
repository, a branch named "master" is created, and becomes the
active branch. In most cases, this contains the local development, though that
is purely by convention and is not required.
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 merging the result into the current
branch. This combination of fetch and merge operations is called a pull.
Merging is performed 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
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".
The unit of storage in Git. It is uniquely identified by
the SHA-1 of its contents. Consequently, an object cannot be changed.
Stores a set of "objects", and an individual
object is identified by its object name. The objects usually live in
object identifier (oid)
Synonym for object name.
The unique identifier of an object. The object name is
usually represented by a 40 character hexadecimal string. Also colloquially
One of the identifiers "commit",
"tree", "tag" or "blob" describing the type of
To merge more than two branches.
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
Only update and add files to the working directory, but
don’t delete them, similar to how cp -R would update the
contents in the destination directory. This is the default mode in a checkout
when checking out files from the index or a tree-ish. In contrast, no-overlay
mode also deletes tracked files not present in the source, similar to rsync
A set of objects which have been compressed into one file
(to save space or to transmit them efficiently).
The list of identifiers, and other information, of the
objects in a pack, to assist in efficiently accessing the contents of a
Pattern used to limit paths in Git commands.
Pathspecs are used on the command line of "git
ls-files", "git ls-tree", "git add", "git
grep", "git diff", "git checkout", and many other
commands to limit the scope of operations to some subset of the tree or
working tree. See the documentation of each command for whether paths are
relative to the current directory or toplevel. The pathspec syntax is as
•any path matches itself
•the pathspec up to the last slash represents a
directory prefix. The scope of that pathspec is limited to that subtree.
•the rest of the pathspec is a pattern for the
remainder of the pathname. Paths relative to the directory prefix will be
matched against that pattern using fnmatch(3); in particular, * and
? can match directory separators.
For example, Documentation/*.jpg will match all .jpg files in the
Documentation subtree, including Documentation/chapter_1/figure_1.jpg.
A pathspec that begins with a colon : has special meaning.
In the short form, the leading colon : is followed by zero or more
"magic signature" letters (which optionally is terminated by
another colon :), and the remainder is the pattern to match against
the path. The "magic signature" consists of ASCII symbols that are
neither alphanumeric, glob, regex special characters nor colon. The optional
colon that terminates the "magic signature" can be omitted if the
pattern begins with a character that does not belong to "magic
signature" symbol set and is not a colon.
In the long form, the leading colon : is followed by an
open parenthesis (, a comma-separated list of zero or more
"magic words", and a close parentheses ), and the remainder
is the pattern to match against the path.
A pathspec with only a colon means "there is no
pathspec". This form should not be combined with other pathspec.
The magic word top (magic signature: /)
makes the pattern match from the root of the working tree, even when you are
running the command from inside a subdirectory.
Wildcards in the pattern such as * or ? are
treated as literal characters.
Case insensitive match.
Git treats the pattern as a shell glob suitable for
consumption by fnmatch(3) with the FNM_PATHNAME flag: wildcards in the pattern
will not match a / in the pathname. For example,
"Documentation/*.html" matches "Documentation/git.html"
but not "Documentation/ppc/ppc.html" or
Two consecutive asterisks ("**") in patterns
matched against full pathname may have special meaning:
•A leading "**" followed by a
slash means match in all directories. For example, "**/foo"
matches file or directory "foo" anywhere, the same as pattern
"foo". "**/foo/bar" matches file or
directory "bar" anywhere that is directly under directory
•A trailing "/**" matches
everything inside. For example, "abc/**" matches all files
inside directory "abc", relative to the location of the
.gitignore file, with infinite depth.
•A slash followed by two consecutive asterisks
then a slash matches zero or more directories. For example,
"a/**/b" matches "a/b",
"a/x/b", "a/x/y/b" and so on.
•Other consecutive asterisks are considered
Glob magic is incompatible with literal magic.
comes a space separated list of
"attribute requirements", all of which must be met in order for the
path to be considered a match; this is in addition to the usual non-magic
pathspec pattern matching. See gitattributes(5)
Each of the attribute requirements for the path takes one of these
•"ATTR" requires that the
attribute ATTR be set.
•"-ATTR" requires that the
attribute ATTR be unset.
•"ATTR=VALUE" requires that the
attribute ATTR be set to the string VALUE.
" requires that the
Note that when matching against a tree object, attributes are
still obtained from working tree, not from the given tree object.
After a path matches any non-exclude pathspec, it will be
run through all exclude pathspecs (magic signature: ! or its synonym
^). If it matches, the path is ignored. When there is no non-exclude
pathspec, the exclusion is applied to the result set as if invoked without any
A commit object contains a (possibly empty) list of the
logical predecessor(s) in the line of development, i.e. its parents.
The term pickaxe refers to an option to the diffcore
routines that help select changes that add or delete a given text string. With
option, it can be used to view the full changeset
that introduced or removed, say, a particular line of text. See
Cute name for core Git.
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.
Refs that are per-worktree, rather than global. This is
presently only HEAD and any refs that start with refs/bisect/, but
might later include other unusual refs.
Pseudorefs are a class of files under $GIT_DIR
which behave like refs for the purposes of rev-parse, but which are treated
specially by git. Pseudorefs both have names that are all-caps, and always
start with a line consisting of a SHA-1 followed by whitespace. So, HEAD is
not a pseudoref, because it is sometimes a symbolic ref. They might optionally
contain some additional data. MERGE_HEAD and CHERRY_PICK_HEAD
are examples. Unlike per-worktree refs, these files cannot be symbolic refs,
and never have reflogs. They also cannot be updated through the normal ref
update machinery. Instead, they are updated by directly writing to the files.
However, they can be read as if they were refs, so git rev-parse
MERGE_HEAD will work.
Pulling a branch means to fetch it and merge it. See also
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, 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.
All of the ancestors of a given commit are said to be
"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 contain.
Reachability bitmaps store information about the
reachability of a selected set of commits in a packfile, or a multi-pack index
(MIDX), to speed up object search. The bitmaps are stored in a
".bitmap" file. A repository may have at most one bitmap file in
use. The bitmap file may belong to either one pack, or the repository’s
multi-pack index (if it exists).
To reapply a series of changes from a branch to a
different base, and reset the head of that branch to the result.
A name that begins with refs/
) that points to an object name or another ref (the
latter is called a symbolic ref). For convenience, a ref can sometimes be
abbreviated when used as an argument to a Git command; see
for details. Refs are stored in the repository.
The ref namespace is hierarchical. Different subhierarchies are
used for different purposes (e.g. the refs/heads/ hierarchy is used
to represent local branches).
There are a few special-purpose refs that do not begin with
refs/. The most notable example is HEAD.
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
yesterday 9:14pm. See git-reflog(1)
A "refspec" is used by fetch and push to
describe the mapping between remote ref and local ref.
A repository which is used to track the same project but
resides somewhere else. To communicate with remotes, see fetch or push.
A ref that is used to follow changes from another
repository. It typically looks like refs/remotes/foo/bar (indicating
that it tracks a branch named bar in a remote named foo), and
matches the right-hand-side of a configured fetch refspec. A remote-tracking
branch should not contain direct modifications or have local commits made to
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 via alternates mechanism.
The action of fixing up manually what a failed automatic
merge left behind.
Synonym for commit (the noun).
To throw away part of the development, i.e. to assign the
head to an earlier revision.
Source code management (tool).
"Secure Hash Algorithm 1"; a cryptographic hash
function. In the context of Git used as a synonym for object name.
Mostly a synonym to shallow repository but the phrase
makes it more explicit that it was created by running git clone
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 sometimes 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 giving the --depth
option to git-clone(1)
, and its
history can be later deepened with git-fetch(1)
An object used to temporarily store the contents of a
dirty working directory and the index for future reuse.
A repository that holds the history of a separate project
inside another repository (the latter of which is called superproject).
A repository that references repositories of other
projects in its working tree as submodules. The superproject knows about the
names of (but does not hold copies of) commit objects of the contained
Symbolic reference: instead of containing the SHA-1 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
A ref under refs/tags/ namespace that points to an
object of an arbitrary type (typically a tag points to either a tag or a
commit object). In contrast to a head, a tag is not updated by the
commit command. 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.
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
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
Either a working tree, or a tree object together with the
dependent blob and tree objects (i.e. a stored representation of a working
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
tree-ish (also treeish)
A tree object or an object that can be recursively
dereferenced to a tree object. Dereferencing a commit object yields the tree
object corresponding to the revision's top directory. The following are all
tree-ishes: a commit-ish, a tree object, a tag object that points to a tree
object, a tag object that points to a tag object that points to a tree object,
An index which contains unmerged index entries.
An object which is not reachable from a branch, tag, or
any other reference.
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
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.
A repository can have zero (i.e. bare repository) or one
or more worktrees attached to it. One "worktree" consists of a
"working tree" and repository metadata, most of which are shared
among other worktrees of a single repository, and some of which are maintained
separately per worktree (e.g. the index, HEAD and pseudorefs like MERGE_HEAD,
per-worktree refs and per-worktree configuration file).