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NAME
gitglossary - 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
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.
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 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.
cache
Obsolete for: index.
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).
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.
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 commit.
clean
A working tree is clean, if it corresponds to the revision referenced 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 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 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.
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 from any reference or object in the
repository.
detached HEAD
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
"detached".
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.
directory
The list you get with "ls" :-)
dirty
A working tree is said to be "dirty" if it contains modifications which have not been
committed to the current branch.
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 revision 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 mergecommit but instead just update to his
revision. This will happen frequently on a remote-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.
Git archive
Synonym for repository (for arch people).
gitfile
A plain file .git at the root of a working tree that points at the directory that is
the real repository.
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 for object name.
head
A named reference to the commit at the tip of a branch. Heads are stored in a file in
$GIT_DIR/refs/heads/ directory, except when using packed refs. (See git-pack-refs(1).)
HEAD
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.
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 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.
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).
master
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.
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
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 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 SHA-1 of its contents.
Consequently, an object can not be changed.
object database
Stores a set of "objects", and an individual object is identified 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 object name is usually represented by a 40
character hexadecimal string. Also colloquially called SHA-1.
object type
One of the identifiers "commit", "tree", "tag" or "blob" describing the type of an
object.
octopus
To merge more than two branches.
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.
pathspec
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 worktree. See the documentation of each
command for whether paths are relative to the current directory or toplevel. The
pathspec syntax is as follows:
• 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 charaters 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 a 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.
top
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.
literal
Wildcards in the pattern such as * or ? are treated as literal characters.
icase
Case insensitive match.
glob
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 "tools/perf/Documentation/perf.html".
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 "foo".
• 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 invalid.
Glob magic is incompatible with literal magic.
exclude
After a path matches any non-exclude pathspec, it will be run through all exclude
pathspec (magic signature: !). If it matches, the path is ignored.
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 "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.
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 name that begins with refs/ (e.g. refs/heads/master) 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
gitrevisions(7) 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.
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.
remote-tracking branch
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 it.
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 via
alternates mechanism.
resolve
The action of fixing up manually what a failed automatic merge left behind.
revision
Synonym for commit (the noun).
rewind
To throw away part of the development, i.e. to assign the head to an earlier revision.
SCM
Source code management (tool).
SHA-1
"Secure Hash Algorithm 1"; a cryptographic hash function. In the context of Git used
as a 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 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).
symref
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 git-symbolic-ref(1) command.
tag
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.
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.
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).
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 (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, etc.
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 ALSO
gittutorial(7), gittutorial-2(7), gitcvs-migration(7), Everyday Git[1], The Git User’s
Manual[2]
GIT
Part of the git(1) suite.
NOTES
1. Everyday Git
file:///usr/share/doc/git/html/everyday.html
2. The Git User’s Manual
file:///usr/share/doc/git/html/user-manual.html