GITGLOSSARY(7) Git Manual GITGLOSSARY(7)
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
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
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.
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 optional colon that terminates the "magic
signature" can be omitted if the pattern begins with a character that cannot be a "magic signature" 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.
The "magic signature" consists of an ASCII symbol that is not alphanumeric. Currently only the slash / is
recognized as a "magic signature": it makes the pattern match from the root of the working tree, even when
you are running the command from inside a subdirectory.
A pathspec with only a colon means "there is no pathspec". This form should not be combined with other
pathspec.
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.
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 40-byte hex representation of a SHA-1 or a name that denotes a particular object. They may be stored in
a file under $GIT_DIR/refs/ directory, or in the $GIT_DIR/packed-refs file.
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 regular Git branch that is used to follow changes from another repository. A remote-tracking branch
should not contain direct modifications or have local commits made to it. A remote-tracking branch can
usually be identified as the right-hand-side ref in a Pull: refspec.
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
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
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 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-1.8.3.1/everyday.html
2. The Git User’s Manual
file:///usr/share/doc/git-1.8.3.1/user-manual.html
Git 1.8.3.1 03/23/2016 GITGLOSSARY(7)
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