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.
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. 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 modifications
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 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 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.
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 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 may reference 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 SHA1
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 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.
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 "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 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/master: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 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
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.
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 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 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
modifications or have local commits made to it. A tracking branch
can usually be identified as the right-hand-side ref in a Pull:
refspec.
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-doc/everyday.html
2. The Git User's Manual
file:///usr/share/doc/git-doc/user-manual.html