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1 GIT Glossary
2 ============
4 [[def_alternate_object_database]]alternate object database::
5 Via the alternates mechanism, a <<def_repository,repository>>
6 can inherit part of its <<def_object_database,object database>>
7 from another object database, which is called "alternate".
9 [[def_bare_repository]]bare repository::
10 A bare repository is normally an appropriately
11 named <<def_directory,directory>> with a `.git` suffix that does not
12 have a locally checked-out copy of any of the files under
13 revision control. That is, all of the `git`
14 administrative and control files that would normally be present in the
15 hidden `.git` sub-directory are directly present in the
16 `repository.git` directory instead,
17 and no other files are present and checked out. Usually publishers of
18 public repositories make bare repositories available.
20 [[def_blob_object]]blob object::
21 Untyped <<def_object,object>>, e.g. the contents of a file.
23 [[def_branch]]branch::
24 A "branch" is an active line of development. The most recent
25 <<def_commit,commit>> on a branch is referred to as the tip of
26 that branch. The tip of the branch is referenced by a branch
27 <<def_head,head>>, which moves forward as additional development
28 is done on the branch. A single git
29 <<def_repository,repository>> can track an arbitrary number of
30 branches, but your <<def_working_tree,working tree>> is
31 associated with just one of them (the "current" or "checked out"
32 branch), and <<def_HEAD,HEAD>> points to that branch.
34 [[def_cache]]cache::
35 Obsolete for: <<def_index,index>>.
37 [[def_chain]]chain::
38 A list of objects, where each <<def_object,object>> in the list contains
39 a reference to its successor (for example, the successor of a
40 <<def_commit,commit>> could be one of its <<def_parent,parents>>).
42 [[def_changeset]]changeset::
43 BitKeeper/cvsps speak for "<<def_commit,commit>>". Since git does not
44 store changes, but states, it really does not make sense to use the term
45 "changesets" with git.
47 [[def_checkout]]checkout::
48 The action of updating the <<def_working_tree,working tree>> to a
49 <<def_revision,revision>> which was stored in the
50 <<def_object_database,object database>>.
52 [[def_cherry-picking]]cherry-picking::
53 In <<def_SCM,SCM>> jargon, "cherry pick" means to choose a subset of
54 changes out of a series of changes (typically commits) and record them
55 as a new series of changes on top of a different codebase. In GIT, this is
56 performed by the "git cherry-pick" command to extract the change introduced
57 by an existing <<def_commit,commit>> and to record it based on the tip
58 of the current <<def_branch,branch>> as a new commit.
60 [[def_clean]]clean::
61 A <<def_working_tree,working tree>> is clean, if it
62 corresponds to the <<def_revision,revision>> referenced by the current
63 <<def_head,head>>. Also see "<<def_dirty,dirty>>".
65 [[def_commit]]commit::
66 As a noun: A single point in the
67 git history; the entire history of a project is represented as a
68 set of interrelated commits. The word "commit" is often
69 used by git in the same places other revision control systems
70 use the words "revision" or "version". Also used as a short
71 hand for <<def_commit_object,commit object>>.
72 +
73 As a verb: The action of storing a new snapshot of the project's
74 state in the git history, by creating a new commit representing the current
75 state of the <<def_index,index>> and advancing <<def_HEAD,HEAD>>
76 to point at the new commit.
78 [[def_commit_object]]commit object::
79 An <<def_object,object>> which contains the information about a
80 particular <<def_revision,revision>>, such as <<def_parent,parents>>, committer,
81 author, date and the <<def_tree_object,tree object>> which corresponds
82 to the top <<def_directory,directory>> of the stored
83 revision.
85 [[def_core_git]]core git::
86 Fundamental data structures and utilities of git. Exposes only limited
87 source code management tools.
89 [[def_DAG]]DAG::
90 Directed acyclic graph. The <<def_commit,commit>> objects form a
91 directed acyclic graph, because they have parents (directed), and the
92 graph of commit objects is acyclic (there is no
93 <<def_chain,chain>> which begins and ends with the same
94 <<def_object,object>>).
96 [[def_dangling_object]]dangling object::
97 An <<def_unreachable_object,unreachable object>> which is not
98 <<def_reachable,reachable>> even from other unreachable objects; a
99 dangling object has no references to it from any
100 reference or <<def_object,object>> in the <<def_repository,repository>>.
102 [[def_detached_HEAD]]detached HEAD::
103 Normally the <<def_HEAD,HEAD>> stores the name of a
104 <<def_branch,branch>>. However, git also allows you to <<def_checkout,check out>>
105 an arbitrary <<def_commit,commit>> that isn't necessarily the tip of any
106 particular branch. In this case HEAD is said to be "detached".
108 [[def_dircache]]dircache::
109 You are *waaaaay* behind. See <<def_index,index>>.
111 [[def_directory]]directory::
112 The list you get with "ls" :-)
114 [[def_dirty]]dirty::
115 A <<def_working_tree,working tree>> is said to be "dirty" if
116 it contains modifications which have not been <<def_commit,committed>> to the current
117 <<def_branch,branch>>.
119 [[def_ent]]ent::
120 Favorite synonym to "<<def_tree-ish,tree-ish>>" by some total geeks. See
121 `http://en.wikipedia.org/wiki/Ent_(Middle-earth)` for an in-depth
122 explanation. Avoid this term, not to confuse people.
124 [[def_evil_merge]]evil merge::
125 An evil merge is a <<def_merge,merge>> that introduces changes that
126 do not appear in any <<def_parent,parent>>.
128 [[def_fast_forward]]fast forward::
129 A fast-forward is a special type of <<def_merge,merge>> where you have a
130 <<def_revision,revision>> and you are "merging" another
131 <<def_branch,branch>>'s changes that happen to be a descendant of what
132 you have. In such these cases, you do not make a new <<def_merge,merge>>
133 <<def_commit,commit>> but instead just update to his
134 revision. This will happen frequently on a
135 <<def_tracking_branch,tracking branch>> of a remote
136 <<def_repository,repository>>.
138 [[def_fetch]]fetch::
139 Fetching a <<def_branch,branch>> means to get the
140 branch's <<def_head_ref,head ref>> from a remote
141 <<def_repository,repository>>, to find out which objects are
142 missing from the local <<def_object_database,object database>>,
143 and to get them, too. See also gitlink:git-fetch[1].
145 [[def_file_system]]file system::
146 Linus Torvalds originally designed git to be a user space file system,
147 i.e. the infrastructure to hold files and directories. That ensured the
148 efficiency and speed of git.
150 [[def_git_archive]]git archive::
151 Synonym for <<def_repository,repository>> (for arch people).
153 [[def_grafts]]grafts::
154 Grafts enables two otherwise different lines of development to be joined
155 together by recording fake ancestry information for commits. This way
156 you can make git pretend the set of <<def_parent,parents>> a <<def_commit,commit>> has
157 is different from what was recorded when the commit was
158 created. Configured via the `.git/info/grafts` file.
160 [[def_hash]]hash::
161 In git's context, synonym to <<def_object_name,object name>>.
163 [[def_head]]head::
164 A <<def_ref,named reference>> to the <<def_commit,commit>> at the tip of a
165 <<def_branch,branch>>. Heads are stored in
166 `$GIT_DIR/refs/heads/`, except when using packed refs. (See
167 gitlink:git-pack-refs[1].)
169 [[def_HEAD]]HEAD::
170 The current <<def_branch,branch>>. In more detail: Your <<def_working_tree,
171 working tree>> is normally derived from the state of the tree
172 referred to by HEAD. HEAD is a reference to one of the
173 <<def_head,heads>> in your repository, except when using a
174 <<def_detached_HEAD,detached HEAD>>, in which case it may
175 reference an arbitrary commit.
177 [[def_head_ref]]head ref::
178 A synonym for <<def_head,head>>.
180 [[def_hook]]hook::
181 During the normal execution of several git commands, call-outs are made
182 to optional scripts that allow a developer to add functionality or
183 checking. Typically, the hooks allow for a command to be pre-verified
184 and potentially aborted, and allow for a post-notification after the
185 operation is done. The hook scripts are found in the
186 `$GIT_DIR/hooks/` directory, and are enabled by simply
187 making them executable.
189 [[def_index]]index::
190 A collection of files with stat information, whose contents are stored
191 as objects. The index is a stored version of your
192 <<def_working_tree,working tree>>. Truth be told, it can also contain a second, and even
193 a third version of a working tree, which are used
194 when <<def_merge,merging>>.
196 [[def_index_entry]]index entry::
197 The information regarding a particular file, stored in the
198 <<def_index,index>>. An index entry can be unmerged, if a
199 <<def_merge,merge>> was started, but not yet finished (i.e. if
200 the index contains multiple versions of that file).
202 [[def_master]]master::
203 The default development <<def_branch,branch>>. Whenever you
204 create a git <<def_repository,repository>>, a branch named
205 "master" is created, and becomes the active branch. In most
206 cases, this contains the local development, though that is
207 purely by convention and is not required.
209 [[def_merge]]merge::
210 As a verb: To bring the contents of another
211 <<def_branch,branch>> (possibly from an external
212 <<def_repository,repository>>) into the current branch. In the
213 case where the merged-in branch is from a different repository,
214 this is done by first <<def_fetch,fetching>> the remote branch
215 and then merging the result into the current branch. This
216 combination of fetch and merge operations is called a
217 <<def_pull,pull>>. Merging is performed by an automatic process
218 that identifies changes made since the branches diverged, and
219 then applies all those changes together. In cases where changes
220 conflict, manual intervention may be required to complete the
221 merge.
222 +
223 As a noun: unless it is a <<def_fast_forward,fast forward>>, a
224 successful merge results in the creation of a new <<def_commit,commit>>
225 representing the result of the merge, and having as
226 <<def_parent,parents>> the tips of the merged <<def_branch,branches>>.
227 This commit is referred to as a "merge commit", or sometimes just a
228 "merge".
230 [[def_object]]object::
231 The unit of storage in git. It is uniquely identified by the
232 <<def_SHA1,SHA1>> of its contents. Consequently, an
233 object can not be changed.
235 [[def_object_database]]object database::
236 Stores a set of "objects", and an individual <<def_object,object>> is
237 identified by its <<def_object_name,object name>>. The objects usually
238 live in `$GIT_DIR/objects/`.
240 [[def_object_identifier]]object identifier::
241 Synonym for <<def_object_name,object name>>.
243 [[def_object_name]]object name::
244 The unique identifier of an <<def_object,object>>. The <<def_hash,hash>>
245 of the object's contents using the Secure Hash Algorithm
246 1 and usually represented by the 40 character hexadecimal encoding of
247 the <<def_hash,hash>> of the object (possibly followed by
248 a white space).
250 [[def_object_type]]object type::
251 One of the identifiers
252 "<<def_commit,commit>>","<<def_tree,tree>>","<<def_tag,tag>>" or "<<def_blob_object,blob>>"
253 describing the type of an <<def_object,object>>.
255 [[def_octopus]]octopus::
256 To <<def_merge,merge>> more than two <<def_branch,branches>>. Also denotes an
257 intelligent predator.
259 [[def_origin]]origin::
260 The default upstream <<def_repository,repository>>. Most projects have
261 at least one upstream project which they track. By default
262 'origin' is used for that purpose. New upstream updates
263 will be fetched into remote <<def_tracking_branch,tracking branches>> named
264 origin/name-of-upstream-branch, which you can see using
265 "`git branch -r`".
267 [[def_pack]]pack::
268 A set of objects which have been compressed into one file (to save space
269 or to transmit them efficiently).
271 [[def_pack_index]]pack index::
272 The list of identifiers, and other information, of the objects in a
273 <<def_pack,pack>>, to assist in efficiently accessing the contents of a
274 pack.
276 [[def_parent]]parent::
277 A <<def_commit_object,commit object>> contains a (possibly empty) list
278 of the logical predecessor(s) in the line of development, i.e. its
279 parents.
281 [[def_pickaxe]]pickaxe::
282 The term <<def_pickaxe,pickaxe>> refers to an option to the diffcore
283 routines that help select changes that add or delete a given text
284 string. With the --pickaxe-all option, it can be used to view the full
285 <<def_changeset,changeset>> that introduced or removed, say, a
286 particular line of text. See gitlink:git-diff[1].
288 [[def_plumbing]]plumbing::
289 Cute name for <<def_core_git,core git>>.
291 [[def_porcelain]]porcelain::
292 Cute name for programs and program suites depending on
293 <<def_core_git,core git>>, presenting a high level access to
294 core git. Porcelains expose more of a <<def_SCM,SCM>>
295 interface than the <<def_plumbing,plumbing>>.
297 [[def_pull]]pull::
298 Pulling a <<def_branch,branch>> means to <<def_fetch,fetch>> it and
299 <<def_merge,merge>> it. See also gitlink:git-pull[1].
301 [[def_push]]push::
302 Pushing a <<def_branch,branch>> means to get the branch's
303 <<def_head_ref,head ref>> from a remote <<def_repository,repository>>,
304 find out if it is an ancestor to the branch's local
305 head ref is a direct, and in that case, putting all
306 objects, which are <<def_reachable,reachable>> from the local
307 head ref, and which are missing from the remote
308 repository, into the remote
309 <<def_object_database,object database>>, and updating the remote
310 head ref. If the remote <<def_head,head>> is not an
311 ancestor to the local head, the push fails.
313 [[def_reachable]]reachable::
314 All of the ancestors of a given <<def_commit,commit>> are said to be
315 "reachable" from that commit. More
316 generally, one <<def_object,object>> is reachable from
317 another if we can reach the one from the other by a <<def_chain,chain>>
318 that follows <<def_tag,tags>> to whatever they tag,
319 <<def_commit_object,commits>> to their parents or trees, and
320 <<def_tree_object,trees>> to the trees or <<def_blob_object,blobs>>
321 that they contain.
323 [[def_rebase]]rebase::
324 To reapply a series of changes from a <<def_branch,branch>> to a
325 different base, and reset the <<def_head,head>> of that branch
326 to the result.
328 [[def_ref]]ref::
329 A 40-byte hex representation of a <<def_SHA1,SHA1>> or a name that
330 denotes a particular <<def_object,object>>. These may be stored in
331 `$GIT_DIR/refs/`.
333 [[def_reflog]]reflog::
334 A reflog shows the local "history" of a ref. In other words,
335 it can tell you what the 3rd last revision in _this_ repository
336 was, and what was the current state in _this_ repository,
337 yesterday 9:14pm. See gitlink:git-reflog[1] for details.
339 [[def_refspec]]refspec::
340 A "refspec" is used by <<def_fetch,fetch>> and
341 <<def_push,push>> to describe the mapping between remote
342 <<def_ref,ref>> and local ref. They are combined with a colon in
343 the format <src>:<dst>, preceded by an optional plus sign, +.
344 For example: `git fetch $URL
345 refs/heads/master:refs/heads/origin` means "grab the master
346 <<def_branch,branch>> <<def_head,head>> from the $URL and store
347 it as my origin branch head". And `git push
348 $URL refs/heads/master:refs/heads/to-upstream` means "publish my
349 master branch head as to-upstream branch at $URL". See also
350 gitlink:git-push[1].
352 [[def_repository]]repository::
353 A collection of <<def_ref,refs>> together with an
354 <<def_object_database,object database>> containing all objects
355 which are <<def_reachable,reachable>> from the refs, possibly
356 accompanied by meta data from one or more <<def_porcelain,porcelains>>. A
357 repository can share an object database with other repositories
358 via <<def_alternate_object_database,alternates mechanism>>.
360 [[def_resolve]]resolve::
361 The action of fixing up manually what a failed automatic
362 <<def_merge,merge>> left behind.
364 [[def_revision]]revision::
365 A particular state of files and directories which was stored in the
366 <<def_object_database,object database>>. It is referenced by a
367 <<def_commit_object,commit object>>.
369 [[def_rewind]]rewind::
370 To throw away part of the development, i.e. to assign the
371 <<def_head,head>> to an earlier <<def_revision,revision>>.
373 [[def_SCM]]SCM::
374 Source code management (tool).
376 [[def_SHA1]]SHA1::
377 Synonym for <<def_object_name,object name>>.
379 [[def_shallow_repository]]shallow repository::
380 A shallow <<def_repository,repository>> has an incomplete
381 history some of whose <<def_commit,commits>> have <<def_parent,parents>> cauterized away (in other
382 words, git is told to pretend that these commits do not have the
383 parents, even though they are recorded in the <<def_commit_object,commit
384 object>>). This is sometimes useful when you are interested only in the
385 recent history of a project even though the real history recorded in the
386 upstream is much larger. A shallow repository
387 is created by giving the `--depth` option to gitlink:git-clone[1], and
388 its history can be later deepened with gitlink:git-fetch[1].
390 [[def_symref]]symref::
391 Symbolic reference: instead of containing the <<def_SHA1,SHA1>>
392 id itself, it is of the format 'ref: refs/some/thing' and when
393 referenced, it recursively dereferences to this reference.
394 '<<def_HEAD,HEAD>>' is a prime example of a symref. Symbolic
395 references are manipulated with the gitlink:git-symbolic-ref[1]
396 command.
398 [[def_tag]]tag::
399 A <<def_ref,ref>> pointing to a <<def_tag_object,tag>> or
400 <<def_commit_object,commit object>>. In contrast to a <<def_head,head>>,
401 a tag is not changed by a <<def_commit,commit>>. Tags (not
402 <<def_tag_object,tag objects>>) are stored in `$GIT_DIR/refs/tags/`. A
403 git tag has nothing to do with a Lisp tag (which would be
404 called an <<def_object_type,object type>> in git's context). A
405 tag is most typically used to mark a particular point in the
406 commit ancestry <<def_chain,chain>>.
408 [[def_tag_object]]tag object::
409 An <<def_object,object>> containing a <<def_ref,ref>> pointing to
410 another object, which can contain a message just like a
411 <<def_commit_object,commit object>>. It can also contain a (PGP)
412 signature, in which case it is called a "signed tag object".
414 [[def_topic_branch]]topic branch::
415 A regular git <<def_branch,branch>> that is used by a developer to
416 identify a conceptual line of development. Since branches are very easy
417 and inexpensive, it is often desirable to have several small branches
418 that each contain very well defined concepts or small incremental yet
419 related changes.
421 [[def_tracking_branch]]tracking branch::
422 A regular git <<def_branch,branch>> that is used to follow changes from
423 another <<def_repository,repository>>. A tracking
424 branch should not contain direct modifications or have local commits
425 made to it. A tracking branch can usually be
426 identified as the right-hand-side <<def_ref,ref>> in a Pull:
427 <<def_refspec,refspec>>.
429 [[def_tree]]tree::
430 Either a <<def_working_tree,working tree>>, or a <<def_tree_object,tree
431 object>> together with the dependent <<def_blob_object,blob>> and tree objects
432 (i.e. a stored representation of a working tree).
434 [[def_tree_object]]tree object::
435 An <<def_object,object>> containing a list of file names and modes along
436 with refs to the associated blob and/or tree objects. A
437 <<def_tree,tree>> is equivalent to a <<def_directory,directory>>.
439 [[def_tree-ish]]tree-ish::
440 A <<def_ref,ref>> pointing to either a <<def_commit_object,commit
441 object>>, a <<def_tree_object,tree object>>, or a <<def_tag_object,tag
442 object>> pointing to a tag or commit or tree object.
444 [[def_unmerged_index]]unmerged index::
445 An <<def_index,index>> which contains unmerged
446 <<def_index_entry,index entries>>.
448 [[def_unreachable_object]]unreachable object::
449 An <<def_object,object>> which is not <<def_reachable,reachable>> from a
450 <<def_branch,branch>>, <<def_tag,tag>>, or any other reference.
452 [[def_working_tree]]working tree::
453 The tree of actual checked out files. The working tree is
454 normally equal to the <<def_HEAD,HEAD>> plus any local changes
455 that you have made but not yet committed.