db2a74df934f3acd93521e42510b6cd00c9eed6f
[git/git.git] / Documentation / glossary-content.txt
1 [[def_alternate_object_database]]alternate object database::
2 Via the alternates mechanism, a <<def_repository,repository>>
3 can inherit part of its <<def_object_database,object database>>
4 from another object database, which is called "alternate".
5
6 [[def_bare_repository]]bare repository::
7 A bare repository is normally an appropriately
8 named <<def_directory,directory>> with a `.git` suffix that does not
9 have a locally checked-out copy of any of the files under
10 revision control. That is, all of the Git
11 administrative and control files that would normally be present in the
12 hidden `.git` sub-directory are directly present in the
13 `repository.git` directory instead,
14 and no other files are present and checked out. Usually publishers of
15 public repositories make bare repositories available.
16
17 [[def_blob_object]]blob object::
18 Untyped <<def_object,object>>, e.g. the contents of a file.
19
20 [[def_branch]]branch::
21 A "branch" is an active line of development. The most recent
22 <<def_commit,commit>> on a branch is referred to as the tip of
23 that branch. The tip of the branch is referenced by a branch
24 <<def_head,head>>, which moves forward as additional development
25 is done on the branch. A single Git
26 <<def_repository,repository>> can track an arbitrary number of
27 branches, but your <<def_working_tree,working tree>> is
28 associated with just one of them (the "current" or "checked out"
29 branch), and <<def_HEAD,HEAD>> points to that branch.
30
31 [[def_cache]]cache::
32 Obsolete for: <<def_index,index>>.
33
34 [[def_chain]]chain::
35 A list of objects, where each <<def_object,object>> in the list contains
36 a reference to its successor (for example, the successor of a
37 <<def_commit,commit>> could be one of its <<def_parent,parents>>).
38
39 [[def_changeset]]changeset::
40 BitKeeper/cvsps speak for "<<def_commit,commit>>". Since Git does not
41 store changes, but states, it really does not make sense to use the term
42 "changesets" with Git.
43
44 [[def_checkout]]checkout::
45 The action of updating all or part of the
46 <<def_working_tree,working tree>> with a <<def_tree_object,tree object>>
47 or <<def_blob_object,blob>> from the
48 <<def_object_database,object database>>, and updating the
49 <<def_index,index>> and <<def_HEAD,HEAD>> if the whole working tree has
50 been pointed at a new <<def_branch,branch>>.
51
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.
59
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>>".
64
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.
77
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.
84
85 [[def_core_git]]core Git::
86 Fundamental data structures and utilities of Git. Exposes only limited
87 source code management tools.
88
89 [[def_DAG]]DAG::
90 Directed acyclic graph. The <<def_commit_object,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 <<def_chain,chain>>
93 which begins and ends with the same <<def_object,object>>).
94
95 [[def_dangling_object]]dangling object::
96 An <<def_unreachable_object,unreachable object>> which is not
97 <<def_reachable,reachable>> even from other unreachable objects; a
98 dangling object has no references to it from any
99 reference or <<def_object,object>> in the <<def_repository,repository>>.
100
101 [[def_detached_HEAD]]detached HEAD::
102 Normally the <<def_HEAD,HEAD>> stores the name of a
103 <<def_branch,branch>>, and commands that operate on the
104 history HEAD represents operate on the history leading to the
105 tip of the branch the HEAD points at. However, Git also
106 allows you to <<def_checkout,check out>> an arbitrary
107 <<def_commit,commit>> that isn't necessarily the tip of any
108 particular branch. The HEAD in such a state is called
109 "detached".
110 +
111 Note that commands that operate on the history of the current branch
112 (e.g. `git commit` to build a new history on top of it) still work
113 while the HEAD is detached. They update the HEAD to point at the tip
114 of the updated history without affecting any branch. Commands that
115 update or inquire information _about_ the current branch (e.g. `git
116 branch --set-upstream-to` that sets what remote tracking branch the
117 current branch integrates with) obviously do not work, as there is no
118 (real) current branch to ask about in this state.
119
120 [[def_directory]]directory::
121 The list you get with "ls" :-)
122
123 [[def_dirty]]dirty::
124 A <<def_working_tree,working tree>> is said to be "dirty" if
125 it contains modifications which have not been <<def_commit,committed>> to the current
126 <<def_branch,branch>>.
127
128 [[def_evil_merge]]evil merge::
129 An evil merge is a <<def_merge,merge>> that introduces changes that
130 do not appear in any <<def_parent,parent>>.
131
132 [[def_fast_forward]]fast-forward::
133 A fast-forward is a special type of <<def_merge,merge>> where you have a
134 <<def_revision,revision>> and you are "merging" another
135 <<def_branch,branch>>'s changes that happen to be a descendant of what
136 you have. In such these cases, you do not make a new <<def_merge,merge>>
137 <<def_commit,commit>> but instead just update to his
138 revision. This will happen frequently on a
139 <<def_remote_tracking_branch,remote-tracking branch>> of a remote
140 <<def_repository,repository>>.
141
142 [[def_fetch]]fetch::
143 Fetching a <<def_branch,branch>> means to get the
144 branch's <<def_head_ref,head ref>> from a remote
145 <<def_repository,repository>>, to find out which objects are
146 missing from the local <<def_object_database,object database>>,
147 and to get them, too. See also linkgit:git-fetch[1].
148
149 [[def_file_system]]file system::
150 Linus Torvalds originally designed Git to be a user space file system,
151 i.e. the infrastructure to hold files and directories. That ensured the
152 efficiency and speed of Git.
153
154 [[def_git_archive]]Git archive::
155 Synonym for <<def_repository,repository>> (for arch people).
156
157 [[def_gitfile]]gitfile::
158 A plain file `.git` at the root of a working tree that
159 points at the directory that is the real repository.
160
161 [[def_grafts]]grafts::
162 Grafts enables two otherwise different lines of development to be joined
163 together by recording fake ancestry information for commits. This way
164 you can make Git pretend the set of <<def_parent,parents>> a <<def_commit,commit>> has
165 is different from what was recorded when the commit was
166 created. Configured via the `.git/info/grafts` file.
167
168 [[def_hash]]hash::
169 In Git's context, synonym for <<def_object_name,object name>>.
170
171 [[def_head]]head::
172 A <<def_ref,named reference>> to the <<def_commit,commit>> at the tip of a
173 <<def_branch,branch>>. Heads are stored in a file in
174 `$GIT_DIR/refs/heads/` directory, except when using packed refs. (See
175 linkgit:git-pack-refs[1].)
176
177 [[def_HEAD]]HEAD::
178 The current <<def_branch,branch>>. In more detail: Your <<def_working_tree,
179 working tree>> is normally derived from the state of the tree
180 referred to by HEAD. HEAD is a reference to one of the
181 <<def_head,heads>> in your repository, except when using a
182 <<def_detached_HEAD,detached HEAD>>, in which case it directly
183 references an arbitrary commit.
184
185 [[def_head_ref]]head ref::
186 A synonym for <<def_head,head>>.
187
188 [[def_hook]]hook::
189 During the normal execution of several Git commands, call-outs are made
190 to optional scripts that allow a developer to add functionality or
191 checking. Typically, the hooks allow for a command to be pre-verified
192 and potentially aborted, and allow for a post-notification after the
193 operation is done. The hook scripts are found in the
194 `$GIT_DIR/hooks/` directory, and are enabled by simply
195 removing the `.sample` suffix from the filename. In earlier versions
196 of Git you had to make them executable.
197
198 [[def_index]]index::
199 A collection of files with stat information, whose contents are stored
200 as objects. The index is a stored version of your
201 <<def_working_tree,working tree>>. Truth be told, it can also contain a second, and even
202 a third version of a working tree, which are used
203 when <<def_merge,merging>>.
204
205 [[def_index_entry]]index entry::
206 The information regarding a particular file, stored in the
207 <<def_index,index>>. An index entry can be unmerged, if a
208 <<def_merge,merge>> was started, but not yet finished (i.e. if
209 the index contains multiple versions of that file).
210
211 [[def_master]]master::
212 The default development <<def_branch,branch>>. Whenever you
213 create a Git <<def_repository,repository>>, a branch named
214 "master" is created, and becomes the active branch. In most
215 cases, this contains the local development, though that is
216 purely by convention and is not required.
217
218 [[def_merge]]merge::
219 As a verb: To bring the contents of another
220 <<def_branch,branch>> (possibly from an external
221 <<def_repository,repository>>) into the current branch. In the
222 case where the merged-in branch is from a different repository,
223 this is done by first <<def_fetch,fetching>> the remote branch
224 and then merging the result into the current branch. This
225 combination of fetch and merge operations is called a
226 <<def_pull,pull>>. Merging is performed by an automatic process
227 that identifies changes made since the branches diverged, and
228 then applies all those changes together. In cases where changes
229 conflict, manual intervention may be required to complete the
230 merge.
231 +
232 As a noun: unless it is a <<def_fast_forward,fast-forward>>, a
233 successful merge results in the creation of a new <<def_commit,commit>>
234 representing the result of the merge, and having as
235 <<def_parent,parents>> the tips of the merged <<def_branch,branches>>.
236 This commit is referred to as a "merge commit", or sometimes just a
237 "merge".
238
239 [[def_object]]object::
240 The unit of storage in Git. It is uniquely identified by the
241 <<def_SHA1,SHA-1>> of its contents. Consequently, an
242 object can not be changed.
243
244 [[def_object_database]]object database::
245 Stores a set of "objects", and an individual <<def_object,object>> is
246 identified by its <<def_object_name,object name>>. The objects usually
247 live in `$GIT_DIR/objects/`.
248
249 [[def_object_identifier]]object identifier::
250 Synonym for <<def_object_name,object name>>.
251
252 [[def_object_name]]object name::
253 The unique identifier of an <<def_object,object>>. The
254 object name is usually represented by a 40 character
255 hexadecimal string. Also colloquially called <<def_SHA1,SHA-1>>.
256
257 [[def_object_type]]object type::
258 One of the identifiers "<<def_commit_object,commit>>",
259 "<<def_tree_object,tree>>", "<<def_tag_object,tag>>" or
260 "<<def_blob_object,blob>>" describing the type of an
261 <<def_object,object>>.
262
263 [[def_octopus]]octopus::
264 To <<def_merge,merge>> more than two <<def_branch,branches>>.
265
266 [[def_origin]]origin::
267 The default upstream <<def_repository,repository>>. Most projects have
268 at least one upstream project which they track. By default
269 'origin' is used for that purpose. New upstream updates
270 will be fetched into remote <<def_remote_tracking_branch,remote-tracking branches>> named
271 origin/name-of-upstream-branch, which you can see using
272 `git branch -r`.
273
274 [[def_pack]]pack::
275 A set of objects which have been compressed into one file (to save space
276 or to transmit them efficiently).
277
278 [[def_pack_index]]pack index::
279 The list of identifiers, and other information, of the objects in a
280 <<def_pack,pack>>, to assist in efficiently accessing the contents of a
281 pack.
282
283 [[def_pathspec]]pathspec::
284 Pattern used to limit paths in Git commands.
285 +
286 Pathspecs are used on the command line of "git ls-files", "git
287 ls-tree", "git add", "git grep", "git diff", "git checkout",
288 and many other commands to
289 limit the scope of operations to some subset of the tree or
290 worktree. See the documentation of each command for whether
291 paths are relative to the current directory or toplevel. The
292 pathspec syntax is as follows:
293 +
294 --
295
296 * any path matches itself
297 * the pathspec up to the last slash represents a
298 directory prefix. The scope of that pathspec is
299 limited to that subtree.
300 * the rest of the pathspec is a pattern for the remainder
301 of the pathname. Paths relative to the directory
302 prefix will be matched against that pattern using fnmatch(3);
303 in particular, '*' and '?' _can_ match directory separators.
304
305 --
306 +
307 For example, Documentation/*.jpg will match all .jpg files
308 in the Documentation subtree,
309 including Documentation/chapter_1/figure_1.jpg.
310 +
311 A pathspec that begins with a colon `:` has special meaning. In the
312 short form, the leading colon `:` is followed by zero or more "magic
313 signature" letters (which optionally is terminated by another colon `:`),
314 and the remainder is the pattern to match against the path. The optional
315 colon that terminates the "magic signature" can be omitted if the pattern
316 begins with a character that cannot be a "magic signature" and is not a
317 colon.
318 +
319 In the long form, the leading colon `:` is followed by a open
320 parenthesis `(`, a comma-separated list of zero or more "magic words",
321 and a close parentheses `)`, and the remainder is the pattern to match
322 against the path.
323 +
324 The "magic signature" consists of an ASCII symbol that is not
325 alphanumeric. Currently only the slash `/` is recognized as a
326 "magic signature": it makes the pattern match from the root of
327 the working tree, even when you are running the command from
328 inside a subdirectory.
329 +
330 A pathspec with only a colon means "there is no pathspec". This form
331 should not be combined with other pathspec.
332
333 [[def_parent]]parent::
334 A <<def_commit_object,commit object>> contains a (possibly empty) list
335 of the logical predecessor(s) in the line of development, i.e. its
336 parents.
337
338 [[def_pickaxe]]pickaxe::
339 The term <<def_pickaxe,pickaxe>> refers to an option to the diffcore
340 routines that help select changes that add or delete a given text
341 string. With the `--pickaxe-all` option, it can be used to view the full
342 <<def_changeset,changeset>> that introduced or removed, say, a
343 particular line of text. See linkgit:git-diff[1].
344
345 [[def_plumbing]]plumbing::
346 Cute name for <<def_core_git,core Git>>.
347
348 [[def_porcelain]]porcelain::
349 Cute name for programs and program suites depending on
350 <<def_core_git,core Git>>, presenting a high level access to
351 core Git. Porcelains expose more of a <<def_SCM,SCM>>
352 interface than the <<def_plumbing,plumbing>>.
353
354 [[def_pull]]pull::
355 Pulling a <<def_branch,branch>> means to <<def_fetch,fetch>> it and
356 <<def_merge,merge>> it. See also linkgit:git-pull[1].
357
358 [[def_push]]push::
359 Pushing a <<def_branch,branch>> means to get the branch's
360 <<def_head_ref,head ref>> from a remote <<def_repository,repository>>,
361 find out if it is a direct ancestor to the branch's local
362 head ref, and in that case, putting all
363 objects, which are <<def_reachable,reachable>> from the local
364 head ref, and which are missing from the remote
365 repository, into the remote
366 <<def_object_database,object database>>, and updating the remote
367 head ref. If the remote <<def_head,head>> is not an
368 ancestor to the local head, the push fails.
369
370 [[def_reachable]]reachable::
371 All of the ancestors of a given <<def_commit,commit>> are said to be
372 "reachable" from that commit. More
373 generally, one <<def_object,object>> is reachable from
374 another if we can reach the one from the other by a <<def_chain,chain>>
375 that follows <<def_tag,tags>> to whatever they tag,
376 <<def_commit_object,commits>> to their parents or trees, and
377 <<def_tree_object,trees>> to the trees or <<def_blob_object,blobs>>
378 that they contain.
379
380 [[def_rebase]]rebase::
381 To reapply a series of changes from a <<def_branch,branch>> to a
382 different base, and reset the <<def_head,head>> of that branch
383 to the result.
384
385 [[def_ref]]ref::
386 A 40-byte hex representation of a <<def_SHA1,SHA-1>> or a name that
387 denotes a particular <<def_object,object>>. They may be stored in
388 a file under `$GIT_DIR/refs/` directory, or
389 in the `$GIT_DIR/packed-refs` file.
390
391 [[def_reflog]]reflog::
392 A reflog shows the local "history" of a ref. In other words,
393 it can tell you what the 3rd last revision in _this_ repository
394 was, and what was the current state in _this_ repository,
395 yesterday 9:14pm. See linkgit:git-reflog[1] for details.
396
397 [[def_refspec]]refspec::
398 A "refspec" is used by <<def_fetch,fetch>> and
399 <<def_push,push>> to describe the mapping between remote
400 <<def_ref,ref>> and local ref.
401
402 [[def_remote_tracking_branch]]remote-tracking branch::
403 A <<def_ref,ref>> that is used to follow changes from another
404 <<def_repository,repository>>. It typically looks like
405 'refs/remotes/foo/bar' (indicating that it tracks a branch named
406 'bar' in a remote named 'foo'), and matches the right-hand-side of
407 a configured fetch <<def_refspec,refspec>>. A remote-tracking
408 branch should not contain direct modifications or have local
409 commits made to it.
410
411 [[def_repository]]repository::
412 A collection of <<def_ref,refs>> together with an
413 <<def_object_database,object database>> containing all objects
414 which are <<def_reachable,reachable>> from the refs, possibly
415 accompanied by meta data from one or more <<def_porcelain,porcelains>>. A
416 repository can share an object database with other repositories
417 via <<def_alternate_object_database,alternates mechanism>>.
418
419 [[def_resolve]]resolve::
420 The action of fixing up manually what a failed automatic
421 <<def_merge,merge>> left behind.
422
423 [[def_revision]]revision::
424 Synonym for <<def_commit,commit>> (the noun).
425
426 [[def_rewind]]rewind::
427 To throw away part of the development, i.e. to assign the
428 <<def_head,head>> to an earlier <<def_revision,revision>>.
429
430 [[def_SCM]]SCM::
431 Source code management (tool).
432
433 [[def_SHA1]]SHA-1::
434 "Secure Hash Algorithm 1"; a cryptographic hash function.
435 In the context of Git used as a synonym for <<def_object_name,object name>>.
436
437 [[def_shallow_repository]]shallow repository::
438 A shallow <<def_repository,repository>> has an incomplete
439 history some of whose <<def_commit,commits>> have <<def_parent,parents>> cauterized away (in other
440 words, Git is told to pretend that these commits do not have the
441 parents, even though they are recorded in the <<def_commit_object,commit
442 object>>). This is sometimes useful when you are interested only in the
443 recent history of a project even though the real history recorded in the
444 upstream is much larger. A shallow repository
445 is created by giving the `--depth` option to linkgit:git-clone[1], and
446 its history can be later deepened with linkgit:git-fetch[1].
447
448 [[def_symref]]symref::
449 Symbolic reference: instead of containing the <<def_SHA1,SHA-1>>
450 id itself, it is of the format 'ref: refs/some/thing' and when
451 referenced, it recursively dereferences to this reference.
452 '<<def_HEAD,HEAD>>' is a prime example of a symref. Symbolic
453 references are manipulated with the linkgit:git-symbolic-ref[1]
454 command.
455
456 [[def_tag]]tag::
457 A <<def_ref,ref>> under `refs/tags/` namespace that points to an
458 object of an arbitrary type (typically a tag points to either a
459 <<def_tag_object,tag>> or a <<def_commit_object,commit object>>).
460 In contrast to a <<def_head,head>>, a tag is not updated by
461 the `commit` command. A Git tag has nothing to do with a Lisp
462 tag (which would be called an <<def_object_type,object type>>
463 in Git's context). A tag is most typically used to mark a particular
464 point in the commit ancestry <<def_chain,chain>>.
465
466 [[def_tag_object]]tag object::
467 An <<def_object,object>> containing a <<def_ref,ref>> pointing to
468 another object, which can contain a message just like a
469 <<def_commit_object,commit object>>. It can also contain a (PGP)
470 signature, in which case it is called a "signed tag object".
471
472 [[def_topic_branch]]topic branch::
473 A regular Git <<def_branch,branch>> that is used by a developer to
474 identify a conceptual line of development. Since branches are very easy
475 and inexpensive, it is often desirable to have several small branches
476 that each contain very well defined concepts or small incremental yet
477 related changes.
478
479 [[def_tree]]tree::
480 Either a <<def_working_tree,working tree>>, or a <<def_tree_object,tree
481 object>> together with the dependent <<def_blob_object,blob>> and tree objects
482 (i.e. a stored representation of a working tree).
483
484 [[def_tree_object]]tree object::
485 An <<def_object,object>> containing a list of file names and modes along
486 with refs to the associated blob and/or tree objects. A
487 <<def_tree,tree>> is equivalent to a <<def_directory,directory>>.
488
489 [[def_tree-ish]]tree-ish::
490 A <<def_ref,ref>> pointing to either a <<def_commit_object,commit
491 object>>, a <<def_tree_object,tree object>>, or a <<def_tag_object,tag
492 object>> pointing to a tag or commit or tree object.
493
494 [[def_unmerged_index]]unmerged index::
495 An <<def_index,index>> which contains unmerged
496 <<def_index_entry,index entries>>.
497
498 [[def_unreachable_object]]unreachable object::
499 An <<def_object,object>> which is not <<def_reachable,reachable>> from a
500 <<def_branch,branch>>, <<def_tag,tag>>, or any other reference.
501
502 [[def_upstream_branch]]upstream branch::
503 The default <<def_branch,branch>> that is merged into the branch in
504 question (or the branch in question is rebased onto). It is configured
505 via branch.<name>.remote and branch.<name>.merge. If the upstream branch
506 of 'A' is 'origin/B' sometimes we say "'A' is tracking 'origin/B'".
507
508 [[def_working_tree]]working tree::
509 The tree of actual checked out files. The working tree normally
510 contains the contents of the <<def_HEAD,HEAD>> commit's tree,
511 plus any local changes that you have made but not yet committed.