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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 an "alternate".
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.
17 [[def_blob_object]]blob object::
18 Untyped <<def_object,object>>, e.g. the contents of a file.
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.
31 [[def_cache]]cache::
32 Obsolete for: <<def_index,index>>.
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>>).
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.
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>>.
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_commit-ish]]commit-ish (also committish)::
86 A <<def_commit_object,commit object>> or an
87 <<def_object,object>> that can be recursively dereferenced to
88 a commit object.
89 The following are all commit-ishes:
90 a commit object,
91 a <<def_tag_object,tag object>> that points to a commit
92 object,
93 a tag object that points to a tag object that points to a
94 commit object,
95 etc.
97 [[def_core_git]]core Git::
98 Fundamental data structures and utilities of Git. Exposes only limited
99 source code management tools.
101 [[def_DAG]]DAG::
102 Directed acyclic graph. The <<def_commit_object,commit objects>> form a
103 directed acyclic graph, because they have parents (directed), and the
104 graph of commit objects is acyclic (there is no <<def_chain,chain>>
105 which begins and ends with the same <<def_object,object>>).
107 [[def_dangling_object]]dangling object::
108 An <<def_unreachable_object,unreachable object>> which is not
109 <<def_reachable,reachable>> even from other unreachable objects; a
110 dangling object has no references to it from any
111 reference or <<def_object,object>> in the <<def_repository,repository>>.
113 [[def_detached_HEAD]]detached HEAD::
114 Normally the <<def_HEAD,HEAD>> stores the name of a
115 <<def_branch,branch>>, and commands that operate on the
116 history HEAD represents operate on the history leading to the
117 tip of the branch the HEAD points at. However, Git also
118 allows you to <<def_checkout,check out>> an arbitrary
119 <<def_commit,commit>> that isn't necessarily the tip of any
120 particular branch. The HEAD in such a state is called
121 "detached".
122 +
123 Note that commands that operate on the history of the current branch
124 (e.g. `git commit` to build a new history on top of it) still work
125 while the HEAD is detached. They update the HEAD to point at the tip
126 of the updated history without affecting any branch. Commands that
127 update or inquire information _about_ the current branch (e.g. `git
128 branch --set-upstream-to` that sets what remote-tracking branch the
129 current branch integrates with) obviously do not work, as there is no
130 (real) current branch to ask about in this state.
132 [[def_directory]]directory::
133 The list you get with "ls" :-)
135 [[def_dirty]]dirty::
136 A <<def_working_tree,working tree>> is said to be "dirty" if
137 it contains modifications which have not been <<def_commit,committed>> to the current
138 <<def_branch,branch>>.
140 [[def_evil_merge]]evil merge::
141 An evil merge is a <<def_merge,merge>> that introduces changes that
142 do not appear in any <<def_parent,parent>>.
144 [[def_fast_forward]]fast-forward::
145 A fast-forward is a special type of <<def_merge,merge>> where you have a
146 <<def_revision,revision>> and you are "merging" another
147 <<def_branch,branch>>'s changes that happen to be a descendant of what
148 you have. In such a case, you do not make a new <<def_merge,merge>>
149 <<def_commit,commit>> but instead just update to his
150 revision. This will happen frequently on a
151 <<def_remote_tracking_branch,remote-tracking branch>> of a remote
152 <<def_repository,repository>>.
154 [[def_fetch]]fetch::
155 Fetching a <<def_branch,branch>> means to get the
156 branch's <<def_head_ref,head ref>> from a remote
157 <<def_repository,repository>>, to find out which objects are
158 missing from the local <<def_object_database,object database>>,
159 and to get them, too. See also linkgit:git-fetch[1].
161 [[def_file_system]]file system::
162 Linus Torvalds originally designed Git to be a user space file system,
163 i.e. the infrastructure to hold files and directories. That ensured the
164 efficiency and speed of Git.
166 [[def_git_archive]]Git archive::
167 Synonym for <<def_repository,repository>> (for arch people).
169 [[def_gitfile]]gitfile::
170 A plain file `.git` at the root of a working tree that
171 points at the directory that is the real repository.
173 [[def_grafts]]grafts::
174 Grafts enables two otherwise different lines of development to be joined
175 together by recording fake ancestry information for commits. This way
176 you can make Git pretend the set of <<def_parent,parents>> a <<def_commit,commit>> has
177 is different from what was recorded when the commit was
178 created. Configured via the `.git/info/grafts` file.
179 +
180 Note that the grafts mechanism is outdated and can lead to problems
181 transferring objects between repositories; see linkgit:git-replace[1]
182 for a more flexible and robust system to do the same thing.
184 [[def_hash]]hash::
185 In Git's context, synonym for <<def_object_name,object name>>.
187 [[def_head]]head::
188 A <<def_ref,named reference>> to the <<def_commit,commit>> at the tip of a
189 <<def_branch,branch>>. Heads are stored in a file in
190 `$GIT_DIR/refs/heads/` directory, except when using packed refs. (See
191 linkgit:git-pack-refs[1].)
193 [[def_HEAD]]HEAD::
194 The current <<def_branch,branch>>. In more detail: Your <<def_working_tree,
195 working tree>> is normally derived from the state of the tree
196 referred to by HEAD. HEAD is a reference to one of the
197 <<def_head,heads>> in your repository, except when using a
198 <<def_detached_HEAD,detached HEAD>>, in which case it directly
199 references an arbitrary commit.
201 [[def_head_ref]]head ref::
202 A synonym for <<def_head,head>>.
204 [[def_hook]]hook::
205 During the normal execution of several Git commands, call-outs are made
206 to optional scripts that allow a developer to add functionality or
207 checking. Typically, the hooks allow for a command to be pre-verified
208 and potentially aborted, and allow for a post-notification after the
209 operation is done. The hook scripts are found in the
210 `$GIT_DIR/hooks/` directory, and are enabled by simply
211 removing the `.sample` suffix from the filename. In earlier versions
212 of Git you had to make them executable.
214 [[def_index]]index::
215 A collection of files with stat information, whose contents are stored
216 as objects. The index is a stored version of your
217 <<def_working_tree,working tree>>. Truth be told, it can also contain a second, and even
218 a third version of a working tree, which are used
219 when <<def_merge,merging>>.
221 [[def_index_entry]]index entry::
222 The information regarding a particular file, stored in the
223 <<def_index,index>>. An index entry can be unmerged, if a
224 <<def_merge,merge>> was started, but not yet finished (i.e. if
225 the index contains multiple versions of that file).
227 [[def_master]]master::
228 The default development <<def_branch,branch>>. Whenever you
229 create a Git <<def_repository,repository>>, a branch named
230 "master" is created, and becomes the active branch. In most
231 cases, this contains the local development, though that is
232 purely by convention and is not required.
234 [[def_merge]]merge::
235 As a verb: To bring the contents of another
236 <<def_branch,branch>> (possibly from an external
237 <<def_repository,repository>>) into the current branch. In the
238 case where the merged-in branch is from a different repository,
239 this is done by first <<def_fetch,fetching>> the remote branch
240 and then merging the result into the current branch. This
241 combination of fetch and merge operations is called a
242 <<def_pull,pull>>. Merging is performed by an automatic process
243 that identifies changes made since the branches diverged, and
244 then applies all those changes together. In cases where changes
245 conflict, manual intervention may be required to complete the
246 merge.
247 +
248 As a noun: unless it is a <<def_fast_forward,fast-forward>>, a
249 successful merge results in the creation of a new <<def_commit,commit>>
250 representing the result of the merge, and having as
251 <<def_parent,parents>> the tips of the merged <<def_branch,branches>>.
252 This commit is referred to as a "merge commit", or sometimes just a
253 "merge".
255 [[def_object]]object::
256 The unit of storage in Git. It is uniquely identified by the
257 <<def_SHA1,SHA-1>> of its contents. Consequently, an
258 object can not be changed.
260 [[def_object_database]]object database::
261 Stores a set of "objects", and an individual <<def_object,object>> is
262 identified by its <<def_object_name,object name>>. The objects usually
263 live in `$GIT_DIR/objects/`.
265 [[def_object_identifier]]object identifier::
266 Synonym for <<def_object_name,object name>>.
268 [[def_object_name]]object name::
269 The unique identifier of an <<def_object,object>>. The
270 object name is usually represented by a 40 character
271 hexadecimal string. Also colloquially called <<def_SHA1,SHA-1>>.
273 [[def_object_type]]object type::
274 One of the identifiers "<<def_commit_object,commit>>",
275 "<<def_tree_object,tree>>", "<<def_tag_object,tag>>" or
276 "<<def_blob_object,blob>>" describing the type of an
277 <<def_object,object>>.
279 [[def_octopus]]octopus::
280 To <<def_merge,merge>> more than two <<def_branch,branches>>.
282 [[def_origin]]origin::
283 The default upstream <<def_repository,repository>>. Most projects have
284 at least one upstream project which they track. By default
285 'origin' is used for that purpose. New upstream updates
286 will be fetched into <<def_remote_tracking_branch,remote-tracking branches>> named
287 origin/name-of-upstream-branch, which you can see using
288 `git branch -r`.
290 [[def_pack]]pack::
291 A set of objects which have been compressed into one file (to save space
292 or to transmit them efficiently).
294 [[def_pack_index]]pack index::
295 The list of identifiers, and other information, of the objects in a
296 <<def_pack,pack>>, to assist in efficiently accessing the contents of a
297 pack.
299 [[def_pathspec]]pathspec::
300 Pattern used to limit paths in Git commands.
301 +
302 Pathspecs are used on the command line of "git ls-files", "git
303 ls-tree", "git add", "git grep", "git diff", "git checkout",
304 and many other commands to
305 limit the scope of operations to some subset of the tree or
306 worktree. See the documentation of each command for whether
307 paths are relative to the current directory or toplevel. The
308 pathspec syntax is as follows:
309 +
310 --
312 * any path matches itself
313 * the pathspec up to the last slash represents a
314 directory prefix. The scope of that pathspec is
315 limited to that subtree.
316 * the rest of the pathspec is a pattern for the remainder
317 of the pathname. Paths relative to the directory
318 prefix will be matched against that pattern using fnmatch(3);
319 in particular, '*' and '?' _can_ match directory separators.
321 --
322 +
323 For example, Documentation/*.jpg will match all .jpg files
324 in the Documentation subtree,
325 including Documentation/chapter_1/figure_1.jpg.
326 +
327 A pathspec that begins with a colon `:` has special meaning. In the
328 short form, the leading colon `:` is followed by zero or more "magic
329 signature" letters (which optionally is terminated by another colon `:`),
330 and the remainder is the pattern to match against the path.
331 The "magic signature" consists of ASCII symbols that are neither
332 alphanumeric, glob, regex special characters nor colon.
333 The optional colon that terminates the "magic signature" can be
334 omitted if the pattern begins with a character that does not belong to
335 "magic signature" symbol set and is not a colon.
336 +
337 In the long form, the leading colon `:` is followed by a open
338 parenthesis `(`, a comma-separated list of zero or more "magic words",
339 and a close parentheses `)`, and the remainder is the pattern to match
340 against the path.
341 +
342 A pathspec with only a colon means "there is no pathspec". This form
343 should not be combined with other pathspec.
344 +
345 --
346 top;;
347 The magic word `top` (magic signature: `/`) makes the pattern
348 match from the root of the working tree, even when you are
349 running the command from inside a subdirectory.
351 literal;;
352 Wildcards in the pattern such as `*` or `?` are treated
353 as literal characters.
355 icase;;
356 Case insensitive match.
358 glob;;
359 Git treats the pattern as a shell glob suitable for
360 consumption by fnmatch(3) with the FNM_PATHNAME flag:
361 wildcards in the pattern will not match a / in the pathname.
362 For example, "Documentation/{asterisk}.html" matches
363 "Documentation/git.html" but not "Documentation/ppc/ppc.html"
364 or "tools/perf/Documentation/perf.html".
365 +
366 Two consecutive asterisks ("`**`") in patterns matched against
367 full pathname may have special meaning:
369 - A leading "`**`" followed by a slash means match in all
370 directories. For example, "`**/foo`" matches file or directory
371 "`foo`" anywhere, the same as pattern "`foo`". "`**/foo/bar`"
372 matches file or directory "`bar`" anywhere that is directly
373 under directory "`foo`".
375 - A trailing "`/**`" matches everything inside. For example,
376 "`abc/**`" matches all files inside directory "abc", relative
377 to the location of the `.gitignore` file, with infinite depth.
379 - A slash followed by two consecutive asterisks then a slash
380 matches zero or more directories. For example, "`a/**/b`"
381 matches "`a/b`", "`a/x/b`", "`a/x/y/b`" and so on.
383 - Other consecutive asterisks are considered invalid.
384 +
385 Glob magic is incompatible with literal magic.
387 attr;;
388 After `attr:` comes a space separated list of "attribute
389 requirements", all of which must be met in order for the
390 path to be considered a match; this is in addition to the
391 usual non-magic pathspec pattern matching.
392 See linkgit:gitattributes[5].
393 +
394 Each of the attribute requirements for the path takes one of
395 these forms:
397 - "`ATTR`" requires that the attribute `ATTR` be set.
399 - "`-ATTR`" requires that the attribute `ATTR` be unset.
401 - "`ATTR=VALUE`" requires that the attribute `ATTR` be
402 set to the string `VALUE`.
404 - "`!ATTR`" requires that the attribute `ATTR` be
405 unspecified.
406 +
408 exclude;;
409 After a path matches any non-exclude pathspec, it will be run
410 through all exclude pathspecs (magic signature: `!` or its
411 synonym `^`). If it matches, the path is ignored. When there
412 is no non-exclude pathspec, the exclusion is applied to the
413 result set as if invoked without any pathspec.
414 --
416 [[def_parent]]parent::
417 A <<def_commit_object,commit object>> contains a (possibly empty) list
418 of the logical predecessor(s) in the line of development, i.e. its
419 parents.
421 [[def_pickaxe]]pickaxe::
422 The term <<def_pickaxe,pickaxe>> refers to an option to the diffcore
423 routines that help select changes that add or delete a given text
424 string. With the `--pickaxe-all` option, it can be used to view the full
425 <<def_changeset,changeset>> that introduced or removed, say, a
426 particular line of text. See linkgit:git-diff[1].
428 [[def_plumbing]]plumbing::
429 Cute name for <<def_core_git,core Git>>.
431 [[def_porcelain]]porcelain::
432 Cute name for programs and program suites depending on
433 <<def_core_git,core Git>>, presenting a high level access to
434 core Git. Porcelains expose more of a <<def_SCM,SCM>>
435 interface than the <<def_plumbing,plumbing>>.
437 [[def_per_worktree_ref]]per-worktree ref::
438 Refs that are per-<<def_working_tree,worktree>>, rather than
439 global. This is presently only <<def_HEAD,HEAD>> and any refs
440 that start with `refs/bisect/`, but might later include other
441 unusual refs.
443 [[def_pseudoref]]pseudoref::
444 Pseudorefs are a class of files under `$GIT_DIR` which behave
445 like refs for the purposes of rev-parse, but which are treated
446 specially by git. Pseudorefs both have names that are all-caps,
447 and always start with a line consisting of a
448 <<def_SHA1,SHA-1>> followed by whitespace. So, HEAD is not a
449 pseudoref, because it is sometimes a symbolic ref. They might
450 optionally contain some additional data. `MERGE_HEAD` and
451 `CHERRY_PICK_HEAD` are examples. Unlike
452 <<def_per_worktree_ref,per-worktree refs>>, these files cannot
453 be symbolic refs, and never have reflogs. They also cannot be
454 updated through the normal ref update machinery. Instead,
455 they are updated by directly writing to the files. However,
456 they can be read as if they were refs, so `git rev-parse
457 MERGE_HEAD` will work.
459 [[def_pull]]pull::
460 Pulling a <<def_branch,branch>> means to <<def_fetch,fetch>> it and
461 <<def_merge,merge>> it. See also linkgit:git-pull[1].
463 [[def_push]]push::
464 Pushing a <<def_branch,branch>> means to get the branch's
465 <<def_head_ref,head ref>> from a remote <<def_repository,repository>>,
466 find out if it is a direct ancestor to the branch's local
467 head ref, and in that case, putting all
468 objects, which are <<def_reachable,reachable>> from the local
469 head ref, and which are missing from the remote
470 repository, into the remote
471 <<def_object_database,object database>>, and updating the remote
472 head ref. If the remote <<def_head,head>> is not an
473 ancestor to the local head, the push fails.
475 [[def_reachable]]reachable::
476 All of the ancestors of a given <<def_commit,commit>> are said to be
477 "reachable" from that commit. More
478 generally, one <<def_object,object>> is reachable from
479 another if we can reach the one from the other by a <<def_chain,chain>>
480 that follows <<def_tag,tags>> to whatever they tag,
481 <<def_commit_object,commits>> to their parents or trees, and
482 <<def_tree_object,trees>> to the trees or <<def_blob_object,blobs>>
483 that they contain.
485 [[def_rebase]]rebase::
486 To reapply a series of changes from a <<def_branch,branch>> to a
487 different base, and reset the <<def_head,head>> of that branch
488 to the result.
490 [[def_ref]]ref::
491 A name that begins with `refs/` (e.g. `refs/heads/master`)
492 that points to an <<def_object_name,object name>> or another
493 ref (the latter is called a <<def_symref,symbolic ref>>).
494 For convenience, a ref can sometimes be abbreviated when used
495 as an argument to a Git command; see linkgit:gitrevisions[7]
496 for details.
497 Refs are stored in the <<def_repository,repository>>.
498 +
499 The ref namespace is hierarchical.
500 Different subhierarchies are used for different purposes (e.g. the
501 `refs/heads/` hierarchy is used to represent local branches).
502 +
503 There are a few special-purpose refs that do not begin with `refs/`.
504 The most notable example is `HEAD`.
506 [[def_reflog]]reflog::
507 A reflog shows the local "history" of a ref. In other words,
508 it can tell you what the 3rd last revision in _this_ repository
509 was, and what was the current state in _this_ repository,
510 yesterday 9:14pm. See linkgit:git-reflog[1] for details.
512 [[def_refspec]]refspec::
513 A "refspec" is used by <<def_fetch,fetch>> and
514 <<def_push,push>> to describe the mapping between remote
515 <<def_ref,ref>> and local ref.
517 [[def_remote]]remote repository::
518 A <<def_repository,repository>> which is used to track the same
519 project but resides somewhere else. To communicate with remotes,
520 see <<def_fetch,fetch>> or <<def_push,push>>.
522 [[def_remote_tracking_branch]]remote-tracking branch::
523 A <<def_ref,ref>> that is used to follow changes from another
524 <<def_repository,repository>>. It typically looks like
525 'refs/remotes/foo/bar' (indicating that it tracks a branch named
526 'bar' in a remote named 'foo'), and matches the right-hand-side of
527 a configured fetch <<def_refspec,refspec>>. A remote-tracking
528 branch should not contain direct modifications or have local
529 commits made to it.
531 [[def_repository]]repository::
532 A collection of <<def_ref,refs>> together with an
533 <<def_object_database,object database>> containing all objects
534 which are <<def_reachable,reachable>> from the refs, possibly
535 accompanied by meta data from one or more <<def_porcelain,porcelains>>. A
536 repository can share an object database with other repositories
537 via <<def_alternate_object_database,alternates mechanism>>.
539 [[def_resolve]]resolve::
540 The action of fixing up manually what a failed automatic
541 <<def_merge,merge>> left behind.
543 [[def_revision]]revision::
544 Synonym for <<def_commit,commit>> (the noun).
546 [[def_rewind]]rewind::
547 To throw away part of the development, i.e. to assign the
548 <<def_head,head>> to an earlier <<def_revision,revision>>.
550 [[def_SCM]]SCM::
551 Source code management (tool).
553 [[def_SHA1]]SHA-1::
554 "Secure Hash Algorithm 1"; a cryptographic hash function.
555 In the context of Git used as a synonym for <<def_object_name,object name>>.
557 [[def_shallow_clone]]shallow clone::
558 Mostly a synonym to <<def_shallow_repository,shallow repository>>
559 but the phrase makes it more explicit that it was created by
560 running `git clone --depth=...` command.
562 [[def_shallow_repository]]shallow repository::
563 A shallow <<def_repository,repository>> has an incomplete
564 history some of whose <<def_commit,commits>> have <<def_parent,parents>> cauterized away (in other
565 words, Git is told to pretend that these commits do not have the
566 parents, even though they are recorded in the <<def_commit_object,commit
567 object>>). This is sometimes useful when you are interested only in the
568 recent history of a project even though the real history recorded in the
569 upstream is much larger. A shallow repository
570 is created by giving the `--depth` option to linkgit:git-clone[1], and
571 its history can be later deepened with linkgit:git-fetch[1].
573 [[def_stash]]stash entry::
574 An <<def_object,object>> used to temporarily store the contents of a
575 <<def_dirty,dirty>> working directory and the index for future reuse.
577 [[def_submodule]]submodule::
578 A <<def_repository,repository>> that holds the history of a
579 separate project inside another repository (the latter of
580 which is called <<def_superproject, superproject>>).
582 [[def_superproject]]superproject::
583 A <<def_repository,repository>> that references repositories
584 of other projects in its working tree as <<def_submodule,submodules>>.
585 The superproject knows about the names of (but does not hold
586 copies of) commit objects of the contained submodules.
588 [[def_symref]]symref::
589 Symbolic reference: instead of containing the <<def_SHA1,SHA-1>>
590 id itself, it is of the format 'ref: refs/some/thing' and when
591 referenced, it recursively dereferences to this reference.
592 '<<def_HEAD,HEAD>>' is a prime example of a symref. Symbolic
593 references are manipulated with the linkgit:git-symbolic-ref[1]
594 command.
596 [[def_tag]]tag::
597 A <<def_ref,ref>> under `refs/tags/` namespace that points to an
598 object of an arbitrary type (typically a tag points to either a
599 <<def_tag_object,tag>> or a <<def_commit_object,commit object>>).
600 In contrast to a <<def_head,head>>, a tag is not updated by
601 the `commit` command. A Git tag has nothing to do with a Lisp
602 tag (which would be called an <<def_object_type,object type>>
603 in Git's context). A tag is most typically used to mark a particular
604 point in the commit ancestry <<def_chain,chain>>.
606 [[def_tag_object]]tag object::
607 An <<def_object,object>> containing a <<def_ref,ref>> pointing to
608 another object, which can contain a message just like a
609 <<def_commit_object,commit object>>. It can also contain a (PGP)
610 signature, in which case it is called a "signed tag object".
612 [[def_topic_branch]]topic branch::
613 A regular Git <<def_branch,branch>> that is used by a developer to
614 identify a conceptual line of development. Since branches are very easy
615 and inexpensive, it is often desirable to have several small branches
616 that each contain very well defined concepts or small incremental yet
617 related changes.
619 [[def_tree]]tree::
620 Either a <<def_working_tree,working tree>>, or a <<def_tree_object,tree
621 object>> together with the dependent <<def_blob_object,blob>> and tree objects
622 (i.e. a stored representation of a working tree).
624 [[def_tree_object]]tree object::
625 An <<def_object,object>> containing a list of file names and modes along
626 with refs to the associated blob and/or tree objects. A
627 <<def_tree,tree>> is equivalent to a <<def_directory,directory>>.
629 [[def_tree-ish]]tree-ish (also treeish)::
630 A <<def_tree_object,tree object>> or an <<def_object,object>>
631 that can be recursively dereferenced to a tree object.
632 Dereferencing a <<def_commit_object,commit object>> yields the
633 tree object corresponding to the <<def_revision,revision>>'s
634 top <<def_directory,directory>>.
635 The following are all tree-ishes:
636 a <<def_commit-ish,commit-ish>>,
637 a tree object,
638 a <<def_tag_object,tag object>> that points to a tree object,
639 a tag object that points to a tag object that points to a tree
640 object,
641 etc.
643 [[def_unmerged_index]]unmerged index::
644 An <<def_index,index>> which contains unmerged
645 <<def_index_entry,index entries>>.
647 [[def_unreachable_object]]unreachable object::
648 An <<def_object,object>> which is not <<def_reachable,reachable>> from a
649 <<def_branch,branch>>, <<def_tag,tag>>, or any other reference.
651 [[def_upstream_branch]]upstream branch::
652 The default <<def_branch,branch>> that is merged into the branch in
653 question (or the branch in question is rebased onto). It is configured
654 via branch.<name>.remote and branch.<name>.merge. If the upstream branch
655 of 'A' is 'origin/B' sometimes we say "'A' is tracking 'origin/B'".
657 [[def_working_tree]]working tree::
658 The tree of actual checked out files. The working tree normally
659 contains the contents of the <<def_HEAD,HEAD>> commit's tree,
660 plus any local changes that you have made but not yet committed.