Merge branch 'jc/grep'
[git/git.git] / Documentation / glossary.txt
1 alternate object database::
2 Via the alternates mechanism, a repository can inherit part of its
3 object database from another object database, which is called
4 "alternate".
5
6 bare repository::
7 A bare repository is normally an appropriately named
8 directory with a `.git` suffix that does not have a
9 locally checked-out copy of any of the files under revision
10 control. That is, all of the `git` administrative and
11 control files that would normally be present in the
12 hidden `.git` sub-directory are directly present in
13 the `repository.git` directory instead, and no other files
14 are present and checked out. Usually publishers of public
15 repositories make bare repositories available.
16
17 blob object::
18 Untyped object, e.g. the contents of a file.
19
20 branch::
21 A non-cyclical graph of revisions, i.e. the complete history of
22 a particular revision, which is called the branch head. The
23 branch heads are stored in `$GIT_DIR/refs/heads/`.
24
25 cache::
26 Obsolete for: index.
27
28 chain::
29 A list of objects, where each object in the list contains a
30 reference to its successor (for example, the successor of a commit
31 could be one of its parents).
32
33 changeset::
34 BitKeeper/cvsps speak for "commit". Since git does not store
35 changes, but states, it really does not make sense to use
36 the term "changesets" with git.
37
38 checkout::
39 The action of updating the working tree to a revision which was
40 stored in the object database.
41
42 cherry-picking::
43 In SCM jargon, "cherry pick" means to choose a subset of
44 changes out of a series of changes (typically commits)
45 and record them as a new series of changes on top of
46 different codebase. In GIT, this is performed by
47 "git cherry-pick" command to extract the change
48 introduced by an existing commit and to record it based
49 on the tip of the current branch as a new commit.
50
51 clean::
52 A working tree is clean, if it corresponds to the revision
53 referenced by the current head. Also see "dirty".
54
55 commit::
56 As a verb: The action of storing the current state of the index in the
57 object database. The result is a revision.
58 As a noun: Short hand for commit object.
59
60 commit object::
61 An object which contains the information about a particular
62 revision, such as parents, committer, author, date and the
63 tree object which corresponds to the top directory of the
64 stored revision.
65
66 core git::
67 Fundamental data structures and utilities of git. Exposes only
68 limited source code management tools.
69
70 DAG::
71 Directed acyclic graph. The commit objects form a directed acyclic
72 graph, because they have parents (directed), and the graph of commit
73 objects is acyclic (there is no chain which begins and ends with the
74 same object).
75
76 dircache::
77 You are *waaaaay* behind.
78
79 dirty::
80 A working tree is said to be dirty if it contains modifications
81 which have not been committed to the current branch.
82
83 directory::
84 The list you get with "ls" :-)
85
86 ent::
87 Favorite synonym to "tree-ish" by some total geeks. See
88 `http://en.wikipedia.org/wiki/Ent_(Middle-earth)` for an in-depth
89 explanation.
90
91 fast forward::
92 A fast-forward is a special type of merge where you have
93 a revision and you are "merging" another branch's changes
94 that happen to be a descendant of what you have.
95 In such these cases, you do not make a new merge commit but
96 instead just update to his revision. This will happen
97 frequently on a tracking branch of a remote repository.
98
99 fetch::
100 Fetching a branch means to get the branch's head ref from a
101 remote repository, to find out which objects are missing from
102 the local object database, and to get them, too.
103
104 file system::
105 Linus Torvalds originally designed git to be a user space file
106 system, i.e. the infrastructure to hold files and directories.
107 That ensured the efficiency and speed of git.
108
109 git archive::
110 Synonym for repository (for arch people).
111
112 hash::
113 In git's context, synonym to object name.
114
115 head::
116 The top of a branch. It contains a ref to the corresponding
117 commit object.
118
119 head ref::
120 A ref pointing to a head. Often, this is abbreviated to "head".
121 Head refs are stored in `$GIT_DIR/refs/heads/`.
122
123 hook::
124 During the normal execution of several git commands,
125 call-outs are made to optional scripts that allow
126 a developer to add functionality or checking.
127 Typically, the hooks allow for a command to be pre-verified
128 and potentially aborted, and allow for a post-notification
129 after the operation is done.
130 The hook scripts are found in the `$GIT_DIR/hooks/` directory,
131 and are enabled by simply making them executable.
132
133 index::
134 A collection of files with stat information, whose contents are
135 stored as objects. The index is a stored version of your working
136 tree. Truth be told, it can also contain a second, and even a third
137 version of a working tree, which are used when merging.
138
139 index entry::
140 The information regarding a particular file, stored in the index.
141 An index entry can be unmerged, if a merge was started, but not
142 yet finished (i.e. if the index contains multiple versions of
143 that file).
144
145 master::
146 The default development branch. Whenever you create a git
147 repository, a branch named "master" is created, and becomes
148 the active branch. In most cases, this contains the local
149 development, though that is purely conventional and not required.
150
151 merge::
152 To merge branches means to try to accumulate the changes since a
153 common ancestor and apply them to the first branch. An automatic
154 merge uses heuristics to accomplish that. Evidently, an automatic
155 merge can fail.
156
157 object::
158 The unit of storage in git. It is uniquely identified by
159 the SHA1 of its contents. Consequently, an object can not
160 be changed.
161
162 object database::
163 Stores a set of "objects", and an individual object is identified
164 by its object name. The objects usually live in `$GIT_DIR/objects/`.
165
166 object identifier::
167 Synonym for object name.
168
169 object name::
170 The unique identifier of an object. The hash of the object's contents
171 using the Secure Hash Algorithm 1 and usually represented by the 40
172 character hexadecimal encoding of the hash of the object (possibly
173 followed by a white space).
174
175 object type:
176 One of the identifiers "commit","tree","tag" and "blob" describing
177 the type of an object.
178
179 octopus::
180 To merge more than two branches. Also denotes an intelligent
181 predator.
182
183 origin::
184 The default upstream tracking branch. Most projects have at
185 least one upstream project which they track. By default
186 'origin' is used for that purpose. New upstream updates
187 will be fetched into this branch; you should never commit
188 to it yourself.
189
190 pack::
191 A set of objects which have been compressed into one file (to save
192 space or to transmit them efficiently).
193
194 pack index::
195 The list of identifiers, and other information, of the objects in a
196 pack, to assist in efficiently accessing the contents of a pack.
197
198 parent::
199 A commit object contains a (possibly empty) list of the logical
200 predecessor(s) in the line of development, i.e. its parents.
201
202 pickaxe::
203 The term pickaxe refers to an option to the diffcore routines
204 that help select changes that add or delete a given text string.
205 With the --pickaxe-all option, it can be used to view the
206 full changeset that introduced or removed, say, a particular
207 line of text. See gitlink:git-diff[1].
208
209 plumbing::
210 Cute name for core git.
211
212 porcelain::
213 Cute name for programs and program suites depending on core git,
214 presenting a high level access to core git. Porcelains expose
215 more of a SCM interface than the plumbing.
216
217 pull::
218 Pulling a branch means to fetch it and merge it.
219
220 push::
221 Pushing a branch means to get the branch's head ref from a remote
222 repository, find out if it is an ancestor to the branch's local
223 head ref is a direct, and in that case, putting all objects, which
224 are reachable from the local head ref, and which are missing from
225 the remote repository, into the remote object database, and updating
226 the remote head ref. If the remote head is not an ancestor to the
227 local head, the push fails.
228
229 reachable::
230 An object is reachable from a ref/commit/tree/tag, if there is a
231 chain leading from the latter to the former.
232
233 rebase::
234 To clean a branch by starting from the head of the main line of
235 development ("master"), and reapply the (possibly cherry-picked)
236 changes from that branch.
237
238 ref::
239 A 40-byte hex representation of a SHA1 or a name that denotes
240 a particular object. These may be stored in `$GIT_DIR/refs/`.
241
242 refspec::
243 A refspec is used by fetch and push to describe the mapping
244 between remote ref and local ref. They are combined with
245 a colon in the format <src>:<dst>, preceded by an optional
246 plus sign, +. For example:
247 `git fetch $URL refs/heads/master:refs/heads/origin`
248 means "grab the master branch head from the $URL and store
249 it as my origin branch head".
250 And `git push $URL refs/heads/master:refs/heads/to-upstream`
251 means "publish my master branch head as to-upstream master head
252 at $URL". See also gitlink:git-push[1]
253
254 repository::
255 A collection of refs together with an object database containing
256 all objects, which are reachable from the refs, possibly accompanied
257 by meta data from one or more porcelains. A repository can
258 share an object database with other repositories.
259
260 resolve::
261 The action of fixing up manually what a failed automatic merge
262 left behind.
263
264 revision::
265 A particular state of files and directories which was stored in
266 the object database. It is referenced by a commit object.
267
268 rewind::
269 To throw away part of the development, i.e. to assign the head to
270 an earlier revision.
271
272 SCM::
273 Source code management (tool).
274
275 SHA1::
276 Synonym for object name.
277
278 topic branch::
279 A regular git branch that is used by a developer to
280 identify a conceptual line of development. Since branches
281 are very easy and inexpensive, it is often desirable to
282 have several small branches that each contain very well
283 defined concepts or small incremental yet related changes.
284
285 tracking branch::
286 A regular git branch that is used to follow changes from
287 another repository. A tracking branch should not contain
288 direct modifications or have local commits made to it.
289 A tracking branch can usually be identified as the
290 right-hand-side ref in a Pull: refspec.
291
292 tree object::
293 An object containing a list of file names and modes along with refs
294 to the associated blob and/or tree objects. A tree is equivalent
295 to a directory.
296
297 tree::
298 Either a working tree, or a tree object together with the
299 dependent blob and tree objects (i.e. a stored representation
300 of a working tree).
301
302 tree-ish::
303 A ref pointing to either a commit object, a tree object, or a
304 tag object pointing to a tag or commit or tree object.
305
306 tag object::
307 An object containing a ref pointing to another object, which can
308 contain a message just like a commit object. It can also
309 contain a (PGP) signature, in which case it is called a "signed
310 tag object".
311
312 tag::
313 A ref pointing to a tag or commit object. In contrast to a head,
314 a tag is not changed by a commit. Tags (not tag objects) are
315 stored in `$GIT_DIR/refs/tags/`. A git tag has nothing to do with
316 a Lisp tag (which is called object type in git's context).
317 A tag is most typically used to mark a particular point in the
318 commit ancestry chain.
319
320 unmerged index:
321 An index which contains unmerged index entries.
322
323 working tree::
324 The set of files and directories currently being worked on,
325 i.e. you can work in your working tree without using git at all.
326