git-remote.txt: fix example url
[git/git.git] / Documentation / user-manual.txt
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0eb4f7cd 1Git User's Manual (for version 1.5.3 or newer)
71f4b183 2______________________________________________
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4
5Git is a fast distributed revision control system.
6
02783075 7This manual is designed to be readable by someone with basic UNIX
79c96c57 8command-line skills, but no previous knowledge of git.
d19fbc3c 9
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10<<repositories-and-branches>> and <<exploring-git-history>> explain how
11to fetch and study a project using git--read these chapters to learn how
12to build and test a particular version of a software project, search for
13regressions, and so on.
ef89f701 14
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15People needing to do actual development will also want to read
16<<Developing-with-git>> and <<sharing-development>>.
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17
18Further chapters cover more specialized topics.
19
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20Comprehensive reference documentation is available through the man
21pages. For a command such as "git clone", just use
22
23------------------------------------------------
24$ man git-clone
25------------------------------------------------
26
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27See also <<git-quick-start>> for a brief overview of git commands,
28without any explanation.
b181d57f 29
99f171bb 30Finally, see <<todo>> for ways that you can help make this manual more
2624d9a5 31complete.
b181d57f 32
b181d57f 33
e34caace 34[[repositories-and-branches]]
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35Repositories and Branches
36=========================
37
e34caace 38[[how-to-get-a-git-repository]]
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39How to get a git repository
40---------------------------
41
42It will be useful to have a git repository to experiment with as you
43read this manual.
44
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45The best way to get one is by using the gitlink:git-clone[1] command to
46download a copy of an existing repository. If you don't already have a
47project in mind, here are some interesting examples:
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48
49------------------------------------------------
50 # git itself (approx. 10MB download):
51$ git clone git://git.kernel.org/pub/scm/git/git.git
52 # the linux kernel (approx. 150MB download):
53$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
54------------------------------------------------
55
56The initial clone may be time-consuming for a large project, but you
57will only need to clone once.
58
59The clone command creates a new directory named after the project
60("git" or "linux-2.6" in the examples above). After you cd into this
61directory, you will see that it contains a copy of the project files,
62together with a special top-level directory named ".git", which
63contains all the information about the history of the project.
64
e34caace 65[[how-to-check-out]]
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66How to check out a different version of a project
67-------------------------------------------------
68
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69Git is best thought of as a tool for storing the history of a collection
70of files. It stores the history as a compressed collection of
71interrelated snapshots of the project's contents. In git each such
72version is called a <<def_commit,commit>>.
d19fbc3c 73
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74A single git repository may contain multiple branches. It keeps track
75of them by keeping a list of <<def_head,heads>> which reference the
a2ef9d63 76latest commit on each branch; the gitlink:git-branch[1] command shows
81b6c950 77you the list of branch heads:
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78
79------------------------------------------------
80$ git branch
81* master
82------------------------------------------------
83
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84A freshly cloned repository contains a single branch head, by default
85named "master", with the working directory initialized to the state of
86the project referred to by that branch head.
d19fbc3c 87
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88Most projects also use <<def_tag,tags>>. Tags, like heads, are
89references into the project's history, and can be listed using the
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90gitlink:git-tag[1] command:
91
92------------------------------------------------
93$ git tag -l
94v2.6.11
95v2.6.11-tree
96v2.6.12
97v2.6.12-rc2
98v2.6.12-rc3
99v2.6.12-rc4
100v2.6.12-rc5
101v2.6.12-rc6
102v2.6.13
103...
104------------------------------------------------
105
fe4b3e59 106Tags are expected to always point at the same version of a project,
81b6c950 107while heads are expected to advance as development progresses.
fe4b3e59 108
81b6c950 109Create a new branch head pointing to one of these versions and check it
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110out using gitlink:git-checkout[1]:
111
112------------------------------------------------
113$ git checkout -b new v2.6.13
114------------------------------------------------
115
116The working directory then reflects the contents that the project had
117when it was tagged v2.6.13, and gitlink:git-branch[1] shows two
118branches, with an asterisk marking the currently checked-out branch:
119
120------------------------------------------------
121$ git branch
122 master
123* new
124------------------------------------------------
125
126If you decide that you'd rather see version 2.6.17, you can modify
127the current branch to point at v2.6.17 instead, with
128
129------------------------------------------------
130$ git reset --hard v2.6.17
131------------------------------------------------
132
81b6c950 133Note that if the current branch head was your only reference to a
d19fbc3c 134particular point in history, then resetting that branch may leave you
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135with no way to find the history it used to point to; so use this command
136carefully.
d19fbc3c 137
e34caace 138[[understanding-commits]]
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139Understanding History: Commits
140------------------------------
141
142Every change in the history of a project is represented by a commit.
143The gitlink:git-show[1] command shows the most recent commit on the
144current branch:
145
146------------------------------------------------
147$ git show
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148commit 17cf781661e6d38f737f15f53ab552f1e95960d7
149Author: Linus Torvalds <torvalds@ppc970.osdl.org.(none)>
150Date: Tue Apr 19 14:11:06 2005 -0700
151
152 Remove duplicate getenv(DB_ENVIRONMENT) call
153
154 Noted by Tony Luck.
155
156diff --git a/init-db.c b/init-db.c
157index 65898fa..b002dc6 100644
158--- a/init-db.c
159+++ b/init-db.c
160@@ -7,7 +7,7 @@
d19fbc3c 161
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162 int main(int argc, char **argv)
163 {
164- char *sha1_dir = getenv(DB_ENVIRONMENT), *path;
165+ char *sha1_dir, *path;
166 int len, i;
167
168 if (mkdir(".git", 0755) < 0) {
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169------------------------------------------------
170
171As you can see, a commit shows who made the latest change, what they
172did, and why.
173
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174Every commit has a 40-hexdigit id, sometimes called the "object name" or the
175"SHA1 id", shown on the first line of the "git show" output. You can usually
176refer to a commit by a shorter name, such as a tag or a branch name, but this
177longer name can also be useful. Most importantly, it is a globally unique
178name for this commit: so if you tell somebody else the object name (for
179example in email), then you are guaranteed that name will refer to the same
180commit in their repository that it does in yours (assuming their repository
181has that commit at all). Since the object name is computed as a hash over the
182contents of the commit, you are guaranteed that the commit can never change
183without its name also changing.
184
036f8199 185In fact, in <<git-concepts>> we shall see that everything stored in git
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186history, including file data and directory contents, is stored in an object
187with a name that is a hash of its contents.
d19fbc3c 188
e34caace 189[[understanding-reachability]]
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190Understanding history: commits, parents, and reachability
191~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
192
193Every commit (except the very first commit in a project) also has a
194parent commit which shows what happened before this commit.
195Following the chain of parents will eventually take you back to the
196beginning of the project.
197
198However, the commits do not form a simple list; git allows lines of
199development to diverge and then reconverge, and the point where two
200lines of development reconverge is called a "merge". The commit
201representing a merge can therefore have more than one parent, with
202each parent representing the most recent commit on one of the lines
203of development leading to that point.
204
205The best way to see how this works is using the gitlink:gitk[1]
206command; running gitk now on a git repository and looking for merge
207commits will help understand how the git organizes history.
208
209In the following, we say that commit X is "reachable" from commit Y
210if commit X is an ancestor of commit Y. Equivalently, you could say
02783075 211that Y is a descendant of X, or that there is a chain of parents
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212leading from commit Y to commit X.
213
e34caace 214[[history-diagrams]]
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215Understanding history: History diagrams
216~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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217
218We will sometimes represent git history using diagrams like the one
219below. Commits are shown as "o", and the links between them with
220lines drawn with - / and \. Time goes left to right:
221
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222
223................................................
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224 o--o--o <-- Branch A
225 /
226 o--o--o <-- master
227 \
228 o--o--o <-- Branch B
1dc71a91 229................................................
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230
231If we need to talk about a particular commit, the character "o" may
232be replaced with another letter or number.
233
e34caace 234[[what-is-a-branch]]
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235Understanding history: What is a branch?
236~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
237
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238When we need to be precise, we will use the word "branch" to mean a line
239of development, and "branch head" (or just "head") to mean a reference
240to the most recent commit on a branch. In the example above, the branch
241head named "A" is a pointer to one particular commit, but we refer to
242the line of three commits leading up to that point as all being part of
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243"branch A".
244
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245However, when no confusion will result, we often just use the term
246"branch" both for branches and for branch heads.
d19fbc3c 247
e34caace 248[[manipulating-branches]]
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249Manipulating branches
250---------------------
251
252Creating, deleting, and modifying branches is quick and easy; here's
253a summary of the commands:
254
255git branch::
256 list all branches
257git branch <branch>::
258 create a new branch named <branch>, referencing the same
259 point in history as the current branch
260git branch <branch> <start-point>::
261 create a new branch named <branch>, referencing
262 <start-point>, which may be specified any way you like,
263 including using a branch name or a tag name
264git branch -d <branch>::
265 delete the branch <branch>; if the branch you are deleting
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266 points to a commit which is not reachable from the current
267 branch, this command will fail with a warning.
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268git branch -D <branch>::
269 even if the branch points to a commit not reachable
270 from the current branch, you may know that that commit
271 is still reachable from some other branch or tag. In that
272 case it is safe to use this command to force git to delete
273 the branch.
274git checkout <branch>::
275 make the current branch <branch>, updating the working
276 directory to reflect the version referenced by <branch>
277git checkout -b <new> <start-point>::
278 create a new branch <new> referencing <start-point>, and
279 check it out.
280
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281The special symbol "HEAD" can always be used to refer to the current
282branch. In fact, git uses a file named "HEAD" in the .git directory to
283remember which branch is current:
284
285------------------------------------------------
286$ cat .git/HEAD
287ref: refs/heads/master
288------------------------------------------------
289
25d9f3fa 290[[detached-head]]
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291Examining an old version without creating a new branch
292------------------------------------------------------
293
294The git-checkout command normally expects a branch head, but will also
295accept an arbitrary commit; for example, you can check out the commit
296referenced by a tag:
297
298------------------------------------------------
299$ git checkout v2.6.17
300Note: moving to "v2.6.17" which isn't a local branch
301If you want to create a new branch from this checkout, you may do so
302(now or later) by using -b with the checkout command again. Example:
303 git checkout -b <new_branch_name>
304HEAD is now at 427abfa... Linux v2.6.17
305------------------------------------------------
306
307The HEAD then refers to the SHA1 of the commit instead of to a branch,
308and git branch shows that you are no longer on a branch:
309
310------------------------------------------------
311$ cat .git/HEAD
312427abfa28afedffadfca9dd8b067eb6d36bac53f
953f3d6f 313$ git branch
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314* (no branch)
315 master
316------------------------------------------------
317
318In this case we say that the HEAD is "detached".
319
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320This is an easy way to check out a particular version without having to
321make up a name for the new branch. You can still create a new branch
322(or tag) for this version later if you decide to.
d19fbc3c 323
e34caace 324[[examining-remote-branches]]
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325Examining branches from a remote repository
326-------------------------------------------
327
328The "master" branch that was created at the time you cloned is a copy
329of the HEAD in the repository that you cloned from. That repository
330may also have had other branches, though, and your local repository
331keeps branches which track each of those remote branches, which you
332can view using the "-r" option to gitlink:git-branch[1]:
333
334------------------------------------------------
335$ git branch -r
336 origin/HEAD
337 origin/html
338 origin/maint
339 origin/man
340 origin/master
341 origin/next
342 origin/pu
343 origin/todo
344------------------------------------------------
345
346You cannot check out these remote-tracking branches, but you can
347examine them on a branch of your own, just as you would a tag:
348
349------------------------------------------------
350$ git checkout -b my-todo-copy origin/todo
351------------------------------------------------
352
353Note that the name "origin" is just the name that git uses by default
354to refer to the repository that you cloned from.
355
356[[how-git-stores-references]]
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357Naming branches, tags, and other references
358-------------------------------------------
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359
360Branches, remote-tracking branches, and tags are all references to
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361commits. All references are named with a slash-separated path name
362starting with "refs"; the names we've been using so far are actually
363shorthand:
d19fbc3c 364
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365 - The branch "test" is short for "refs/heads/test".
366 - The tag "v2.6.18" is short for "refs/tags/v2.6.18".
367 - "origin/master" is short for "refs/remotes/origin/master".
d19fbc3c 368
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369The full name is occasionally useful if, for example, there ever
370exists a tag and a branch with the same name.
d19fbc3c 371
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372(Newly created refs are actually stored in the .git/refs directory,
373under the path given by their name. However, for efficiency reasons
374they may also be packed together in a single file; see
375gitlink:git-pack-refs[1]).
376
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377As another useful shortcut, the "HEAD" of a repository can be referred
378to just using the name of that repository. So, for example, "origin"
379is usually a shortcut for the HEAD branch in the repository "origin".
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380
381For the complete list of paths which git checks for references, and
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382the order it uses to decide which to choose when there are multiple
383references with the same shorthand name, see the "SPECIFYING
384REVISIONS" section of gitlink:git-rev-parse[1].
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385
386[[Updating-a-repository-with-git-fetch]]
387Updating a repository with git fetch
388------------------------------------
389
390Eventually the developer cloned from will do additional work in her
391repository, creating new commits and advancing the branches to point
392at the new commits.
393
394The command "git fetch", with no arguments, will update all of the
395remote-tracking branches to the latest version found in her
396repository. It will not touch any of your own branches--not even the
397"master" branch that was created for you on clone.
398
e34caace 399[[fetching-branches]]
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400Fetching branches from other repositories
401-----------------------------------------
402
403You can also track branches from repositories other than the one you
404cloned from, using gitlink:git-remote[1]:
405
406-------------------------------------------------
407$ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git
04483524 408$ git fetch linux-nfs
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409* refs/remotes/linux-nfs/master: storing branch 'master' ...
410 commit: bf81b46
411-------------------------------------------------
412
413New remote-tracking branches will be stored under the shorthand name
414that you gave "git remote add", in this case linux-nfs:
415
416-------------------------------------------------
417$ git branch -r
418linux-nfs/master
419origin/master
420-------------------------------------------------
421
422If you run "git fetch <remote>" later, the tracking branches for the
423named <remote> will be updated.
424
425If you examine the file .git/config, you will see that git has added
426a new stanza:
427
428-------------------------------------------------
429$ cat .git/config
430...
431[remote "linux-nfs"]
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432 url = git://linux-nfs.org/pub/nfs-2.6.git
433 fetch = +refs/heads/*:refs/remotes/linux-nfs/*
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434...
435-------------------------------------------------
436
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437This is what causes git to track the remote's branches; you may modify
438or delete these configuration options by editing .git/config with a
439text editor. (See the "CONFIGURATION FILE" section of
440gitlink:git-config[1] for details.)
d5cd5de4 441
e34caace 442[[exploring-git-history]]
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443Exploring git history
444=====================
445
446Git is best thought of as a tool for storing the history of a
447collection of files. It does this by storing compressed snapshots of
1130845b 448the contents of a file hierarchy, together with "commits" which show
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449the relationships between these snapshots.
450
451Git provides extremely flexible and fast tools for exploring the
452history of a project.
453
aacd404e 454We start with one specialized tool that is useful for finding the
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455commit that introduced a bug into a project.
456
e34caace 457[[using-bisect]]
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458How to use bisect to find a regression
459--------------------------------------
460
461Suppose version 2.6.18 of your project worked, but the version at
462"master" crashes. Sometimes the best way to find the cause of such a
463regression is to perform a brute-force search through the project's
464history to find the particular commit that caused the problem. The
465gitlink:git-bisect[1] command can help you do this:
466
467-------------------------------------------------
468$ git bisect start
469$ git bisect good v2.6.18
470$ git bisect bad master
471Bisecting: 3537 revisions left to test after this
472[65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]
473-------------------------------------------------
474
475If you run "git branch" at this point, you'll see that git has
476temporarily moved you to a new branch named "bisect". This branch
477points to a commit (with commit id 65934...) that is reachable from
478v2.6.19 but not from v2.6.18. Compile and test it, and see whether
479it crashes. Assume it does crash. Then:
480
481-------------------------------------------------
482$ git bisect bad
483Bisecting: 1769 revisions left to test after this
484[7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings
485-------------------------------------------------
486
487checks out an older version. Continue like this, telling git at each
488stage whether the version it gives you is good or bad, and notice
489that the number of revisions left to test is cut approximately in
490half each time.
491
492After about 13 tests (in this case), it will output the commit id of
493the guilty commit. You can then examine the commit with
494gitlink:git-show[1], find out who wrote it, and mail them your bug
495report with the commit id. Finally, run
496
497-------------------------------------------------
498$ git bisect reset
499-------------------------------------------------
500
501to return you to the branch you were on before and delete the
502temporary "bisect" branch.
503
504Note that the version which git-bisect checks out for you at each
505point is just a suggestion, and you're free to try a different
506version if you think it would be a good idea. For example,
507occasionally you may land on a commit that broke something unrelated;
508run
509
510-------------------------------------------------
04483524 511$ git bisect visualize
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512-------------------------------------------------
513
514which will run gitk and label the commit it chose with a marker that
515says "bisect". Chose a safe-looking commit nearby, note its commit
516id, and check it out with:
517
518-------------------------------------------------
519$ git reset --hard fb47ddb2db...
520-------------------------------------------------
521
522then test, run "bisect good" or "bisect bad" as appropriate, and
523continue.
524
e34caace 525[[naming-commits]]
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526Naming commits
527--------------
528
529We have seen several ways of naming commits already:
530
d55ae921 531 - 40-hexdigit object name
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532 - branch name: refers to the commit at the head of the given
533 branch
534 - tag name: refers to the commit pointed to by the given tag
535 (we've seen branches and tags are special cases of
536 <<how-git-stores-references,references>>).
537 - HEAD: refers to the head of the current branch
538
eb6ae7f4 539There are many more; see the "SPECIFYING REVISIONS" section of the
aec053bb 540gitlink:git-rev-parse[1] man page for the complete list of ways to
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541name revisions. Some examples:
542
543-------------------------------------------------
d55ae921 544$ git show fb47ddb2 # the first few characters of the object name
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545 # are usually enough to specify it uniquely
546$ git show HEAD^ # the parent of the HEAD commit
547$ git show HEAD^^ # the grandparent
548$ git show HEAD~4 # the great-great-grandparent
549-------------------------------------------------
550
551Recall that merge commits may have more than one parent; by default,
552^ and ~ follow the first parent listed in the commit, but you can
553also choose:
554
555-------------------------------------------------
556$ git show HEAD^1 # show the first parent of HEAD
557$ git show HEAD^2 # show the second parent of HEAD
558-------------------------------------------------
559
560In addition to HEAD, there are several other special names for
561commits:
562
563Merges (to be discussed later), as well as operations such as
564git-reset, which change the currently checked-out commit, generally
565set ORIG_HEAD to the value HEAD had before the current operation.
566
567The git-fetch operation always stores the head of the last fetched
568branch in FETCH_HEAD. For example, if you run git fetch without
569specifying a local branch as the target of the operation
570
571-------------------------------------------------
572$ git fetch git://example.com/proj.git theirbranch
573-------------------------------------------------
574
575the fetched commits will still be available from FETCH_HEAD.
576
577When we discuss merges we'll also see the special name MERGE_HEAD,
578which refers to the other branch that we're merging in to the current
579branch.
580
aec053bb 581The gitlink:git-rev-parse[1] command is a low-level command that is
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582occasionally useful for translating some name for a commit to the object
583name for that commit:
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584
585-------------------------------------------------
586$ git rev-parse origin
587e05db0fd4f31dde7005f075a84f96b360d05984b
588-------------------------------------------------
589
e34caace 590[[creating-tags]]
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591Creating tags
592-------------
593
594We can also create a tag to refer to a particular commit; after
595running
596
597-------------------------------------------------
04483524 598$ git tag stable-1 1b2e1d63ff
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599-------------------------------------------------
600
601You can use stable-1 to refer to the commit 1b2e1d63ff.
602
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603This creates a "lightweight" tag. If you would also like to include a
604comment with the tag, and possibly sign it cryptographically, then you
605should create a tag object instead; see the gitlink:git-tag[1] man page
606for details.
d19fbc3c 607
e34caace 608[[browsing-revisions]]
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609Browsing revisions
610------------------
611
612The gitlink:git-log[1] command can show lists of commits. On its
613own, it shows all commits reachable from the parent commit; but you
614can also make more specific requests:
615
616-------------------------------------------------
617$ git log v2.5.. # commits since (not reachable from) v2.5
618$ git log test..master # commits reachable from master but not test
619$ git log master..test # ...reachable from test but not master
620$ git log master...test # ...reachable from either test or master,
621 # but not both
622$ git log --since="2 weeks ago" # commits from the last 2 weeks
623$ git log Makefile # commits which modify Makefile
624$ git log fs/ # ... which modify any file under fs/
625$ git log -S'foo()' # commits which add or remove any file data
626 # matching the string 'foo()'
627-------------------------------------------------
628
629And of course you can combine all of these; the following finds
630commits since v2.5 which touch the Makefile or any file under fs:
631
632-------------------------------------------------
633$ git log v2.5.. Makefile fs/
634-------------------------------------------------
635
636You can also ask git log to show patches:
637
638-------------------------------------------------
639$ git log -p
640-------------------------------------------------
641
642See the "--pretty" option in the gitlink:git-log[1] man page for more
643display options.
644
645Note that git log starts with the most recent commit and works
646backwards through the parents; however, since git history can contain
3dff5379 647multiple independent lines of development, the particular order that
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648commits are listed in may be somewhat arbitrary.
649
e34caace 650[[generating-diffs]]
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651Generating diffs
652----------------
653
654You can generate diffs between any two versions using
655gitlink:git-diff[1]:
656
657-------------------------------------------------
658$ git diff master..test
659-------------------------------------------------
660
661Sometimes what you want instead is a set of patches:
662
663-------------------------------------------------
664$ git format-patch master..test
665-------------------------------------------------
666
667will generate a file with a patch for each commit reachable from test
668but not from master. Note that if master also has commits which are
669not reachable from test, then the combined result of these patches
670will not be the same as the diff produced by the git-diff example.
671
e34caace 672[[viewing-old-file-versions]]
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673Viewing old file versions
674-------------------------
675
676You can always view an old version of a file by just checking out the
677correct revision first. But sometimes it is more convenient to be
678able to view an old version of a single file without checking
679anything out; this command does that:
680
681-------------------------------------------------
682$ git show v2.5:fs/locks.c
683-------------------------------------------------
684
685Before the colon may be anything that names a commit, and after it
686may be any path to a file tracked by git.
687
e34caace 688[[history-examples]]
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689Examples
690--------
691
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692[[counting-commits-on-a-branch]]
693Counting the number of commits on a branch
694~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
695
696Suppose you want to know how many commits you've made on "mybranch"
697since it diverged from "origin":
698
699-------------------------------------------------
700$ git log --pretty=oneline origin..mybranch | wc -l
701-------------------------------------------------
702
703Alternatively, you may often see this sort of thing done with the
704lower-level command gitlink:git-rev-list[1], which just lists the SHA1's
705of all the given commits:
706
707-------------------------------------------------
708$ git rev-list origin..mybranch | wc -l
709-------------------------------------------------
710
e34caace 711[[checking-for-equal-branches]]
aec053bb 712Check whether two branches point at the same history
2f99710c 713~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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714
715Suppose you want to check whether two branches point at the same point
716in history.
717
718-------------------------------------------------
719$ git diff origin..master
720-------------------------------------------------
721
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722will tell you whether the contents of the project are the same at the
723two branches; in theory, however, it's possible that the same project
724contents could have been arrived at by two different historical
d55ae921 725routes. You could compare the object names:
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726
727-------------------------------------------------
728$ git rev-list origin
729e05db0fd4f31dde7005f075a84f96b360d05984b
730$ git rev-list master
731e05db0fd4f31dde7005f075a84f96b360d05984b
732-------------------------------------------------
733
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734Or you could recall that the ... operator selects all commits
735contained reachable from either one reference or the other but not
736both: so
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737
738-------------------------------------------------
739$ git log origin...master
740-------------------------------------------------
741
742will return no commits when the two branches are equal.
743
e34caace 744[[finding-tagged-descendants]]
b181d57f
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745Find first tagged version including a given fix
746~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
aec053bb 747
69f7ad73
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748Suppose you know that the commit e05db0fd fixed a certain problem.
749You'd like to find the earliest tagged release that contains that
750fix.
751
752Of course, there may be more than one answer--if the history branched
753after commit e05db0fd, then there could be multiple "earliest" tagged
754releases.
755
756You could just visually inspect the commits since e05db0fd:
757
758-------------------------------------------------
759$ gitk e05db0fd..
760-------------------------------------------------
761
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762Or you can use gitlink:git-name-rev[1], which will give the commit a
763name based on any tag it finds pointing to one of the commit's
764descendants:
765
766-------------------------------------------------
04483524 767$ git name-rev --tags e05db0fd
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768e05db0fd tags/v1.5.0-rc1^0~23
769-------------------------------------------------
770
771The gitlink:git-describe[1] command does the opposite, naming the
772revision using a tag on which the given commit is based:
773
774-------------------------------------------------
775$ git describe e05db0fd
04483524 776v1.5.0-rc0-260-ge05db0f
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777-------------------------------------------------
778
779but that may sometimes help you guess which tags might come after the
780given commit.
781
782If you just want to verify whether a given tagged version contains a
783given commit, you could use gitlink:git-merge-base[1]:
784
785-------------------------------------------------
786$ git merge-base e05db0fd v1.5.0-rc1
787e05db0fd4f31dde7005f075a84f96b360d05984b
788-------------------------------------------------
789
790The merge-base command finds a common ancestor of the given commits,
791and always returns one or the other in the case where one is a
792descendant of the other; so the above output shows that e05db0fd
793actually is an ancestor of v1.5.0-rc1.
794
795Alternatively, note that
796
797-------------------------------------------------
4a7979ca 798$ git log v1.5.0-rc1..e05db0fd
b181d57f
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799-------------------------------------------------
800
4a7979ca 801will produce empty output if and only if v1.5.0-rc1 includes e05db0fd,
b181d57f 802because it outputs only commits that are not reachable from v1.5.0-rc1.
aec053bb 803
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804As yet another alternative, the gitlink:git-show-branch[1] command lists
805the commits reachable from its arguments with a display on the left-hand
806side that indicates which arguments that commit is reachable from. So,
807you can run something like
808
809-------------------------------------------------
810$ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2
811! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
812available
813 ! [v1.5.0-rc0] GIT v1.5.0 preview
814 ! [v1.5.0-rc1] GIT v1.5.0-rc1
815 ! [v1.5.0-rc2] GIT v1.5.0-rc2
816...
817-------------------------------------------------
818
819then search for a line that looks like
820
821-------------------------------------------------
822+ ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
823available
824-------------------------------------------------
825
826Which shows that e05db0fd is reachable from itself, from v1.5.0-rc1, and
827from v1.5.0-rc2, but not from v1.5.0-rc0.
828
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829[[showing-commits-unique-to-a-branch]]
830Showing commits unique to a given branch
831~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4a7979ca 832
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833Suppose you would like to see all the commits reachable from the branch
834head named "master" but not from any other head in your repository.
d19fbc3c 835
629d9f78
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836We can list all the heads in this repository with
837gitlink:git-show-ref[1]:
d19fbc3c 838
629d9f78
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839-------------------------------------------------
840$ git show-ref --heads
841bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial
842db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint
843a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master
84424dbc180ea14dc1aebe09f14c8ecf32010690627 refs/heads/tutorial-2
8451e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes
846-------------------------------------------------
d19fbc3c 847
629d9f78
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848We can get just the branch-head names, and remove "master", with
849the help of the standard utilities cut and grep:
850
851-------------------------------------------------
852$ git show-ref --heads | cut -d' ' -f2 | grep -v '^refs/heads/master'
853refs/heads/core-tutorial
854refs/heads/maint
855refs/heads/tutorial-2
856refs/heads/tutorial-fixes
857-------------------------------------------------
858
859And then we can ask to see all the commits reachable from master
860but not from these other heads:
861
862-------------------------------------------------
863$ gitk master --not $( git show-ref --heads | cut -d' ' -f2 |
864 grep -v '^refs/heads/master' )
865-------------------------------------------------
866
867Obviously, endless variations are possible; for example, to see all
868commits reachable from some head but not from any tag in the repository:
869
870-------------------------------------------------
c78974f7 871$ gitk $( git show-ref --heads ) --not $( git show-ref --tags )
629d9f78
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872-------------------------------------------------
873
874(See gitlink:git-rev-parse[1] for explanations of commit-selecting
875syntax such as `--not`.)
876
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877[[making-a-release]]
878Creating a changelog and tarball for a software release
879~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
880
881The gitlink:git-archive[1] command can create a tar or zip archive from
882any version of a project; for example:
883
884-------------------------------------------------
885$ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz
886-------------------------------------------------
887
888will use HEAD to produce a tar archive in which each filename is
ccd71866 889preceded by "project/".
82c8bf28
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890
891If you're releasing a new version of a software project, you may want
892to simultaneously make a changelog to include in the release
893announcement.
894
895Linus Torvalds, for example, makes new kernel releases by tagging them,
896then running:
897
898-------------------------------------------------
899$ release-script 2.6.12 2.6.13-rc6 2.6.13-rc7
900-------------------------------------------------
901
902where release-script is a shell script that looks like:
903
904-------------------------------------------------
905#!/bin/sh
906stable="$1"
907last="$2"
908new="$3"
909echo "# git tag v$new"
910echo "git archive --prefix=linux-$new/ v$new | gzip -9 > ../linux-$new.tar.gz"
911echo "git diff v$stable v$new | gzip -9 > ../patch-$new.gz"
912echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new"
913echo "git shortlog --no-merges v$new ^v$last > ../ShortLog"
914echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new"
915-------------------------------------------------
916
917and then he just cut-and-pastes the output commands after verifying that
918they look OK.
4a7979ca 919
8ceca74a 920[[Finding-comments-with-given-content]]
187b0d80 921Finding commits referencing a file with given content
d5821de2 922~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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923
924Somebody hands you a copy of a file, and asks which commits modified a
925file such that it contained the given content either before or after the
926commit. You can find out with this:
927
928-------------------------------------------------
170c0438 929$ git log --raw --abbrev=40 --pretty=oneline -- filename |
187b0d80
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930 grep -B 1 `git hash-object filename`
931-------------------------------------------------
932
933Figuring out why this works is left as an exercise to the (advanced)
934student. The gitlink:git-log[1], gitlink:git-diff-tree[1], and
935gitlink:git-hash-object[1] man pages may prove helpful.
936
e34caace 937[[Developing-with-git]]
d19fbc3c
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938Developing with git
939===================
940
e34caace 941[[telling-git-your-name]]
d19fbc3c
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942Telling git your name
943---------------------
944
945Before creating any commits, you should introduce yourself to git. The
58c19d1f
BF
946easiest way to do so is to make sure the following lines appear in a
947file named .gitconfig in your home directory:
d19fbc3c
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948
949------------------------------------------------
d19fbc3c
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950[user]
951 name = Your Name Comes Here
952 email = you@yourdomain.example.com
d19fbc3c
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953------------------------------------------------
954
fc90c536
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955(See the "CONFIGURATION FILE" section of gitlink:git-config[1] for
956details on the configuration file.)
957
d19fbc3c 958
e34caace 959[[creating-a-new-repository]]
d19fbc3c
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960Creating a new repository
961-------------------------
962
963Creating a new repository from scratch is very easy:
964
965-------------------------------------------------
966$ mkdir project
967$ cd project
f1d2b477 968$ git init
d19fbc3c
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969-------------------------------------------------
970
971If you have some initial content (say, a tarball):
972
973-------------------------------------------------
974$ tar -xzvf project.tar.gz
975$ cd project
f1d2b477 976$ git init
d19fbc3c
BF
977$ git add . # include everything below ./ in the first commit:
978$ git commit
979-------------------------------------------------
980
981[[how-to-make-a-commit]]
ae25c67a 982How to make a commit
d19fbc3c
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983--------------------
984
985Creating a new commit takes three steps:
986
987 1. Making some changes to the working directory using your
988 favorite editor.
989 2. Telling git about your changes.
990 3. Creating the commit using the content you told git about
991 in step 2.
992
993In practice, you can interleave and repeat steps 1 and 2 as many
994times as you want: in order to keep track of what you want committed
995at step 3, git maintains a snapshot of the tree's contents in a
996special staging area called "the index."
997
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998At the beginning, the content of the index will be identical to
999that of the HEAD. The command "git diff --cached", which shows
1000the difference between the HEAD and the index, should therefore
1001produce no output at that point.
eb6ae7f4 1002
d19fbc3c
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1003Modifying the index is easy:
1004
1005To update the index with the new contents of a modified file, use
1006
1007-------------------------------------------------
1008$ git add path/to/file
1009-------------------------------------------------
1010
1011To add the contents of a new file to the index, use
1012
1013-------------------------------------------------
1014$ git add path/to/file
1015-------------------------------------------------
1016
eb6ae7f4 1017To remove a file from the index and from the working tree,
d19fbc3c
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1018
1019-------------------------------------------------
1020$ git rm path/to/file
1021-------------------------------------------------
1022
1023After each step you can verify that
1024
1025-------------------------------------------------
1026$ git diff --cached
1027-------------------------------------------------
1028
1029always shows the difference between the HEAD and the index file--this
1030is what you'd commit if you created the commit now--and that
1031
1032-------------------------------------------------
1033$ git diff
1034-------------------------------------------------
1035
1036shows the difference between the working tree and the index file.
1037
1038Note that "git add" always adds just the current contents of a file
1039to the index; further changes to the same file will be ignored unless
1040you run git-add on the file again.
1041
1042When you're ready, just run
1043
1044-------------------------------------------------
1045$ git commit
1046-------------------------------------------------
1047
1048and git will prompt you for a commit message and then create the new
3dff5379 1049commit. Check to make sure it looks like what you expected with
d19fbc3c
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1050
1051-------------------------------------------------
1052$ git show
1053-------------------------------------------------
1054
1055As a special shortcut,
a6080a0a 1056
d19fbc3c
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1057-------------------------------------------------
1058$ git commit -a
1059-------------------------------------------------
1060
1061will update the index with any files that you've modified or removed
1062and create a commit, all in one step.
1063
1064A number of commands are useful for keeping track of what you're
1065about to commit:
1066
1067-------------------------------------------------
1068$ git diff --cached # difference between HEAD and the index; what
1130845b 1069 # would be committed if you ran "commit" now.
d19fbc3c
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1070$ git diff # difference between the index file and your
1071 # working directory; changes that would not
1072 # be included if you ran "commit" now.
c64415e2
BF
1073$ git diff HEAD # difference between HEAD and working tree; what
1074 # would be committed if you ran "commit -a" now.
d19fbc3c
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1075$ git status # a brief per-file summary of the above.
1076-------------------------------------------------
1077
407c0c87
BF
1078You can also use gitlink:git-gui[1] to create commits, view changes in
1079the index and the working tree files, and individually select diff hunks
1080for inclusion in the index (by right-clicking on the diff hunk and
1081choosing "Stage Hunk For Commit").
1082
e34caace 1083[[creating-good-commit-messages]]
ae25c67a 1084Creating good commit messages
d19fbc3c
BF
1085-----------------------------
1086
1087Though not required, it's a good idea to begin the commit message
1088with a single short (less than 50 character) line summarizing the
1089change, followed by a blank line and then a more thorough
1090description. Tools that turn commits into email, for example, use
1091the first line on the Subject line and the rest of the commit in the
1092body.
1093
2dc53617
JH
1094[[ignoring-files]]
1095Ignoring files
1096--------------
1097
1098A project will often generate files that you do 'not' want to track with git.
1099This typically includes files generated by a build process or temporary
1100backup files made by your editor. Of course, 'not' tracking files with git
1101is just a matter of 'not' calling "`git add`" on them. But it quickly becomes
1102annoying to have these untracked files lying around; e.g. they make
1103"`git add .`" and "`git commit -a`" practically useless, and they keep
464a8a7a 1104showing up in the output of "`git status`".
2dc53617 1105
464a8a7a
BF
1106You can tell git to ignore certain files by creating a file called .gitignore
1107in the top level of your working directory, with contents such as:
2dc53617
JH
1108
1109-------------------------------------------------
1110# Lines starting with '#' are considered comments.
464a8a7a 1111# Ignore any file named foo.txt.
2dc53617
JH
1112foo.txt
1113# Ignore (generated) html files,
1114*.html
1115# except foo.html which is maintained by hand.
1116!foo.html
1117# Ignore objects and archives.
1118*.[oa]
1119-------------------------------------------------
1120
464a8a7a
BF
1121See gitlink:gitignore[5] for a detailed explanation of the syntax. You can
1122also place .gitignore files in other directories in your working tree, and they
1123will apply to those directories and their subdirectories. The `.gitignore`
1124files can be added to your repository like any other files (just run `git add
1125.gitignore` and `git commit`, as usual), which is convenient when the exclude
1126patterns (such as patterns matching build output files) would also make sense
1127for other users who clone your repository.
1128
1129If you wish the exclude patterns to affect only certain repositories
1130(instead of every repository for a given project), you may instead put
1131them in a file in your repository named .git/info/exclude, or in any file
1132specified by the `core.excludesfile` configuration variable. Some git
1133commands can also take exclude patterns directly on the command line.
1134See gitlink:gitignore[5] for the details.
2dc53617 1135
e34caace 1136[[how-to-merge]]
ae25c67a 1137How to merge
d19fbc3c
BF
1138------------
1139
1140You can rejoin two diverging branches of development using
1141gitlink:git-merge[1]:
1142
1143-------------------------------------------------
1144$ git merge branchname
1145-------------------------------------------------
1146
1147merges the development in the branch "branchname" into the current
1148branch. If there are conflicts--for example, if the same file is
1149modified in two different ways in the remote branch and the local
1150branch--then you are warned; the output may look something like this:
1151
1152-------------------------------------------------
fabbd8f6
BF
1153$ git merge next
1154 100% (4/4) done
1155Auto-merged file.txt
d19fbc3c
BF
1156CONFLICT (content): Merge conflict in file.txt
1157Automatic merge failed; fix conflicts and then commit the result.
1158-------------------------------------------------
1159
1160Conflict markers are left in the problematic files, and after
1161you resolve the conflicts manually, you can update the index
1162with the contents and run git commit, as you normally would when
1163creating a new file.
1164
1165If you examine the resulting commit using gitk, you will see that it
1166has two parents, one pointing to the top of the current branch, and
1167one to the top of the other branch.
1168
d19fbc3c
BF
1169[[resolving-a-merge]]
1170Resolving a merge
1171-----------------
1172
1173When a merge isn't resolved automatically, git leaves the index and
1174the working tree in a special state that gives you all the
1175information you need to help resolve the merge.
1176
1177Files with conflicts are marked specially in the index, so until you
ef561ac7
BF
1178resolve the problem and update the index, gitlink:git-commit[1] will
1179fail:
d19fbc3c
BF
1180
1181-------------------------------------------------
1182$ git commit
1183file.txt: needs merge
1184-------------------------------------------------
1185
ef561ac7
BF
1186Also, gitlink:git-status[1] will list those files as "unmerged", and the
1187files with conflicts will have conflict markers added, like this:
1188
1189-------------------------------------------------
1190<<<<<<< HEAD:file.txt
1191Hello world
1192=======
1193Goodbye
1194>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1195-------------------------------------------------
1196
1197All you need to do is edit the files to resolve the conflicts, and then
1198
1199-------------------------------------------------
1200$ git add file.txt
1201$ git commit
1202-------------------------------------------------
1203
1204Note that the commit message will already be filled in for you with
1205some information about the merge. Normally you can just use this
1206default message unchanged, but you may add additional commentary of
1207your own if desired.
1208
1209The above is all you need to know to resolve a simple merge. But git
1210also provides more information to help resolve conflicts:
1211
e34caace 1212[[conflict-resolution]]
ef561ac7
BF
1213Getting conflict-resolution help during a merge
1214~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
BF
1215
1216All of the changes that git was able to merge automatically are
1217already added to the index file, so gitlink:git-diff[1] shows only
ef561ac7 1218the conflicts. It uses an unusual syntax:
d19fbc3c
BF
1219
1220-------------------------------------------------
1221$ git diff
1222diff --cc file.txt
1223index 802992c,2b60207..0000000
1224--- a/file.txt
1225+++ b/file.txt
1226@@@ -1,1 -1,1 +1,5 @@@
1227++<<<<<<< HEAD:file.txt
1228 +Hello world
1229++=======
1230+ Goodbye
1231++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1232-------------------------------------------------
1233
1130845b 1234Recall that the commit which will be committed after we resolve this
d19fbc3c
BF
1235conflict will have two parents instead of the usual one: one parent
1236will be HEAD, the tip of the current branch; the other will be the
1237tip of the other branch, which is stored temporarily in MERGE_HEAD.
1238
ef561ac7
BF
1239During the merge, the index holds three versions of each file. Each of
1240these three "file stages" represents a different version of the file:
1241
1242-------------------------------------------------
1243$ git show :1:file.txt # the file in a common ancestor of both branches
1244$ git show :2:file.txt # the version from HEAD, but including any
1245 # nonconflicting changes from MERGE_HEAD
1246$ git show :3:file.txt # the version from MERGE_HEAD, but including any
1247 # nonconflicting changes from HEAD.
1248-------------------------------------------------
1249
1250Since the stage 2 and stage 3 versions have already been updated with
1251nonconflicting changes, the only remaining differences between them are
1252the important ones; thus gitlink:git-diff[1] can use the information in
1253the index to show only those conflicts.
1254
1255The diff above shows the differences between the working-tree version of
1256file.txt and the stage 2 and stage 3 versions. So instead of preceding
1257each line by a single "+" or "-", it now uses two columns: the first
1258column is used for differences between the first parent and the working
1259directory copy, and the second for differences between the second parent
1260and the working directory copy. (See the "COMBINED DIFF FORMAT" section
1261of gitlink:git-diff-files[1] for a details of the format.)
1262
1263After resolving the conflict in the obvious way (but before updating the
1264index), the diff will look like:
d19fbc3c
BF
1265
1266-------------------------------------------------
1267$ git diff
1268diff --cc file.txt
1269index 802992c,2b60207..0000000
1270--- a/file.txt
1271+++ b/file.txt
1272@@@ -1,1 -1,1 +1,1 @@@
1273- Hello world
1274 -Goodbye
1275++Goodbye world
1276-------------------------------------------------
1277
1278This shows that our resolved version deleted "Hello world" from the
1279first parent, deleted "Goodbye" from the second parent, and added
1280"Goodbye world", which was previously absent from both.
1281
ef561ac7
BF
1282Some special diff options allow diffing the working directory against
1283any of these stages:
1284
1285-------------------------------------------------
1286$ git diff -1 file.txt # diff against stage 1
1287$ git diff --base file.txt # same as the above
1288$ git diff -2 file.txt # diff against stage 2
1289$ git diff --ours file.txt # same as the above
1290$ git diff -3 file.txt # diff against stage 3
1291$ git diff --theirs file.txt # same as the above.
1292-------------------------------------------------
1293
1294The gitlink:git-log[1] and gitk[1] commands also provide special help
1295for merges:
d19fbc3c
BF
1296
1297-------------------------------------------------
1298$ git log --merge
ef561ac7 1299$ gitk --merge
d19fbc3c
BF
1300-------------------------------------------------
1301
ef561ac7
BF
1302These will display all commits which exist only on HEAD or on
1303MERGE_HEAD, and which touch an unmerged file.
d19fbc3c 1304
61d72564 1305You may also use gitlink:git-mergetool[1], which lets you merge the
c64415e2
BF
1306unmerged files using external tools such as emacs or kdiff3.
1307
ef561ac7 1308Each time you resolve the conflicts in a file and update the index:
d19fbc3c
BF
1309
1310-------------------------------------------------
1311$ git add file.txt
d19fbc3c
BF
1312-------------------------------------------------
1313
ef561ac7
BF
1314the different stages of that file will be "collapsed", after which
1315git-diff will (by default) no longer show diffs for that file.
d19fbc3c
BF
1316
1317[[undoing-a-merge]]
ae25c67a 1318Undoing a merge
d19fbc3c
BF
1319---------------
1320
1321If you get stuck and decide to just give up and throw the whole mess
1322away, you can always return to the pre-merge state with
1323
1324-------------------------------------------------
1325$ git reset --hard HEAD
1326-------------------------------------------------
1327
1130845b 1328Or, if you've already committed the merge that you want to throw away,
d19fbc3c
BF
1329
1330-------------------------------------------------
1c73bb0e 1331$ git reset --hard ORIG_HEAD
d19fbc3c
BF
1332-------------------------------------------------
1333
1334However, this last command can be dangerous in some cases--never
1335throw away a commit you have already committed if that commit may
1336itself have been merged into another branch, as doing so may confuse
1337further merges.
1338
e34caace 1339[[fast-forwards]]
d19fbc3c
BF
1340Fast-forward merges
1341-------------------
1342
1343There is one special case not mentioned above, which is treated
1344differently. Normally, a merge results in a merge commit, with two
1345parents, one pointing at each of the two lines of development that
1346were merged.
1347
59723040
BF
1348However, if the current branch is a descendant of the other--so every
1349commit present in the one is already contained in the other--then git
1350just performs a "fast forward"; the head of the current branch is moved
1351forward to point at the head of the merged-in branch, without any new
1352commits being created.
d19fbc3c 1353
e34caace 1354[[fixing-mistakes]]
b684f830
BF
1355Fixing mistakes
1356---------------
1357
1358If you've messed up the working tree, but haven't yet committed your
1359mistake, you can return the entire working tree to the last committed
1360state with
1361
1362-------------------------------------------------
1363$ git reset --hard HEAD
1364-------------------------------------------------
1365
1366If you make a commit that you later wish you hadn't, there are two
1367fundamentally different ways to fix the problem:
1368
1369 1. You can create a new commit that undoes whatever was done
1370 by the previous commit. This is the correct thing if your
1371 mistake has already been made public.
1372
1373 2. You can go back and modify the old commit. You should
1374 never do this if you have already made the history public;
1375 git does not normally expect the "history" of a project to
1376 change, and cannot correctly perform repeated merges from
1377 a branch that has had its history changed.
1378
e34caace 1379[[reverting-a-commit]]
b684f830
BF
1380Fixing a mistake with a new commit
1381~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1382
1383Creating a new commit that reverts an earlier change is very easy;
1384just pass the gitlink:git-revert[1] command a reference to the bad
1385commit; for example, to revert the most recent commit:
1386
1387-------------------------------------------------
1388$ git revert HEAD
1389-------------------------------------------------
1390
1391This will create a new commit which undoes the change in HEAD. You
1392will be given a chance to edit the commit message for the new commit.
1393
1394You can also revert an earlier change, for example, the next-to-last:
1395
1396-------------------------------------------------
1397$ git revert HEAD^
1398-------------------------------------------------
1399
1400In this case git will attempt to undo the old change while leaving
1401intact any changes made since then. If more recent changes overlap
1402with the changes to be reverted, then you will be asked to fix
1403conflicts manually, just as in the case of <<resolving-a-merge,
1404resolving a merge>>.
1405
365aa199 1406[[fixing-a-mistake-by-editing-history]]
b684f830
BF
1407Fixing a mistake by editing history
1408~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1409
1410If the problematic commit is the most recent commit, and you have not
1411yet made that commit public, then you may just
1412<<undoing-a-merge,destroy it using git-reset>>.
1413
1414Alternatively, you
1415can edit the working directory and update the index to fix your
1416mistake, just as if you were going to <<how-to-make-a-commit,create a
1417new commit>>, then run
1418
1419-------------------------------------------------
1420$ git commit --amend
1421-------------------------------------------------
1422
1423which will replace the old commit by a new commit incorporating your
1424changes, giving you a chance to edit the old commit message first.
1425
1426Again, you should never do this to a commit that may already have
1427been merged into another branch; use gitlink:git-revert[1] instead in
1428that case.
1429
1430It is also possible to edit commits further back in the history, but
1431this is an advanced topic to be left for
1432<<cleaning-up-history,another chapter>>.
1433
e34caace 1434[[checkout-of-path]]
b684f830
BF
1435Checking out an old version of a file
1436~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1437
1438In the process of undoing a previous bad change, you may find it
1439useful to check out an older version of a particular file using
1440gitlink:git-checkout[1]. We've used git checkout before to switch
1441branches, but it has quite different behavior if it is given a path
1442name: the command
1443
1444-------------------------------------------------
1445$ git checkout HEAD^ path/to/file
1446-------------------------------------------------
1447
1448replaces path/to/file by the contents it had in the commit HEAD^, and
1449also updates the index to match. It does not change branches.
1450
1451If you just want to look at an old version of the file, without
1452modifying the working directory, you can do that with
1453gitlink:git-show[1]:
1454
1455-------------------------------------------------
ed4eb0d8 1456$ git show HEAD^:path/to/file
b684f830
BF
1457-------------------------------------------------
1458
1459which will display the given version of the file.
1460
7a7cc594
JH
1461[[interrupted-work]]
1462Temporarily setting aside work in progress
1463~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1464
1465While you are in the middle of working on something complicated, you
1466find an unrelated but obvious and trivial bug. You would like to fix it
1467before continuing. You can use gitlink:git-stash[1] to save the current
1468state of your work, and after fixing the bug (or, optionally after doing
1469so on a different branch and then coming back), unstash the
1470work-in-progress changes.
1471
1472------------------------------------------------
1473$ git stash "work in progress for foo feature"
1474------------------------------------------------
1475
1476This command will save your changes away to the `stash`, and
1477reset your working tree and the index to match the tip of your
1478current branch. Then you can make your fix as usual.
1479
1480------------------------------------------------
1481... edit and test ...
1482$ git commit -a -m "blorpl: typofix"
1483------------------------------------------------
1484
1485After that, you can go back to what you were working on with
1486`git stash apply`:
1487
1488------------------------------------------------
1489$ git stash apply
1490------------------------------------------------
1491
1492
e34caace 1493[[ensuring-good-performance]]
d19fbc3c
BF
1494Ensuring good performance
1495-------------------------
1496
1497On large repositories, git depends on compression to keep the history
1498information from taking up to much space on disk or in memory.
1499
1500This compression is not performed automatically. Therefore you
17217090 1501should occasionally run gitlink:git-gc[1]:
d19fbc3c
BF
1502
1503-------------------------------------------------
1504$ git gc
1505-------------------------------------------------
1506
17217090
BF
1507to recompress the archive. This can be very time-consuming, so
1508you may prefer to run git-gc when you are not doing other work.
d19fbc3c 1509
e34caace
BF
1510
1511[[ensuring-reliability]]
11e016a3
BF
1512Ensuring reliability
1513--------------------
1514
e34caace 1515[[checking-for-corruption]]
11e016a3
BF
1516Checking the repository for corruption
1517~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1518
1191ee18
BF
1519The gitlink:git-fsck[1] command runs a number of self-consistency checks
1520on the repository, and reports on any problems. This may take some
21dcb3b7
BF
1521time. The most common warning by far is about "dangling" objects:
1522
1523-------------------------------------------------
04e50e94 1524$ git fsck
21dcb3b7
BF
1525dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1526dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1527dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1528dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb
1529dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f
1530dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e
1531dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085
1532dangling tree b24c2473f1fd3d91352a624795be026d64c8841f
1533...
1534-------------------------------------------------
1535
59723040 1536Dangling objects are not a problem. At worst they may take up a little
54782859
AP
1537extra disk space. They can sometimes provide a last-resort method for
1538recovering lost work--see <<dangling-objects>> for details. However, if
1539you wish, you can remove them with gitlink:git-prune[1] or the --prune
1191ee18 1540option to gitlink:git-gc[1]:
21dcb3b7
BF
1541
1542-------------------------------------------------
1543$ git gc --prune
1544-------------------------------------------------
1545
1191ee18
BF
1546This may be time-consuming. Unlike most other git operations (including
1547git-gc when run without any options), it is not safe to prune while
1548other git operations are in progress in the same repository.
21dcb3b7 1549
e34caace 1550[[recovering-lost-changes]]
11e016a3
BF
1551Recovering lost changes
1552~~~~~~~~~~~~~~~~~~~~~~~
1553
e34caace 1554[[reflogs]]
559e4d7a
BF
1555Reflogs
1556^^^^^^^
1557
1558Say you modify a branch with gitlink:git-reset[1] --hard, and then
1559realize that the branch was the only reference you had to that point in
1560history.
1561
1562Fortunately, git also keeps a log, called a "reflog", of all the
1563previous values of each branch. So in this case you can still find the
a6080a0a 1564old history using, for example,
559e4d7a
BF
1565
1566-------------------------------------------------
1567$ git log master@{1}
1568-------------------------------------------------
1569
1570This lists the commits reachable from the previous version of the head.
1571This syntax can be used to with any git command that accepts a commit,
1572not just with git log. Some other examples:
1573
1574-------------------------------------------------
1575$ git show master@{2} # See where the branch pointed 2,
1576$ git show master@{3} # 3, ... changes ago.
1577$ gitk master@{yesterday} # See where it pointed yesterday,
1578$ gitk master@{"1 week ago"} # ... or last week
953f3d6f
BF
1579$ git log --walk-reflogs master # show reflog entries for master
1580-------------------------------------------------
1581
1582A separate reflog is kept for the HEAD, so
1583
1584-------------------------------------------------
1585$ git show HEAD@{"1 week ago"}
559e4d7a
BF
1586-------------------------------------------------
1587
953f3d6f
BF
1588will show what HEAD pointed to one week ago, not what the current branch
1589pointed to one week ago. This allows you to see the history of what
1590you've checked out.
1591
559e4d7a 1592The reflogs are kept by default for 30 days, after which they may be
036be17e 1593pruned. See gitlink:git-reflog[1] and gitlink:git-gc[1] to learn
559e4d7a
BF
1594how to control this pruning, and see the "SPECIFYING REVISIONS"
1595section of gitlink:git-rev-parse[1] for details.
1596
1597Note that the reflog history is very different from normal git history.
1598While normal history is shared by every repository that works on the
1599same project, the reflog history is not shared: it tells you only about
1600how the branches in your local repository have changed over time.
1601
59723040 1602[[dangling-object-recovery]]
559e4d7a
BF
1603Examining dangling objects
1604^^^^^^^^^^^^^^^^^^^^^^^^^^
1605
59723040
BF
1606In some situations the reflog may not be able to save you. For example,
1607suppose you delete a branch, then realize you need the history it
1608contained. The reflog is also deleted; however, if you have not yet
1609pruned the repository, then you may still be able to find the lost
1610commits in the dangling objects that git-fsck reports. See
1611<<dangling-objects>> for the details.
559e4d7a
BF
1612
1613-------------------------------------------------
1614$ git fsck
1615dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1616dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1617dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1618...
1619-------------------------------------------------
1620
aacd404e 1621You can examine
559e4d7a
BF
1622one of those dangling commits with, for example,
1623
1624------------------------------------------------
1625$ gitk 7281251ddd --not --all
1626------------------------------------------------
1627
1628which does what it sounds like: it says that you want to see the commit
1629history that is described by the dangling commit(s), but not the
1630history that is described by all your existing branches and tags. Thus
1631you get exactly the history reachable from that commit that is lost.
1632(And notice that it might not be just one commit: we only report the
1633"tip of the line" as being dangling, but there might be a whole deep
79c96c57 1634and complex commit history that was dropped.)
559e4d7a
BF
1635
1636If you decide you want the history back, you can always create a new
1637reference pointing to it, for example, a new branch:
1638
1639------------------------------------------------
a6080a0a 1640$ git branch recovered-branch 7281251ddd
559e4d7a
BF
1641------------------------------------------------
1642
59723040
BF
1643Other types of dangling objects (blobs and trees) are also possible, and
1644dangling objects can arise in other situations.
1645
11e016a3 1646
e34caace 1647[[sharing-development]]
d19fbc3c 1648Sharing development with others
b684f830 1649===============================
d19fbc3c
BF
1650
1651[[getting-updates-with-git-pull]]
1652Getting updates with git pull
b684f830 1653-----------------------------
d19fbc3c
BF
1654
1655After you clone a repository and make a few changes of your own, you
1656may wish to check the original repository for updates and merge them
1657into your own work.
1658
1659We have already seen <<Updating-a-repository-with-git-fetch,how to
1660keep remote tracking branches up to date>> with gitlink:git-fetch[1],
1661and how to merge two branches. So you can merge in changes from the
1662original repository's master branch with:
1663
1664-------------------------------------------------
1665$ git fetch
1666$ git merge origin/master
1667-------------------------------------------------
1668
1669However, the gitlink:git-pull[1] command provides a way to do this in
1670one step:
1671
1672-------------------------------------------------
1673$ git pull origin master
1674-------------------------------------------------
1675
0eb4f7cd
BF
1676In fact, if you have "master" checked out, then by default "git pull"
1677merges from the HEAD branch of the origin repository. So often you can
1678accomplish the above with just a simple
d19fbc3c
BF
1679
1680-------------------------------------------------
1681$ git pull
1682-------------------------------------------------
1683
0eb4f7cd
BF
1684More generally, a branch that is created from a remote branch will pull
1685by default from that branch. See the descriptions of the
1686branch.<name>.remote and branch.<name>.merge options in
1687gitlink:git-config[1], and the discussion of the --track option in
1688gitlink:git-checkout[1], to learn how to control these defaults.
d19fbc3c
BF
1689
1690In addition to saving you keystrokes, "git pull" also helps you by
1691producing a default commit message documenting the branch and
1692repository that you pulled from.
1693
1694(But note that no such commit will be created in the case of a
1695<<fast-forwards,fast forward>>; instead, your branch will just be
79c96c57 1696updated to point to the latest commit from the upstream branch.)
d19fbc3c 1697
1191ee18
BF
1698The git-pull command can also be given "." as the "remote" repository,
1699in which case it just merges in a branch from the current repository; so
4c63ff45
BF
1700the commands
1701
1702-------------------------------------------------
1703$ git pull . branch
1704$ git merge branch
1705-------------------------------------------------
1706
1707are roughly equivalent. The former is actually very commonly used.
1708
e34caace 1709[[submitting-patches]]
d19fbc3c 1710Submitting patches to a project
b684f830 1711-------------------------------
d19fbc3c
BF
1712
1713If you just have a few changes, the simplest way to submit them may
1714just be to send them as patches in email:
1715
036be17e 1716First, use gitlink:git-format-patch[1]; for example:
d19fbc3c
BF
1717
1718-------------------------------------------------
eb6ae7f4 1719$ git format-patch origin
d19fbc3c
BF
1720-------------------------------------------------
1721
1722will produce a numbered series of files in the current directory, one
1723for each patch in the current branch but not in origin/HEAD.
1724
1725You can then import these into your mail client and send them by
1726hand. However, if you have a lot to send at once, you may prefer to
1727use the gitlink:git-send-email[1] script to automate the process.
1728Consult the mailing list for your project first to determine how they
1729prefer such patches be handled.
1730
e34caace 1731[[importing-patches]]
d19fbc3c 1732Importing patches to a project
b684f830 1733------------------------------
d19fbc3c
BF
1734
1735Git also provides a tool called gitlink:git-am[1] (am stands for
1736"apply mailbox"), for importing such an emailed series of patches.
1737Just save all of the patch-containing messages, in order, into a
1738single mailbox file, say "patches.mbox", then run
1739
1740-------------------------------------------------
eb6ae7f4 1741$ git am -3 patches.mbox
d19fbc3c
BF
1742-------------------------------------------------
1743
1744Git will apply each patch in order; if any conflicts are found, it
1745will stop, and you can fix the conflicts as described in
01997b4a
BF
1746"<<resolving-a-merge,Resolving a merge>>". (The "-3" option tells
1747git to perform a merge; if you would prefer it just to abort and
1748leave your tree and index untouched, you may omit that option.)
1749
1750Once the index is updated with the results of the conflict
1751resolution, instead of creating a new commit, just run
d19fbc3c
BF
1752
1753-------------------------------------------------
1754$ git am --resolved
1755-------------------------------------------------
1756
1757and git will create the commit for you and continue applying the
1758remaining patches from the mailbox.
1759
1760The final result will be a series of commits, one for each patch in
1761the original mailbox, with authorship and commit log message each
1762taken from the message containing each patch.
1763
eda69449
BF
1764[[public-repositories]]
1765Public git repositories
1766-----------------------
d19fbc3c 1767
6e30fb0c
DK
1768Another way to submit changes to a project is to tell the maintainer
1769of that project to pull the changes from your repository using
1770gitlink:git-pull[1]. In the section "<<getting-updates-with-git-pull,
1771Getting updates with git pull>>" we described this as a way to get
1772updates from the "main" repository, but it works just as well in the
1773other direction.
d19fbc3c 1774
eda69449
BF
1775If you and the maintainer both have accounts on the same machine, then
1776you can just pull changes from each other's repositories directly;
11d51533 1777commands that accept repository URLs as arguments will also accept a
eda69449 1778local directory name:
d19fbc3c
BF
1779
1780-------------------------------------------------
1781$ git clone /path/to/repository
1782$ git pull /path/to/other/repository
1783-------------------------------------------------
1784
11d51533
BF
1785or an ssh url:
1786
1787-------------------------------------------------
1788$ git clone ssh://yourhost/~you/repository
1789-------------------------------------------------
1790
1791For projects with few developers, or for synchronizing a few private
1792repositories, this may be all you need.
1793
eda69449
BF
1794However, the more common way to do this is to maintain a separate public
1795repository (usually on a different host) for others to pull changes
1796from. This is usually more convenient, and allows you to cleanly
1797separate private work in progress from publicly visible work.
d19fbc3c
BF
1798
1799You will continue to do your day-to-day work in your personal
1800repository, but periodically "push" changes from your personal
1801repository into your public repository, allowing other developers to
1802pull from that repository. So the flow of changes, in a situation
1803where there is one other developer with a public repository, looks
1804like this:
1805
1806 you push
1807 your personal repo ------------------> your public repo
a6080a0a 1808 ^ |
d19fbc3c
BF
1809 | |
1810 | you pull | they pull
1811 | |
1812 | |
1813 | they push V
1814 their public repo <------------------- their repo
1815
11d51533
BF
1816We explain how to do this in the following sections.
1817
eda69449
BF
1818[[setting-up-a-public-repository]]
1819Setting up a public repository
1820~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1821
1822Assume your personal repository is in the directory ~/proj. We
1823first create a new clone of the repository and tell git-daemon that it
1824is meant to be public:
d19fbc3c
BF
1825
1826-------------------------------------------------
52c80037 1827$ git clone --bare ~/proj proj.git
eda69449 1828$ touch proj.git/git-daemon-export-ok
d19fbc3c
BF
1829-------------------------------------------------
1830
52c80037 1831The resulting directory proj.git contains a "bare" git repository--it is
eda69449
BF
1832just the contents of the ".git" directory, without any files checked out
1833around it.
d19fbc3c 1834
c64415e2 1835Next, copy proj.git to the server where you plan to host the
d19fbc3c
BF
1836public repository. You can use scp, rsync, or whatever is most
1837convenient.
1838
eda69449
BF
1839[[exporting-via-git]]
1840Exporting a git repository via the git protocol
1841~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1842
1843This is the preferred method.
1844
1845If someone else administers the server, they should tell you what
1846directory to put the repository in, and what git:// url it will appear
1847at. You can then skip to the section
d19fbc3c
BF
1848"<<pushing-changes-to-a-public-repository,Pushing changes to a public
1849repository>>", below.
1850
eda69449
BF
1851Otherwise, all you need to do is start gitlink:git-daemon[1]; it will
1852listen on port 9418. By default, it will allow access to any directory
1853that looks like a git directory and contains the magic file
1854git-daemon-export-ok. Passing some directory paths as git-daemon
1855arguments will further restrict the exports to those paths.
1856
1857You can also run git-daemon as an inetd service; see the
1858gitlink:git-daemon[1] man page for details. (See especially the
1859examples section.)
d19fbc3c
BF
1860
1861[[exporting-via-http]]
1862Exporting a git repository via http
eda69449 1863~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
BF
1864
1865The git protocol gives better performance and reliability, but on a
1866host with a web server set up, http exports may be simpler to set up.
1867
1868All you need to do is place the newly created bare git repository in
1869a directory that is exported by the web server, and make some
1870adjustments to give web clients some extra information they need:
1871
1872-------------------------------------------------
1873$ mv proj.git /home/you/public_html/proj.git
1874$ cd proj.git
c64415e2 1875$ git --bare update-server-info
d19fbc3c
BF
1876$ chmod a+x hooks/post-update
1877-------------------------------------------------
1878
1879(For an explanation of the last two lines, see
1880gitlink:git-update-server-info[1], and the documentation
a2983cb7 1881link:hooks.html[Hooks used by git].)
d19fbc3c
BF
1882
1883Advertise the url of proj.git. Anybody else should then be able to
02783075 1884clone or pull from that url, for example with a command line like:
d19fbc3c
BF
1885
1886-------------------------------------------------
1887$ git clone http://yourserver.com/~you/proj.git
1888-------------------------------------------------
1889
1890(See also
1891link:howto/setup-git-server-over-http.txt[setup-git-server-over-http]
1892for a slightly more sophisticated setup using WebDAV which also
1893allows pushing over http.)
1894
d19fbc3c
BF
1895[[pushing-changes-to-a-public-repository]]
1896Pushing changes to a public repository
eda69449 1897~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c 1898
eda69449 1899Note that the two techniques outlined above (exporting via
d19fbc3c
BF
1900<<exporting-via-http,http>> or <<exporting-via-git,git>>) allow other
1901maintainers to fetch your latest changes, but they do not allow write
1902access, which you will need to update the public repository with the
1903latest changes created in your private repository.
1904
1905The simplest way to do this is using gitlink:git-push[1] and ssh; to
1906update the remote branch named "master" with the latest state of your
1907branch named "master", run
1908
1909-------------------------------------------------
1910$ git push ssh://yourserver.com/~you/proj.git master:master
1911-------------------------------------------------
1912
1913or just
1914
1915-------------------------------------------------
1916$ git push ssh://yourserver.com/~you/proj.git master
1917-------------------------------------------------
1918
1919As with git-fetch, git-push will complain if this does not result in
1920a <<fast-forwards,fast forward>>. Normally this is a sign of
1921something wrong. However, if you are sure you know what you're
1922doing, you may force git-push to perform the update anyway by
1923proceeding the branch name by a plus sign:
1924
1925-------------------------------------------------
1926$ git push ssh://yourserver.com/~you/proj.git +master
1927-------------------------------------------------
1928
11d51533
BF
1929Note that the target of a "push" is normally a
1930<<def_bare_repository,bare>> repository. You can also push to a
1931repository that has a checked-out working tree, but the working tree
1932will not be updated by the push. This may lead to unexpected results if
1933the branch you push to is the currently checked-out branch!
1934
d19fbc3c
BF
1935As with git-fetch, you may also set up configuration options to
1936save typing; so, for example, after
1937
1938-------------------------------------------------
c64415e2 1939$ cat >>.git/config <<EOF
d19fbc3c
BF
1940[remote "public-repo"]
1941 url = ssh://yourserver.com/~you/proj.git
1942EOF
1943-------------------------------------------------
1944
1945you should be able to perform the above push with just
1946
1947-------------------------------------------------
1948$ git push public-repo master
1949-------------------------------------------------
1950
1951See the explanations of the remote.<name>.url, branch.<name>.remote,
9d13bda3 1952and remote.<name>.push options in gitlink:git-config[1] for
d19fbc3c
BF
1953details.
1954
e34caace 1955[[setting-up-a-shared-repository]]
d19fbc3c 1956Setting up a shared repository
eda69449 1957~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
BF
1958
1959Another way to collaborate is by using a model similar to that
1960commonly used in CVS, where several developers with special rights
1961all push to and pull from a single shared repository. See
a2983cb7 1962link:cvs-migration.html[git for CVS users] for instructions on how to
d19fbc3c
BF
1963set this up.
1964
8fae2225
BF
1965However, while there is nothing wrong with git's support for shared
1966repositories, this mode of operation is not generally recommended,
1967simply because the mode of collaboration that git supports--by
1968exchanging patches and pulling from public repositories--has so many
1969advantages over the central shared repository:
1970
1971 - Git's ability to quickly import and merge patches allows a
1972 single maintainer to process incoming changes even at very
1973 high rates. And when that becomes too much, git-pull provides
1974 an easy way for that maintainer to delegate this job to other
1975 maintainers while still allowing optional review of incoming
1976 changes.
1977 - Since every developer's repository has the same complete copy
1978 of the project history, no repository is special, and it is
1979 trivial for another developer to take over maintenance of a
1980 project, either by mutual agreement, or because a maintainer
1981 becomes unresponsive or difficult to work with.
1982 - The lack of a central group of "committers" means there is
1983 less need for formal decisions about who is "in" and who is
1984 "out".
1985
e34caace 1986[[setting-up-gitweb]]
eda69449
BF
1987Allowing web browsing of a repository
1988~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c 1989
a8cd1402
BF
1990The gitweb cgi script provides users an easy way to browse your
1991project's files and history without having to install git; see the file
04483524 1992gitweb/INSTALL in the git source tree for instructions on setting it up.
d19fbc3c 1993
e34caace 1994[[sharing-development-examples]]
b684f830
BF
1995Examples
1996--------
d19fbc3c 1997
9e2163ea
BF
1998[[maintaining-topic-branches]]
1999Maintaining topic branches for a Linux subsystem maintainer
2000~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2001
2002This describes how Tony Luck uses git in his role as maintainer of the
2003IA64 architecture for the Linux kernel.
2004
2005He uses two public branches:
2006
2007 - A "test" tree into which patches are initially placed so that they
2008 can get some exposure when integrated with other ongoing development.
2009 This tree is available to Andrew for pulling into -mm whenever he
2010 wants.
2011
2012 - A "release" tree into which tested patches are moved for final sanity
2013 checking, and as a vehicle to send them upstream to Linus (by sending
2014 him a "please pull" request.)
2015
2016He also uses a set of temporary branches ("topic branches"), each
2017containing a logical grouping of patches.
2018
2019To set this up, first create your work tree by cloning Linus's public
2020tree:
2021
2022-------------------------------------------------
2023$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git work
2024$ cd work
2025-------------------------------------------------
2026
2027Linus's tree will be stored in the remote branch named origin/master,
2028and can be updated using gitlink:git-fetch[1]; you can track other
2029public trees using gitlink:git-remote[1] to set up a "remote" and
6e30fb0c
DK
2030gitlink:git-fetch[1] to keep them up-to-date; see
2031<<repositories-and-branches>>.
9e2163ea
BF
2032
2033Now create the branches in which you are going to work; these start out
2034at the current tip of origin/master branch, and should be set up (using
2035the --track option to gitlink:git-branch[1]) to merge changes in from
2036Linus by default.
2037
2038-------------------------------------------------
2039$ git branch --track test origin/master
2040$ git branch --track release origin/master
2041-------------------------------------------------
2042
2043These can be easily kept up to date using gitlink:git-pull[1]
2044
2045-------------------------------------------------
2046$ git checkout test && git pull
2047$ git checkout release && git pull
2048-------------------------------------------------
2049
2050Important note! If you have any local changes in these branches, then
2051this merge will create a commit object in the history (with no local
2052changes git will simply do a "Fast forward" merge). Many people dislike
2053the "noise" that this creates in the Linux history, so you should avoid
2054doing this capriciously in the "release" branch, as these noisy commits
2055will become part of the permanent history when you ask Linus to pull
2056from the release branch.
2057
2058A few configuration variables (see gitlink:git-config[1]) can
2059make it easy to push both branches to your public tree. (See
2060<<setting-up-a-public-repository>>.)
2061
2062-------------------------------------------------
2063$ cat >> .git/config <<EOF
2064[remote "mytree"]
2065 url = master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git
2066 push = release
2067 push = test
2068EOF
2069-------------------------------------------------
2070
2071Then you can push both the test and release trees using
2072gitlink:git-push[1]:
2073
2074-------------------------------------------------
2075$ git push mytree
2076-------------------------------------------------
2077
2078or push just one of the test and release branches using:
2079
2080-------------------------------------------------
2081$ git push mytree test
2082-------------------------------------------------
2083
2084or
2085
2086-------------------------------------------------
2087$ git push mytree release
2088-------------------------------------------------
2089
2090Now to apply some patches from the community. Think of a short
2091snappy name for a branch to hold this patch (or related group of
2092patches), and create a new branch from the current tip of Linus's
2093branch:
2094
2095-------------------------------------------------
2096$ git checkout -b speed-up-spinlocks origin
2097-------------------------------------------------
2098
2099Now you apply the patch(es), run some tests, and commit the change(s). If
2100the patch is a multi-part series, then you should apply each as a separate
2101commit to this branch.
2102
2103-------------------------------------------------
2104$ ... patch ... test ... commit [ ... patch ... test ... commit ]*
2105-------------------------------------------------
2106
2107When you are happy with the state of this change, you can pull it into the
2108"test" branch in preparation to make it public:
2109
2110-------------------------------------------------
2111$ git checkout test && git pull . speed-up-spinlocks
2112-------------------------------------------------
2113
2114It is unlikely that you would have any conflicts here ... but you might if you
2115spent a while on this step and had also pulled new versions from upstream.
2116
2117Some time later when enough time has passed and testing done, you can pull the
2118same branch into the "release" tree ready to go upstream. This is where you
2119see the value of keeping each patch (or patch series) in its own branch. It
2120means that the patches can be moved into the "release" tree in any order.
2121
2122-------------------------------------------------
2123$ git checkout release && git pull . speed-up-spinlocks
2124-------------------------------------------------
2125
2126After a while, you will have a number of branches, and despite the
2127well chosen names you picked for each of them, you may forget what
2128they are for, or what status they are in. To get a reminder of what
2129changes are in a specific branch, use:
2130
2131-------------------------------------------------
2132$ git log linux..branchname | git-shortlog
2133-------------------------------------------------
2134
2135To see whether it has already been merged into the test or release branches
2136use:
2137
2138-------------------------------------------------
2139$ git log test..branchname
2140-------------------------------------------------
2141
2142or
2143
2144-------------------------------------------------
2145$ git log release..branchname
2146-------------------------------------------------
2147
2148(If this branch has not yet been merged you will see some log entries.
2149If it has been merged, then there will be no output.)
2150
2151Once a patch completes the great cycle (moving from test to release,
2152then pulled by Linus, and finally coming back into your local
2153"origin/master" branch) the branch for this change is no longer needed.
2154You detect this when the output from:
2155
2156-------------------------------------------------
2157$ git log origin..branchname
2158-------------------------------------------------
2159
2160is empty. At this point the branch can be deleted:
2161
2162-------------------------------------------------
2163$ git branch -d branchname
2164-------------------------------------------------
2165
2166Some changes are so trivial that it is not necessary to create a separate
2167branch and then merge into each of the test and release branches. For
2168these changes, just apply directly to the "release" branch, and then
2169merge that into the "test" branch.
2170
2171To create diffstat and shortlog summaries of changes to include in a "please
2172pull" request to Linus you can use:
2173
2174-------------------------------------------------
2175$ git diff --stat origin..release
2176-------------------------------------------------
2177
2178and
2179
2180-------------------------------------------------
2181$ git log -p origin..release | git shortlog
2182-------------------------------------------------
2183
2184Here are some of the scripts that simplify all this even further.
2185
2186-------------------------------------------------
2187==== update script ====
2188# Update a branch in my GIT tree. If the branch to be updated
2189# is origin, then pull from kernel.org. Otherwise merge
2190# origin/master branch into test|release branch
2191
2192case "$1" in
2193test|release)
2194 git checkout $1 && git pull . origin
2195 ;;
2196origin)
fc74ecc1 2197 before=$(git rev-parse refs/remotes/origin/master)
9e2163ea 2198 git fetch origin
fc74ecc1 2199 after=$(git rev-parse refs/remotes/origin/master)
9e2163ea
BF
2200 if [ $before != $after ]
2201 then
2202 git log $before..$after | git shortlog
2203 fi
2204 ;;
2205*)
2206 echo "Usage: $0 origin|test|release" 1>&2
2207 exit 1
2208 ;;
2209esac
2210-------------------------------------------------
2211
2212-------------------------------------------------
2213==== merge script ====
2214# Merge a branch into either the test or release branch
2215
2216pname=$0
2217
2218usage()
2219{
2220 echo "Usage: $pname branch test|release" 1>&2
2221 exit 1
2222}
2223
fc74ecc1 2224git show-ref -q --verify -- refs/heads/"$1" || {
9e2163ea
BF
2225 echo "Can't see branch <$1>" 1>&2
2226 usage
fc74ecc1 2227}
9e2163ea
BF
2228
2229case "$2" in
2230test|release)
2231 if [ $(git log $2..$1 | wc -c) -eq 0 ]
2232 then
2233 echo $1 already merged into $2 1>&2
2234 exit 1
2235 fi
2236 git checkout $2 && git pull . $1
2237 ;;
2238*)
2239 usage
2240 ;;
2241esac
2242-------------------------------------------------
2243
2244-------------------------------------------------
2245==== status script ====
2246# report on status of my ia64 GIT tree
2247
2248gb=$(tput setab 2)
2249rb=$(tput setab 1)
2250restore=$(tput setab 9)
2251
2252if [ `git rev-list test..release | wc -c` -gt 0 ]
2253then
2254 echo $rb Warning: commits in release that are not in test $restore
2255 git log test..release
2256fi
2257
fc74ecc1 2258for branch in `git show-ref --heads | sed 's|^.*/||'`
9e2163ea
BF
2259do
2260 if [ $branch = test -o $branch = release ]
2261 then
2262 continue
2263 fi
2264
2265 echo -n $gb ======= $branch ====== $restore " "
2266 status=
2267 for ref in test release origin/master
2268 do
2269 if [ `git rev-list $ref..$branch | wc -c` -gt 0 ]
2270 then
2271 status=$status${ref:0:1}
2272 fi
2273 done
2274 case $status in
2275 trl)
2276 echo $rb Need to pull into test $restore
2277 ;;
2278 rl)
2279 echo "In test"
2280 ;;
2281 l)
2282 echo "Waiting for linus"
2283 ;;
2284 "")
2285 echo $rb All done $restore
2286 ;;
2287 *)
2288 echo $rb "<$status>" $restore
2289 ;;
2290 esac
2291 git log origin/master..$branch | git shortlog
2292done
2293-------------------------------------------------
d19fbc3c 2294
d19fbc3c 2295
d19fbc3c 2296[[cleaning-up-history]]
4c63ff45
BF
2297Rewriting history and maintaining patch series
2298==============================================
2299
2300Normally commits are only added to a project, never taken away or
2301replaced. Git is designed with this assumption, and violating it will
2302cause git's merge machinery (for example) to do the wrong thing.
2303
2304However, there is a situation in which it can be useful to violate this
2305assumption.
2306
e34caace 2307[[patch-series]]
4c63ff45
BF
2308Creating the perfect patch series
2309---------------------------------
2310
2311Suppose you are a contributor to a large project, and you want to add a
2312complicated feature, and to present it to the other developers in a way
2313that makes it easy for them to read your changes, verify that they are
2314correct, and understand why you made each change.
2315
b181d57f 2316If you present all of your changes as a single patch (or commit), they
79c96c57 2317may find that it is too much to digest all at once.
4c63ff45
BF
2318
2319If you present them with the entire history of your work, complete with
2320mistakes, corrections, and dead ends, they may be overwhelmed.
2321
2322So the ideal is usually to produce a series of patches such that:
2323
2324 1. Each patch can be applied in order.
2325
2326 2. Each patch includes a single logical change, together with a
2327 message explaining the change.
2328
2329 3. No patch introduces a regression: after applying any initial
2330 part of the series, the resulting project still compiles and
2331 works, and has no bugs that it didn't have before.
2332
2333 4. The complete series produces the same end result as your own
2334 (probably much messier!) development process did.
2335
b181d57f
BF
2336We will introduce some tools that can help you do this, explain how to
2337use them, and then explain some of the problems that can arise because
2338you are rewriting history.
4c63ff45 2339
e34caace 2340[[using-git-rebase]]
4c63ff45
BF
2341Keeping a patch series up to date using git-rebase
2342--------------------------------------------------
2343
79c96c57
MC
2344Suppose that you create a branch "mywork" on a remote-tracking branch
2345"origin", and create some commits on top of it:
4c63ff45
BF
2346
2347-------------------------------------------------
2348$ git checkout -b mywork origin
2349$ vi file.txt
2350$ git commit
2351$ vi otherfile.txt
2352$ git commit
2353...
2354-------------------------------------------------
2355
2356You have performed no merges into mywork, so it is just a simple linear
2357sequence of patches on top of "origin":
2358
1dc71a91 2359................................................
4c63ff45
BF
2360 o--o--o <-- origin
2361 \
2362 o--o--o <-- mywork
1dc71a91 2363................................................
4c63ff45
BF
2364
2365Some more interesting work has been done in the upstream project, and
2366"origin" has advanced:
2367
1dc71a91 2368................................................
4c63ff45
BF
2369 o--o--O--o--o--o <-- origin
2370 \
2371 a--b--c <-- mywork
1dc71a91 2372................................................
4c63ff45
BF
2373
2374At this point, you could use "pull" to merge your changes back in;
2375the result would create a new merge commit, like this:
2376
1dc71a91 2377................................................
4c63ff45
BF
2378 o--o--O--o--o--o <-- origin
2379 \ \
2380 a--b--c--m <-- mywork
1dc71a91 2381................................................
a6080a0a 2382
4c63ff45
BF
2383However, if you prefer to keep the history in mywork a simple series of
2384commits without any merges, you may instead choose to use
2385gitlink:git-rebase[1]:
2386
2387-------------------------------------------------
2388$ git checkout mywork
2389$ git rebase origin
2390-------------------------------------------------
2391
b181d57f
BF
2392This will remove each of your commits from mywork, temporarily saving
2393them as patches (in a directory named ".dotest"), update mywork to
2394point at the latest version of origin, then apply each of the saved
2395patches to the new mywork. The result will look like:
4c63ff45
BF
2396
2397
1dc71a91 2398................................................
4c63ff45
BF
2399 o--o--O--o--o--o <-- origin
2400 \
2401 a'--b'--c' <-- mywork
1dc71a91 2402................................................
4c63ff45 2403
b181d57f
BF
2404In the process, it may discover conflicts. In that case it will stop
2405and allow you to fix the conflicts; after fixing conflicts, use "git
2406add" to update the index with those contents, and then, instead of
2407running git-commit, just run
4c63ff45
BF
2408
2409-------------------------------------------------
2410$ git rebase --continue
2411-------------------------------------------------
2412
2413and git will continue applying the rest of the patches.
2414
2415At any point you may use the --abort option to abort this process and
2416return mywork to the state it had before you started the rebase:
2417
2418-------------------------------------------------
2419$ git rebase --abort
2420-------------------------------------------------
2421
e34caace 2422[[modifying-one-commit]]
365aa199
BF
2423Modifying a single commit
2424-------------------------
2425
2426We saw in <<fixing-a-mistake-by-editing-history>> that you can replace the
2427most recent commit using
2428
2429-------------------------------------------------
2430$ git commit --amend
2431-------------------------------------------------
2432
2433which will replace the old commit by a new commit incorporating your
2434changes, giving you a chance to edit the old commit message first.
2435
2436You can also use a combination of this and gitlink:git-rebase[1] to edit
2437commits further back in your history. First, tag the problematic commit with
2438
2439-------------------------------------------------
2440$ git tag bad mywork~5
2441-------------------------------------------------
2442
2443(Either gitk or git-log may be useful for finding the commit.)
2444
25d9f3fa
BF
2445Then check out that commit, edit it, and rebase the rest of the series
2446on top of it (note that we could check out the commit on a temporary
2447branch, but instead we're using a <<detached-head,detached head>>):
365aa199
BF
2448
2449-------------------------------------------------
25d9f3fa 2450$ git checkout bad
365aa199
BF
2451$ # make changes here and update the index
2452$ git commit --amend
25d9f3fa 2453$ git rebase --onto HEAD bad mywork
365aa199
BF
2454-------------------------------------------------
2455
25d9f3fa
BF
2456When you're done, you'll be left with mywork checked out, with the top
2457patches on mywork reapplied on top of your modified commit. You can
365aa199
BF
2458then clean up with
2459
2460-------------------------------------------------
365aa199
BF
2461$ git tag -d bad
2462-------------------------------------------------
2463
2464Note that the immutable nature of git history means that you haven't really
2465"modified" existing commits; instead, you have replaced the old commits with
2466new commits having new object names.
2467
e34caace 2468[[reordering-patch-series]]
4c63ff45
BF
2469Reordering or selecting from a patch series
2470-------------------------------------------
2471
b181d57f
BF
2472Given one existing commit, the gitlink:git-cherry-pick[1] command
2473allows you to apply the change introduced by that commit and create a
2474new commit that records it. So, for example, if "mywork" points to a
2475series of patches on top of "origin", you might do something like:
2476
2477-------------------------------------------------
2478$ git checkout -b mywork-new origin
2479$ gitk origin..mywork &
2480-------------------------------------------------
2481
2482And browse through the list of patches in the mywork branch using gitk,
2483applying them (possibly in a different order) to mywork-new using
407c0c87 2484cherry-pick, and possibly modifying them as you go using commit --amend.
6e30fb0c
DK
2485The gitlink:git-gui[1] command may also help as it allows you to
2486individually select diff hunks for inclusion in the index (by
2487right-clicking on the diff hunk and choosing "Stage Hunk for Commit").
b181d57f
BF
2488
2489Another technique is to use git-format-patch to create a series of
2490patches, then reset the state to before the patches:
4c63ff45 2491
b181d57f
BF
2492-------------------------------------------------
2493$ git format-patch origin
2494$ git reset --hard origin
2495-------------------------------------------------
4c63ff45 2496
b181d57f
BF
2497Then modify, reorder, or eliminate patches as preferred before applying
2498them again with gitlink:git-am[1].
4c63ff45 2499
e34caace 2500[[patch-series-tools]]
4c63ff45
BF
2501Other tools
2502-----------
2503
02783075 2504There are numerous other tools, such as StGIT, which exist for the
79c96c57 2505purpose of maintaining a patch series. These are outside of the scope of
b181d57f 2506this manual.
4c63ff45 2507
e34caace 2508[[problems-with-rewriting-history]]
4c63ff45
BF
2509Problems with rewriting history
2510-------------------------------
2511
b181d57f
BF
2512The primary problem with rewriting the history of a branch has to do
2513with merging. Suppose somebody fetches your branch and merges it into
2514their branch, with a result something like this:
2515
1dc71a91 2516................................................
b181d57f
BF
2517 o--o--O--o--o--o <-- origin
2518 \ \
2519 t--t--t--m <-- their branch:
1dc71a91 2520................................................
b181d57f
BF
2521
2522Then suppose you modify the last three commits:
2523
1dc71a91 2524................................................
b181d57f
BF
2525 o--o--o <-- new head of origin
2526 /
2527 o--o--O--o--o--o <-- old head of origin
1dc71a91 2528................................................
b181d57f
BF
2529
2530If we examined all this history together in one repository, it will
2531look like:
2532
1dc71a91 2533................................................
b181d57f
BF
2534 o--o--o <-- new head of origin
2535 /
2536 o--o--O--o--o--o <-- old head of origin
2537 \ \
2538 t--t--t--m <-- their branch:
1dc71a91 2539................................................
b181d57f
BF
2540
2541Git has no way of knowing that the new head is an updated version of
2542the old head; it treats this situation exactly the same as it would if
2543two developers had independently done the work on the old and new heads
2544in parallel. At this point, if someone attempts to merge the new head
2545in to their branch, git will attempt to merge together the two (old and
2546new) lines of development, instead of trying to replace the old by the
2547new. The results are likely to be unexpected.
2548
2549You may still choose to publish branches whose history is rewritten,
2550and it may be useful for others to be able to fetch those branches in
2551order to examine or test them, but they should not attempt to pull such
2552branches into their own work.
2553
2554For true distributed development that supports proper merging,
2555published branches should never be rewritten.
2556
e34caace 2557[[advanced-branch-management]]
b181d57f
BF
2558Advanced branch management
2559==========================
4c63ff45 2560
e34caace 2561[[fetching-individual-branches]]
b181d57f
BF
2562Fetching individual branches
2563----------------------------
2564
2565Instead of using gitlink:git-remote[1], you can also choose just
2566to update one branch at a time, and to store it locally under an
2567arbitrary name:
2568
2569-------------------------------------------------
2570$ git fetch origin todo:my-todo-work
2571-------------------------------------------------
2572
2573The first argument, "origin", just tells git to fetch from the
2574repository you originally cloned from. The second argument tells git
2575to fetch the branch named "todo" from the remote repository, and to
2576store it locally under the name refs/heads/my-todo-work.
2577
2578You can also fetch branches from other repositories; so
2579
2580-------------------------------------------------
2581$ git fetch git://example.com/proj.git master:example-master
2582-------------------------------------------------
2583
2584will create a new branch named "example-master" and store in it the
2585branch named "master" from the repository at the given URL. If you
2586already have a branch named example-master, it will attempt to
59723040
BF
2587<<fast-forwards,fast-forward>> to the commit given by example.com's
2588master branch. In more detail:
b181d57f 2589
59723040
BF
2590[[fetch-fast-forwards]]
2591git fetch and fast-forwards
2592---------------------------
b181d57f
BF
2593
2594In the previous example, when updating an existing branch, "git
2595fetch" checks to make sure that the most recent commit on the remote
2596branch is a descendant of the most recent commit on your copy of the
2597branch before updating your copy of the branch to point at the new
59723040 2598commit. Git calls this process a <<fast-forwards,fast forward>>.
b181d57f
BF
2599
2600A fast forward looks something like this:
2601
1dc71a91 2602................................................
b181d57f
BF
2603 o--o--o--o <-- old head of the branch
2604 \
2605 o--o--o <-- new head of the branch
1dc71a91 2606................................................
b181d57f
BF
2607
2608
2609In some cases it is possible that the new head will *not* actually be
2610a descendant of the old head. For example, the developer may have
2611realized she made a serious mistake, and decided to backtrack,
2612resulting in a situation like:
2613
1dc71a91 2614................................................
b181d57f
BF
2615 o--o--o--o--a--b <-- old head of the branch
2616 \
2617 o--o--o <-- new head of the branch
1dc71a91 2618................................................
b181d57f
BF
2619
2620In this case, "git fetch" will fail, and print out a warning.
2621
2622In that case, you can still force git to update to the new head, as
2623described in the following section. However, note that in the
2624situation above this may mean losing the commits labeled "a" and "b",
2625unless you've already created a reference of your own pointing to
2626them.
2627
e34caace 2628[[forcing-fetch]]
b181d57f
BF
2629Forcing git fetch to do non-fast-forward updates
2630------------------------------------------------
2631
2632If git fetch fails because the new head of a branch is not a
2633descendant of the old head, you may force the update with:
2634
2635-------------------------------------------------
2636$ git fetch git://example.com/proj.git +master:refs/remotes/example/master
2637-------------------------------------------------
2638
c64415e2
BF
2639Note the addition of the "+" sign. Alternatively, you can use the "-f"
2640flag to force updates of all the fetched branches, as in:
2641
2642-------------------------------------------------
2643$ git fetch -f origin
2644-------------------------------------------------
2645
2646Be aware that commits that the old version of example/master pointed at
2647may be lost, as we saw in the previous section.
b181d57f 2648
e34caace 2649[[remote-branch-configuration]]
b181d57f
BF
2650Configuring remote branches
2651---------------------------
2652
2653We saw above that "origin" is just a shortcut to refer to the
79c96c57 2654repository that you originally cloned from. This information is
b181d57f 2655stored in git configuration variables, which you can see using
9d13bda3 2656gitlink:git-config[1]:
b181d57f
BF
2657
2658-------------------------------------------------
9d13bda3 2659$ git config -l
b181d57f
BF
2660core.repositoryformatversion=0
2661core.filemode=true
2662core.logallrefupdates=true
2663remote.origin.url=git://git.kernel.org/pub/scm/git/git.git
2664remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*
2665branch.master.remote=origin
2666branch.master.merge=refs/heads/master
2667-------------------------------------------------
2668
2669If there are other repositories that you also use frequently, you can
2670create similar configuration options to save typing; for example,
2671after
2672
2673-------------------------------------------------
9d13bda3 2674$ git config remote.example.url git://example.com/proj.git
b181d57f
BF
2675-------------------------------------------------
2676
2677then the following two commands will do the same thing:
2678
2679-------------------------------------------------
2680$ git fetch git://example.com/proj.git master:refs/remotes/example/master
2681$ git fetch example master:refs/remotes/example/master
2682-------------------------------------------------
2683
2684Even better, if you add one more option:
2685
2686-------------------------------------------------
9d13bda3 2687$ git config remote.example.fetch master:refs/remotes/example/master
b181d57f
BF
2688-------------------------------------------------
2689
2690then the following commands will all do the same thing:
2691
2692-------------------------------------------------
52c80037
BF
2693$ git fetch git://example.com/proj.git master:refs/remotes/example/master
2694$ git fetch example master:refs/remotes/example/master
b181d57f
BF
2695$ git fetch example
2696-------------------------------------------------
2697
2698You can also add a "+" to force the update each time:
2699
2700-------------------------------------------------
9d13bda3 2701$ git config remote.example.fetch +master:ref/remotes/example/master
b181d57f
BF
2702-------------------------------------------------
2703
2704Don't do this unless you're sure you won't mind "git fetch" possibly
2705throwing away commits on mybranch.
2706
2707Also note that all of the above configuration can be performed by
2708directly editing the file .git/config instead of using
9d13bda3 2709gitlink:git-config[1].
b181d57f 2710
9d13bda3 2711See gitlink:git-config[1] for more details on the configuration
b181d57f 2712options mentioned above.
d19fbc3c 2713
d19fbc3c 2714
036f8199
BF
2715[[git-concepts]]
2716Git concepts
2717============
d19fbc3c 2718
036f8199
BF
2719Git is built on a small number of simple but powerful ideas. While it
2720is possible to get things done without understanding them, you will find
2721git much more intuitive if you do.
2722
2723We start with the most important, the <<def_object_database,object
2724database>> and the <<def_index,index>>.
b181d57f 2725
e34caace 2726[[the-object-database]]
b181d57f
BF
2727The Object Database
2728-------------------
2729
1bbf1c79
BF
2730
2731We already saw in <<understanding-commits>> that all commits are stored
2732under a 40-digit "object name". In fact, all the information needed to
2733represent the history of a project is stored in objects with such names.
2734In each case the name is calculated by taking the SHA1 hash of the
2735contents of the object. The SHA1 hash is a cryptographic hash function.
2736What that means to us is that it is impossible to find two different
2737objects with the same name. This has a number of advantages; among
2738others:
2739
2740- Git can quickly determine whether two objects are identical or not,
2741 just by comparing names.
2742- Since object names are computed the same way in ever repository, the
2743 same content stored in two repositories will always be stored under
2744 the same name.
2745- Git can detect errors when it reads an object, by checking that the
2746 object's name is still the SHA1 hash of its contents.
2747
2748(See <<object-details>> for the details of the object formatting and
2749SHA1 calculation.)
2750
2751There are four different types of objects: "blob", "tree", "commit", and
2752"tag".
2753
2754- A <<def_blob_object,"blob" object>> is used to store file data.
2755- A <<def_tree_object,"tree" object>> is an object that ties one or more
2756 "blob" objects into a directory structure. In addition, a tree object
2757 can refer to other tree objects, thus creating a directory hierarchy.
2758- A <<def_commit_object,"commit" object>> ties such directory hierarchies
2759 together into a <<def_DAG,directed acyclic graph>> of revisions - each
2760 commit contains the object name of exactly one tree designating the
2761 directory hierarchy at the time of the commit. In addition, a commit
2762 refers to "parent" commit objects that describe the history of how we
2763 arrived at that directory hierarchy.
2764- A <<def_tag_object,"tag" object>> symbolically identifies and can be
2765 used to sign other objects. It contains the object name and type of
2766 another object, a symbolic name (of course!) and, optionally, a
2767 signature.
b181d57f 2768
b181d57f
BF
2769The object types in some more detail:
2770
513d419c
BF
2771[[commit-object]]
2772Commit Object
2773~~~~~~~~~~~~~
b181d57f 2774
1bbf1c79
BF
2775The "commit" object links a physical state of a tree with a description
2776of how we got there and why. Use the --pretty=raw option to
2777gitlink:git-show[1] or gitlink:git-log[1] to examine your favorite
2778commit:
2779
2780------------------------------------------------
2781$ git show -s --pretty=raw 2be7fcb476
2782commit 2be7fcb4764f2dbcee52635b91fedb1b3dcf7ab4
2783tree fb3a8bdd0ceddd019615af4d57a53f43d8cee2bf
2784parent 257a84d9d02e90447b149af58b271c19405edb6a
2785author Dave Watson <dwatson@mimvista.com> 1187576872 -0400
2786committer Junio C Hamano <gitster@pobox.com> 1187591163 -0700
2787
2788 Fix misspelling of 'suppress' in docs
2789
2790 Signed-off-by: Junio C Hamano <gitster@pobox.com>
2791------------------------------------------------
2792
2793As you can see, a commit is defined by:
2794
2795- a tree: The SHA1 name of a tree object (as defined below), representing
2796 the contents of a directory at a certain point in time.
2797- parent(s): The SHA1 name of some number of commits which represent the
2798 immediately prevoius step(s) in the history of the project. The
2799 example above has one parent; merge commits may have more than
2800 one. A commit with no parents is called a "root" commit, and
2801 represents the initial revision of a project. Each project must have
2802 at least one root. A project can also have multiple roots, though
2803 that isn't common (or necessarily a good idea).
2804- an author: The name of the person responsible for this change, together
2805 with its date.
2806- a committer: The name of the person who actually created the commit,
2807 with the date it was done. This may be different from the author, for
2808 example, if the author was someone who wrote a patch and emailed it
2809 to the person who used it to create the commit.
2810- a comment describing this commit.
2811
2812Note that a commit does not itself contain any information about what
2813actually changed; all changes are calculated by comparing the contents
2814of the tree referred to by this commit with the trees associated with
2815its parents. In particular, git does not attempt to record file renames
2816explicitly, though it can identify cases where the existence of the same
2817file data at changing paths suggests a rename. (See, for example, the
2818-M option to gitlink:git-diff[1]).
2819
2820A commit is usually created by gitlink:git-commit[1], which creates a
2821commit whose parent is normally the current HEAD, and whose tree is
2822taken from the content currently stored in the index.
b181d57f 2823
e34caace 2824[[tree-object]]
b181d57f 2825Tree Object
971aa71f 2826~~~~~~~~~~~
b181d57f 2827
1bbf1c79
BF
2828The ever-versatile gitlink:git-show[1] command can also be used to
2829examine tree objects, but gitlink:git-ls-tree[1] will give you more
2830details:
2831
2832------------------------------------------------
2833$ git ls-tree fb3a8bdd0ce
2834100644 blob 63c918c667fa005ff12ad89437f2fdc80926e21c .gitignore
2835100644 blob 5529b198e8d14decbe4ad99db3f7fb632de0439d .mailmap
2836100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3 COPYING
2837040000 tree 2fb783e477100ce076f6bf57e4a6f026013dc745 Documentation
2838100755 blob 3c0032cec592a765692234f1cba47dfdcc3a9200 GIT-VERSION-GEN
2839100644 blob 289b046a443c0647624607d471289b2c7dcd470b INSTALL
2840100644 blob 4eb463797adc693dc168b926b6932ff53f17d0b1 Makefile
2841100644 blob 548142c327a6790ff8821d67c2ee1eff7a656b52 README
2842...
2843------------------------------------------------
2844
2845As you can see, a tree object contains a list of entries, each with a
2846mode, object type, SHA1 name, and name, sorted by name. It represents
2847the contents of a single directory tree.
2848
2849The object type may be a blob, representing the contents of a file, or
2850another tree, representing the contents of a subdirectory. Since trees
2851and blobs, like all other objects, are named by the SHA1 hash of their
2852contents, two trees have the same SHA1 name if and only if their
2853contents (including, recursively, the contents of all subdirectories)
2854are identical. This allows git to quickly determine the differences
2855between two related tree objects, since it can ignore any entries with
2856identical object names.
2857
2858(Note: in the presence of submodules, trees may also have commits as
6dd14366 2859entries. See <<submodules>> for documentation.)
1bbf1c79
BF
2860
2861Note that the files all have mode 644 or 755: git actually only pays
2862attention to the executable bit.
b181d57f 2863
513d419c
BF
2864[[blob-object]]
2865Blob Object
2866~~~~~~~~~~~
b181d57f 2867
1bbf1c79
BF
2868You can use gitlink:git-show[1] to examine the contents of a blob; take,
2869for example, the blob in the entry for "COPYING" from the tree above:
b181d57f 2870
1bbf1c79
BF
2871------------------------------------------------
2872$ git show 6ff87c4664
2873
2874 Note that the only valid version of the GPL as far as this project
2875 is concerned is _this_ particular version of the license (ie v2, not
2876 v2.2 or v3.x or whatever), unless explicitly otherwise stated.
2877...
2878------------------------------------------------
b181d57f 2879
1bbf1c79
BF
2880A "blob" object is nothing but a binary blob of data. It doesn't refer
2881to anything else or have attributes of any kind.
2882
2883Since the blob is entirely defined by its data, if two files in a
2884directory tree (or in multiple different versions of the repository)
2885have the same contents, they will share the same blob object. The object
2886is totally independent of its location in the directory tree, and
2887renaming a file does not change the object that file is associated with.
2888
2889Note that any tree or blob object can be examined using
2890gitlink:git-show[1] with the <revision>:<path> syntax. This can
2891sometimes be useful for browsing the contents of a tree that is not
2892currently checked out.
b181d57f 2893
e34caace 2894[[trust]]
b181d57f 2895Trust
971aa71f 2896~~~~~
b181d57f 2897
1bbf1c79
BF
2898If you receive the SHA1 name of a blob from one source, and its contents
2899from another (possibly untrusted) source, you can still trust that those
2900contents are correct as long as the SHA1 name agrees. This is because
2901the SHA1 is designed so that it is infeasible to find different contents
2902that produce the same hash.
b181d57f 2903
1bbf1c79
BF
2904Similarly, you need only trust the SHA1 name of a top-level tree object
2905to trust the contents of the entire directory that it refers to, and if
2906you receive the SHA1 name of a commit from a trusted source, then you
2907can easily verify the entire history of commits reachable through
2908parents of that commit, and all of those contents of the trees referred
2909to by those commits.
b181d57f
BF
2910
2911So to introduce some real trust in the system, the only thing you need
2912to do is to digitally sign just 'one' special note, which includes the
2913name of a top-level commit. Your digital signature shows others
2914that you trust that commit, and the immutability of the history of
2915commits tells others that they can trust the whole history.
2916
2917In other words, you can easily validate a whole archive by just
2918sending out a single email that tells the people the name (SHA1 hash)
2919of the top commit, and digitally sign that email using something
2920like GPG/PGP.
2921
2922To assist in this, git also provides the tag object...
2923
e34caace 2924[[tag-object]]
b181d57f 2925Tag Object
971aa71f 2926~~~~~~~~~~
b181d57f 2927
1bbf1c79
BF
2928A tag object contains an object, object type, tag name, the name of the
2929person ("tagger") who created the tag, and a message, which may contain
2930a signature, as can be seen using the gitlink:git-cat-file[1]:
b181d57f 2931
1bbf1c79
BF
2932------------------------------------------------
2933$ git cat-file tag v1.5.0
2934object 437b1b20df4b356c9342dac8d38849f24ef44f27
2935type commit
2936tag v1.5.0
2937tagger Junio C Hamano <junkio@cox.net> 1171411200 +0000
2938
2939GIT 1.5.0
2940-----BEGIN PGP SIGNATURE-----
2941Version: GnuPG v1.4.6 (GNU/Linux)
2942
2943iD8DBQBF0lGqwMbZpPMRm5oRAuRiAJ9ohBLd7s2kqjkKlq1qqC57SbnmzQCdG4ui
2944nLE/L9aUXdWeTFPron96DLA=
2945=2E+0
2946-----END PGP SIGNATURE-----
2947------------------------------------------------
b181d57f 2948
1bbf1c79
BF
2949See the gitlink:git-tag[1] command to learn how to create and verify tag
2950objects. (Note that gitlink:git-tag[1] can also be used to create
2951"lightweight tags", which are not tag objects at all, but just simple
fc74ecc1 2952references whose names begin with "refs/tags/").
b181d57f 2953
09eff7b0
BF
2954[[pack-files]]
2955How git stores objects efficiently: pack files
2956~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2957
9644ffdd
BF
2958Newly created objects are initially created in a file named after the
2959object's SHA1 hash (stored in .git/objects).
09eff7b0
BF
2960
2961Unfortunately this system becomes inefficient once a project has a
2962lot of objects. Try this on an old project:
2963
2964------------------------------------------------
2965$ git count-objects
29666930 objects, 47620 kilobytes
2967------------------------------------------------
2968
2969The first number is the number of objects which are kept in
2970individual files. The second is the amount of space taken up by
2971those "loose" objects.
2972
2973You can save space and make git faster by moving these loose objects in
2974to a "pack file", which stores a group of objects in an efficient
2975compressed format; the details of how pack files are formatted can be
2976found in link:technical/pack-format.txt[technical/pack-format.txt].
2977
2978To put the loose objects into a pack, just run git repack:
2979
2980------------------------------------------------
2981$ git repack
2982Generating pack...
2983Done counting 6020 objects.
2984Deltifying 6020 objects.
2985 100% (6020/6020) done
2986Writing 6020 objects.
2987 100% (6020/6020) done
2988Total 6020, written 6020 (delta 4070), reused 0 (delta 0)
2989Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created.
2990------------------------------------------------
2991
2992You can then run
2993
2994------------------------------------------------
2995$ git prune
2996------------------------------------------------
2997
2998to remove any of the "loose" objects that are now contained in the
2999pack. This will also remove any unreferenced objects (which may be
3000created when, for example, you use "git reset" to remove a commit).
3001You can verify that the loose objects are gone by looking at the
3002.git/objects directory or by running
3003
3004------------------------------------------------
3005$ git count-objects
30060 objects, 0 kilobytes
3007------------------------------------------------
3008
3009Although the object files are gone, any commands that refer to those
3010objects will work exactly as they did before.
3011
3012The gitlink:git-gc[1] command performs packing, pruning, and more for
3013you, so is normally the only high-level command you need.
3014
3015[[dangling-objects]]
3016Dangling objects
3017~~~~~~~~~~~~~~~~
3018
3019The gitlink:git-fsck[1] command will sometimes complain about dangling
3020objects. They are not a problem.
3021
3022The most common cause of dangling objects is that you've rebased a
3023branch, or you have pulled from somebody else who rebased a branch--see
3024<<cleaning-up-history>>. In that case, the old head of the original
3025branch still exists, as does everything it pointed to. The branch
3026pointer itself just doesn't, since you replaced it with another one.
3027
3028There are also other situations that cause dangling objects. For
3029example, a "dangling blob" may arise because you did a "git add" of a
3030file, but then, before you actually committed it and made it part of the
3031bigger picture, you changed something else in that file and committed
3032that *updated* thing - the old state that you added originally ends up
3033not being pointed to by any commit or tree, so it's now a dangling blob
3034object.
3035
3036Similarly, when the "recursive" merge strategy runs, and finds that
3037there are criss-cross merges and thus more than one merge base (which is
3038fairly unusual, but it does happen), it will generate one temporary
3039midway tree (or possibly even more, if you had lots of criss-crossing
3040merges and more than two merge bases) as a temporary internal merge
3041base, and again, those are real objects, but the end result will not end
3042up pointing to them, so they end up "dangling" in your repository.
3043
3044Generally, dangling objects aren't anything to worry about. They can
3045even be very useful: if you screw something up, the dangling objects can
3046be how you recover your old tree (say, you did a rebase, and realized
3047that you really didn't want to - you can look at what dangling objects
3048you have, and decide to reset your head to some old dangling state).
3049
3050For commits, you can just use:
3051
3052------------------------------------------------
3053$ gitk <dangling-commit-sha-goes-here> --not --all
3054------------------------------------------------
3055
3056This asks for all the history reachable from the given commit but not
3057from any branch, tag, or other reference. If you decide it's something
3058you want, you can always create a new reference to it, e.g.,
3059
3060------------------------------------------------
3061$ git branch recovered-branch <dangling-commit-sha-goes-here>
3062------------------------------------------------
3063
3064For blobs and trees, you can't do the same, but you can still examine
3065them. You can just do
3066
3067------------------------------------------------
3068$ git show <dangling-blob/tree-sha-goes-here>
3069------------------------------------------------
3070
3071to show what the contents of the blob were (or, for a tree, basically
3072what the "ls" for that directory was), and that may give you some idea
3073of what the operation was that left that dangling object.
3074
3075Usually, dangling blobs and trees aren't very interesting. They're
3076almost always the result of either being a half-way mergebase (the blob
3077will often even have the conflict markers from a merge in it, if you
3078have had conflicting merges that you fixed up by hand), or simply
3079because you interrupted a "git fetch" with ^C or something like that,
3080leaving _some_ of the new objects in the object database, but just
3081dangling and useless.
3082
3083Anyway, once you are sure that you're not interested in any dangling
3084state, you can just prune all unreachable objects:
3085
3086------------------------------------------------
3087$ git prune
3088------------------------------------------------
3089
3090and they'll be gone. But you should only run "git prune" on a quiescent
3091repository - it's kind of like doing a filesystem fsck recovery: you
3092don't want to do that while the filesystem is mounted.
3093
3094(The same is true of "git-fsck" itself, btw - but since
3095git-fsck never actually *changes* the repository, it just reports
3096on what it found, git-fsck itself is never "dangerous" to run.
3097Running it while somebody is actually changing the repository can cause
3098confusing and scary messages, but it won't actually do anything bad. In
3099contrast, running "git prune" while somebody is actively changing the
3100repository is a *BAD* idea).
b181d57f 3101
e34caace 3102[[the-index]]
1c097891
BF
3103The index
3104-----------
3105
3106The index is a binary file (generally kept in .git/index) containing a
3107sorted list of path names, each with permissions and the SHA1 of a blob
3108object; gitlink:git-ls-files[1] can show you the contents of the index:
b181d57f 3109
1c097891
BF
3110-------------------------------------------------
3111$ git ls-files --stage
3112100644 63c918c667fa005ff12ad89437f2fdc80926e21c 0 .gitignore
3113100644 5529b198e8d14decbe4ad99db3f7fb632de0439d 0 .mailmap
3114100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 0 COPYING
3115100644 a37b2152bd26be2c2289e1f57a292534a51a93c7 0 Documentation/.gitignore
3116100644 fbefe9a45b00a54b58d94d06eca48b03d40a50e0 0 Documentation/Makefile
3117...
3118100644 2511aef8d89ab52be5ec6a5e46236b4b6bcd07ea 0 xdiff/xtypes.h
3119100644 2ade97b2574a9f77e7ae4002a4e07a6a38e46d07 0 xdiff/xutils.c
3120100644 d5de8292e05e7c36c4b68857c1cf9855e3d2f70a 0 xdiff/xutils.h
3121-------------------------------------------------
3122
3123Note that in older documentation you may see the index called the
3124"current directory cache" or just the "cache". It has three important
3125properties:
3126
31271. The index contains all the information necessary to generate a single
3128(uniquely determined) tree object.
3129+
3130For example, running gitlink:git-commit[1] generates this tree object
3131from the index, stores it in the object database, and uses it as the
3132tree object associated with the new commit.
3133
31342. The index enables fast comparisons between the tree object it defines
3135and the working tree.
3136+
3137It does this by storing some additional data for each entry (such as
3138the last modified time). This data is not displayed above, and is not
3139stored in the created tree object, but it can be used to determine
3140quickly which files in the working directory differ from what was
3141stored in the index, and thus save git from having to read all of the
3142data from such files to look for changes.
3143
31443. It can efficiently represent information about merge conflicts
3145between different tree objects, allowing each pathname to be
b181d57f 3146associated with sufficient information about the trees involved that
1c097891
BF
3147you can create a three-way merge between them.
3148+
3149We saw in <<conflict-resolution>> that during a merge the index can
3150store multiple versions of a single file (called "stages"). The third
3151column in the gitlink:git-ls-files[1] output above is the stage
3152number, and will take on values other than 0 for files with merge
3153conflicts.
3154
3155The index is thus a sort of temporary staging area, which is filled with
3156a tree which you are in the process of working on.
3157
3158If you blow the index away entirely, you generally haven't lost any
3159information as long as you have the name of the tree that it described.
b181d57f 3160
38a457ba
MV
3161[[submodules]]
3162Submodules
3163==========
3164
6dd14366
MS
3165Large projects are often composed of smaller, self-contained modules. For
3166example, an embedded Linux distribution's source tree would include every
3167piece of software in the distribution with some local modifications; a movie
3168player might need to build against a specific, known-working version of a
3169decompression library; several independent programs might all share the same
3170build scripts.
3171
3172With centralized revision control systems this is often accomplished by
3173including every module in one single repository. Developers can check out
3174all modules or only the modules they need to work with. They can even modify
3175files across several modules in a single commit while moving things around
3176or updating APIs and translations.
3177
3178Git does not allow partial checkouts, so duplicating this approach in Git
3179would force developers to keep a local copy of modules they are not
3180interested in touching. Commits in an enormous checkout would be slower
3181than you'd expect as Git would have to scan every directory for changes.
3182If modules have a lot of local history, clones would take forever.
3183
3184On the plus side, distributed revision control systems can much better
3185integrate with external sources. In a centralized model, a single arbitrary
3186snapshot of the external project is exported from its own revision control
3187and then imported into the local revision control on a vendor branch. All
3188the history is hidden. With distributed revision control you can clone the
3189entire external history and much more easily follow development and re-merge
3190local changes.
3191
3192Git's submodule support allows a repository to contain, as a subdirectory, a
3193checkout of an external project. Submodules maintain their own identity;
3194the submodule support just stores the submodule repository location and
3195commit ID, so other developers who clone the containing project
3196("superproject") can easily clone all the submodules at the same revision.
3197Partial checkouts of the superproject are possible: you can tell Git to
3198clone none, some or all of the submodules.
3199
3200The gitlink:git-submodule[1] command is available since Git 1.5.3. Users
3201with Git 1.5.2 can look up the submodule commits in the repository and
3202manually check them out; earlier versions won't recognize the submodules at
3203all.
38a457ba
MV
3204
3205To see how submodule support works, create (for example) four example
3206repositories that can be used later as a submodule:
3207
3208-------------------------------------------------
3209$ mkdir ~/git
3210$ cd ~/git
3211$ for i in a b c d
3212do
3213 mkdir $i
3214 cd $i
3215 git init
3216 echo "module $i" > $i.txt
3217 git add $i.txt
3218 git commit -m "Initial commit, submodule $i"
3219 cd ..
3220done
3221-------------------------------------------------
3222
3223Now create the superproject and add all the submodules:
3224
3225-------------------------------------------------
3226$ mkdir super
3227$ cd super
3228$ git init
3229$ for i in a b c d
3230do
3231 git submodule add ~/git/$i
3232done
3233-------------------------------------------------
3234
3235NOTE: Do not use local URLs here if you plan to publish your superproject!
3236
3237See what files `git submodule` created:
3238
3239-------------------------------------------------
3240$ ls -a
3241. .. .git .gitmodules a b c d
3242-------------------------------------------------
3243
3244The `git submodule add` command does a couple of things:
3245
3246- It clones the submodule under the current directory and by default checks out
3247 the master branch.
6dd14366
MS
3248- It adds the submodule's clone path to the gitlink:gitmodules[5] file and
3249 adds this file to the index, ready to be committed.
38a457ba
MV
3250- It adds the submodule's current commit ID to the index, ready to be
3251 committed.
3252
3253Commit the superproject:
3254
3255-------------------------------------------------
3256$ git commit -m "Add submodules a, b, c and d."
3257-------------------------------------------------
3258
3259Now clone the superproject:
3260
3261-------------------------------------------------
3262$ cd ..
3263$ git clone super cloned
3264$ cd cloned
3265-------------------------------------------------
3266
3267The submodule directories are there, but they're empty:
3268
3269-------------------------------------------------
3270$ ls -a a
3271. ..
3272$ git submodule status
3273-d266b9873ad50488163457f025db7cdd9683d88b a
3274-e81d457da15309b4fef4249aba9b50187999670d b
3275-c1536a972b9affea0f16e0680ba87332dc059146 c
3276-d96249ff5d57de5de093e6baff9e0aafa5276a74 d
3277-------------------------------------------------
3278
3279NOTE: The commit object names shown above would be different for you, but they
3280should match the HEAD commit object names of your repositories. You can check
3281it by running `git ls-remote ../a`.
3282
3283Pulling down the submodules is a two-step process. First run `git submodule
3284init` to add the submodule repository URLs to `.git/config`:
3285
3286-------------------------------------------------
3287$ git submodule init
3288-------------------------------------------------
3289
3290Now use `git submodule update` to clone the repositories and check out the
3291commits specified in the superproject:
3292
3293-------------------------------------------------
3294$ git submodule update
3295$ cd a
3296$ ls -a
3297. .. .git a.txt
3298-------------------------------------------------
3299
3300One major difference between `git submodule update` and `git submodule add` is
3301that `git submodule update` checks out a specific commit, rather than the tip
3302of a branch. It's like checking out a tag: the head is detached, so you're not
3303working on a branch.
3304
3305-------------------------------------------------
3306$ git branch
3307* (no branch)
3308 master
3309-------------------------------------------------
3310
3311If you want to make a change within a submodule and you have a detached head,
3312then you should create or checkout a branch, make your changes, publish the
3313change within the submodule, and then update the superproject to reference the
3314new commit:
3315
3316-------------------------------------------------
3317$ git checkout master
3318-------------------------------------------------
3319
3320or
3321
3322-------------------------------------------------
3323$ git checkout -b fix-up
3324-------------------------------------------------
3325
3326then
3327
3328-------------------------------------------------
3329$ echo "adding a line again" >> a.txt
3330$ git commit -a -m "Updated the submodule from within the superproject."
3331$ git push
3332$ cd ..
3333$ git diff
3334diff --git a/a b/a
3335index d266b98..261dfac 160000
3336--- a/a
3337+++ b/a
3338@@ -1 +1 @@
3339-Subproject commit d266b9873ad50488163457f025db7cdd9683d88b
3340+Subproject commit 261dfac35cb99d380eb966e102c1197139f7fa24
3341$ git add a
3342$ git commit -m "Updated submodule a."
3343$ git push
3344-------------------------------------------------
3345
3346You have to run `git submodule update` after `git pull` if you want to update
3347submodules, too.
3348
3349Pitfalls with submodules
3350------------------------
3351
3352Always publish the submodule change before publishing the change to the
3353superproject that references it. If you forget to publish the submodule change,
3354others won't be able to clone the repository:
3355
3356-------------------------------------------------
3357$ cd ~/git/super/a
3358$ echo i added another line to this file >> a.txt
3359$ git commit -a -m "doing it wrong this time"
3360$ cd ..
3361$ git add a
3362$ git commit -m "Updated submodule a again."
3363$ git push
3364$ cd ~/git/cloned
3365$ git pull
3366$ git submodule update
3367error: pathspec '261dfac35cb99d380eb966e102c1197139f7fa24' did not match any file(s) known to git.
3368Did you forget to 'git add'?
3369Unable to checkout '261dfac35cb99d380eb966e102c1197139f7fa24' in submodule path 'a'
3370-------------------------------------------------
3371
3372You also should not rewind branches in a submodule beyond commits that were
3373ever recorded in any superproject.
3374
3375It's not safe to run `git submodule update` if you've made and committed
3376changes within a submodule without checking out a branch first. They will be
3377silently overwritten:
3378
3379-------------------------------------------------
3380$ cat a.txt
3381module a
3382$ echo line added from private2 >> a.txt
3383$ git commit -a -m "line added inside private2"
3384$ cd ..
3385$ git submodule update
3386Submodule path 'a': checked out 'd266b9873ad50488163457f025db7cdd9683d88b'
3387$ cd a
3388$ cat a.txt
3389module a
3390-------------------------------------------------
3391
3392NOTE: The changes are still visible in the submodule's reflog.
3393
3394This is not the case if you did not commit your changes.
3395
1c6045ff
BF
3396[[low-level-operations]]
3397Low-level git operations
3398========================
b181d57f 3399
1c6045ff
BF
3400Many of the higher-level commands were originally implemented as shell
3401scripts using a smaller core of low-level git commands. These can still
3402be useful when doing unusual things with git, or just as a way to
3403understand its inner workings.
b181d57f 3404
1bbf1c79
BF
3405[[object-manipulation]]
3406Object access and manipulation
3407------------------------------
3408
3409The gitlink:git-cat-file[1] command can show the contents of any object,
3410though the higher-level gitlink:git-show[1] is usually more useful.
3411
3412The gitlink:git-commit-tree[1] command allows constructing commits with
3413arbitrary parents and trees.
3414
3415A tree can be created with gitlink:git-write-tree[1] and its data can be
3416accessed by gitlink:git-ls-tree[1]. Two trees can be compared with
3417gitlink:git-diff-tree[1].
3418
3419A tag is created with gitlink:git-mktag[1], and the signature can be
3420verified by gitlink:git-verify-tag[1], though it is normally simpler to
3421use gitlink:git-tag[1] for both.
3422
e34caace 3423[[the-workflow]]
b181d57f
BF
3424The Workflow
3425------------
3426
1c6045ff
BF
3427High-level operations such as gitlink:git-commit[1],
3428gitlink:git-checkout[1] and git-reset[1] work by moving data between the
3429working tree, the index, and the object database. Git provides
3430low-level operations which perform each of these steps individually.
3431
b181d57f
BF
3432Generally, all "git" operations work on the index file. Some operations
3433work *purely* on the index file (showing the current state of the
1c6045ff
BF
3434index), but most operations move data between the index file and either
3435the database or the working directory. Thus there are four main
3436combinations:
b181d57f 3437
e34caace 3438[[working-directory-to-index]]
b181d57f
BF
3439working directory -> index
3440~~~~~~~~~~~~~~~~~~~~~~~~~~
3441
1c6045ff
BF
3442The gitlink:git-update-index[1] command updates the index with
3443information from the working directory. You generally update the
3444index information by just specifying the filename you want to update,
3445like so:
b181d57f
BF
3446
3447-------------------------------------------------
1c6045ff 3448$ git update-index filename
b181d57f
BF
3449-------------------------------------------------
3450
3451but to avoid common mistakes with filename globbing etc, the command
3452will not normally add totally new entries or remove old entries,
3453i.e. it will normally just update existing cache entries.
3454
3455To tell git that yes, you really do realize that certain files no
3456longer exist, or that new files should be added, you
3457should use the `--remove` and `--add` flags respectively.
3458
3459NOTE! A `--remove` flag does 'not' mean that subsequent filenames will
3460necessarily be removed: if the files still exist in your directory
3461structure, the index will be updated with their new status, not
3462removed. The only thing `--remove` means is that update-cache will be
3463considering a removed file to be a valid thing, and if the file really
3464does not exist any more, it will update the index accordingly.
3465
3466As a special case, you can also do `git-update-index --refresh`, which
3467will refresh the "stat" information of each index to match the current
3468stat information. It will 'not' update the object status itself, and
3469it will only update the fields that are used to quickly test whether
3470an object still matches its old backing store object.
3471
1c6045ff
BF
3472The previously introduced gitlink:git-add[1] is just a wrapper for
3473gitlink:git-update-index[1].
3474
e34caace 3475[[index-to-object-database]]
b181d57f
BF
3476index -> object database
3477~~~~~~~~~~~~~~~~~~~~~~~~
3478
3479You write your current index file to a "tree" object with the program
3480
3481-------------------------------------------------
1c6045ff 3482$ git write-tree
b181d57f
BF
3483-------------------------------------------------
3484
3485that doesn't come with any options - it will just write out the
3486current index into the set of tree objects that describe that state,
3487and it will return the name of the resulting top-level tree. You can
3488use that tree to re-generate the index at any time by going in the
3489other direction:
3490
e34caace 3491[[object-database-to-index]]
b181d57f
BF
3492object database -> index
3493~~~~~~~~~~~~~~~~~~~~~~~~
3494
3495You read a "tree" file from the object database, and use that to
3496populate (and overwrite - don't do this if your index contains any
3497unsaved state that you might want to restore later!) your current
3498index. Normal operation is just
3499
3500-------------------------------------------------
3501$ git-read-tree <sha1 of tree>
3502-------------------------------------------------
3503
3504and your index file will now be equivalent to the tree that you saved
3505earlier. However, that is only your 'index' file: your working
3506directory contents have not been modified.
3507
e34caace 3508[[index-to-working-directory]]
b181d57f
BF
3509index -> working directory
3510~~~~~~~~~~~~~~~~~~~~~~~~~~
3511
3512You update your working directory from the index by "checking out"
3513files. This is not a very common operation, since normally you'd just
3514keep your files updated, and rather than write to your working
3515directory, you'd tell the index files about the changes in your
3516working directory (i.e. `git-update-index`).
3517
3518However, if you decide to jump to a new version, or check out somebody
3519else's version, or just restore a previous tree, you'd populate your
3520index file with read-tree, and then you need to check out the result
3521with
3522
3523-------------------------------------------------
3524$ git-checkout-index filename
3525-------------------------------------------------
3526
3527or, if you want to check out all of the index, use `-a`.
3528
3529NOTE! git-checkout-index normally refuses to overwrite old files, so
3530if you have an old version of the tree already checked out, you will
3531need to use the "-f" flag ('before' the "-a" flag or the filename) to
3532'force' the checkout.
3533
3534
3535Finally, there are a few odds and ends which are not purely moving
3536from one representation to the other:
3537
e34caace 3538[[tying-it-all-together]]
b181d57f
BF
3539Tying it all together
3540~~~~~~~~~~~~~~~~~~~~~
3541
3542To commit a tree you have instantiated with "git-write-tree", you'd