1 .\"Generated by db2man.xsl. Don't modify this, modify the source.
10 .de Sp \" Vertical space (when we can't use .PP)
16 .ie \\n(.$>=3 .ne \\$3
22 git \- the stupid content tracker
26 \fIgit\fR [\-\-version] [\-\-exec\-path[=GIT_EXEC_PATH]] [\-\-help] COMMAND [ARGS]
31 \fIgit\fR is both a program and a directory content tracker system\&. The program \fIgit\fR is just a wrapper to reach the core git programs (or a potty if you like, as it's not exactly porcelain but still brings your stuff to the plumbing)\&.
37 prints the git suite version that the \fIgit\fR program came from\&.
41 prints the synopsis and a list of available commands\&. If a git command is named this option will bring up the man\-page for that command\&.
45 path to wherever your core git programs are installed\&. This can also be controlled by setting the GIT_EXEC_PATH environment variable\&. If no path is given \fIgit\fR will print the current setting and then exit\&.
47 .SH "NOT LEARNING CORE GIT COMMANDS"
50 This manual is intended to give complete background information and internal workings of git, which may be too much for most people\&. The [xref to anchor] section below contains much useful definition and clarification \- read that first\&.
53 If you are interested in using git to manage (version control) projects, use The Tutorial: \fItutorial.html\fR to get you started, and then Everyday GIT: \fIeveryday.html\fR as a guide to the minimum set of commands you need to know for day\-to\-day work\&. Most likely, that will get you started, and you can go a long way without knowing the low level details too much\&.
56 The Core tutorial: \fIcore-tutorial.html\fR document covers how things internally work\&.
59 If you are migrating from CVS, cvs migration: \fIcvs-migration.html\fR document may be helpful after you finish the tutorial\&.
62 After you get the general feel from the tutorial and this overview page, you may want to take a look at the howto: \fIhowto-index.html\fR documents\&.
64 .SH "CORE GIT COMMANDS"
67 If you are writing your own Porcelain, you need to be familiar with most of the low level commands \-\-\- I suggest starting from \fBgit\-update\-index\fR(1) and \fBgit\-read\-tree\fR(1)\&.
69 .SH "COMMANDS OVERVIEW"
72 The git commands can helpfully be split into those that manipulate the repository, the index and the files in the working tree, those that interrogate and compare them, and those that moves objects and references between repositories\&.
75 In addition, git itself comes with a spartan set of porcelain commands\&. They are usable but are not meant to compete with real Porcelains\&.
78 There are also some ancillary programs that can be viewed as useful aids for using the core commands but which are unlikely to be used by SCMs layered over git\&.
80 .SS "Manipulation commands"
84 Reads a "diff \-up1" or git generated patch file and applies it to the working tree\&.
87 \fBgit\-checkout\-index\fR(1)
88 Copy files from the index to the working tree\&.
91 \fBgit\-commit\-tree\fR(1)
92 Creates a new commit object\&.
95 \fBgit\-hash\-object\fR(1)
96 Computes the object ID from a file\&.
99 \fBgit\-index\-pack\fR(1)
100 Build pack idx file for an existing packed archive\&.
103 \fBgit\-init\-db\fR(1)
104 Creates an empty git object database, or reinitialize an existing one\&.
107 \fBgit\-merge\-index\fR(1)
108 Runs a merge for files needing merging\&.
112 Creates a tag object\&.
115 \fBgit\-pack\-objects\fR(1)
116 Creates a packed archive of objects\&.
119 \fBgit\-prune\-packed\fR(1)
120 Remove extra objects that are already in pack files\&.
123 \fBgit\-read\-tree\fR(1)
124 Reads tree information into the index\&.
127 \fBgit\-repo\-config\fR(1)
128 Get and set options in \&.git/config\&.
131 \fBgit\-unpack\-objects\fR(1)
132 Unpacks objects out of a packed archive\&.
135 \fBgit\-update\-index\fR(1)
136 Registers files in the working tree to the index\&.
139 \fBgit\-write\-tree\fR(1)
140 Creates a tree from the index\&.
142 .SS "Interrogation commands"
145 \fBgit\-cat\-file\fR(1)
146 Provide content or type/size information for repository objects\&.
149 \fBgit\-describe\fR(1)
150 Show the most recent tag that is reachable from a commit\&.
153 \fBgit\-diff\-index\fR(1)
154 Compares content and mode of blobs between the index and repository\&.
157 \fBgit\-diff\-files\fR(1)
158 Compares files in the working tree and the index\&.
161 \fBgit\-diff\-stages\fR(1)
162 Compares two "merge stages" in the index\&.
165 \fBgit\-diff\-tree\fR(1)
166 Compares the content and mode of blobs found via two tree objects\&.
169 \fBgit\-fsck\-objects\fR(1)
170 Verifies the connectivity and validity of the objects in the database\&.
173 \fBgit\-ls\-files\fR(1)
174 Information about files in the index and the working tree\&.
177 \fBgit\-ls\-tree\fR(1)
178 Displays a tree object in human readable form\&.
181 \fBgit\-merge\-base\fR(1)
182 Finds as good common ancestors as possible for a merge\&.
185 \fBgit\-name\-rev\fR(1)
186 Find symbolic names for given revs\&.
189 \fBgit\-pack\-redundant\fR(1)
190 Find redundant pack files\&.
193 \fBgit\-rev\-list\fR(1)
194 Lists commit objects in reverse chronological order\&.
197 \fBgit\-show\-index\fR(1)
198 Displays contents of a pack idx file\&.
201 \fBgit\-tar\-tree\fR(1)
202 Creates a tar archive of the files in the named tree object\&.
205 \fBgit\-unpack\-file\fR(1)
206 Creates a temporary file with a blob's contents\&.
210 Displays a git logical variable\&.
213 \fBgit\-verify\-pack\fR(1)
214 Validates packed git archive files\&.
217 In general, the interrogate commands do not touch the files in the working tree\&.
219 .SS "Synching repositories"
222 \fBgit\-clone\-pack\fR(1)
223 Clones a repository into the current repository (engine for ssh and local transport)\&.
226 \fBgit\-fetch\-pack\fR(1)
227 Updates from a remote repository (engine for ssh and local transport)\&.
230 \fBgit\-http\-fetch\fR(1)
231 Downloads a remote git repository via HTTP by walking commit chain\&.
234 \fBgit\-local\-fetch\fR(1)
235 Duplicates another git repository on a local system by walking commit chain\&.
238 \fBgit\-peek\-remote\fR(1)
239 Lists references on a remote repository using upload\-pack protocol (engine for ssh and local transport)\&.
242 \fBgit\-receive\-pack\fR(1)
243 Invoked by \fIgit\-send\-pack\fR to receive what is pushed to it\&.
246 \fBgit\-send\-pack\fR(1)
247 Pushes to a remote repository, intelligently\&.
250 \fBgit\-http\-push\fR(1)
251 Push missing objects using HTTP/DAV\&.
255 Restricted shell for GIT\-only SSH access\&.
258 \fBgit\-ssh\-fetch\fR(1)
259 Pulls from a remote repository over ssh connection by walking commit chain\&.
262 \fBgit\-ssh\-upload\fR(1)
263 Helper "server\-side" program used by git\-ssh\-fetch\&.
266 \fBgit\-update\-server\-info\fR(1)
267 Updates auxiliary information on a dumb server to help clients discover references and packs on it\&.
270 \fBgit\-upload\-pack\fR(1)
271 Invoked by \fIgit\-clone\-pack\fR and \fIgit\-fetch\-pack\fR to push what are asked for\&.
273 .SH "PORCELAIN-ISH COMMANDS"
277 Add paths to the index\&.
281 Apply patches from a mailbox, but cooler\&.
284 \fBgit\-applymbox\fR(1)
285 Apply patches from a mailbox, original version by Linus\&.
289 Find the change that introduced a bug by binary search\&.
293 Create and Show branches\&.
296 \fBgit\-checkout\fR(1)
297 Checkout and switch to a branch\&.
300 \fBgit\-cherry\-pick\fR(1)
301 Cherry\-pick the effect of an existing commit\&.
305 Clones a repository into a new directory\&.
309 Record changes to the repository\&.
313 Show changes between commits, commit and working tree, etc\&.
317 Download from a remote repository via various protocols\&.
320 \fBgit\-format\-patch\fR(1)
321 Prepare patches for e\-mail submission\&.
325 Print lines matching a pattern\&.
332 \fBgit\-ls\-remote\fR(1)
333 Shows references in a remote or local repository\&.
337 Grand unified merge driver\&.
341 Move or rename a file, a directory, or a symlink\&.
345 Fetch from and merge with a remote repository\&.
349 Update remote refs along with associated objects\&.
353 Rebase local commits to the updated upstream head\&.
357 Pack unpacked objects in a repository\&.
361 Reuse recorded resolution of conflicted merges\&.
365 Reset current HEAD to the specified state\&.
368 \fBgit\-resolve\fR(1)
373 Revert an existing commit\&.
376 \fBgit\-shortlog\fR(1)
377 Summarizes \fIgit log\fR output\&.
380 \fBgit\-show\-branch\fR(1)
381 Show branches and their commits\&.
385 Shows the working tree status\&.
388 \fBgit\-verify\-tag\fR(1)
389 Check the GPG signature of tag\&.
392 \fBgit\-whatchanged\fR(1)
393 Shows commit logs and differences they introduce\&.
395 .SH "ANCILLARY COMMANDS"
401 \fBgit\-applypatch\fR(1)
402 Apply one patch extracted from an e\-mail\&.
405 \fBgit\-archimport\fR(1)
406 Import an arch repository into git\&.
409 \fBgit\-convert\-objects\fR(1)
410 Converts old\-style git repository\&.
413 \fBgit\-cvsimport\fR(1)
414 Salvage your data out of another SCM people love to hate\&.
417 \fBgit\-cvsexportcommit\fR(1)
418 Export a single commit to a CVS checkout\&.
421 \fBgit\-lost\-found\fR(1)
422 Recover lost refs that luckily have not yet been pruned\&.
425 \fBgit\-merge\-one\-file\fR(1)
426 The standard helper program to use with git\-merge\-index\&.
430 Prunes all unreachable objects from the object database\&.
434 Hardlink common objects in local repositories\&.
437 \fBgit\-svnimport\fR(1)
438 Import a SVN repository into git\&.
441 \fBgit\-sh\-setup\fR(1)
442 Common git shell script setup code\&.
445 \fBgit\-symbolic\-ref\fR(1)
446 Read and modify symbolic refs\&.
450 An example script to create a tag object signed with GPG\&.
453 \fBgit\-update\-ref\fR(1)
454 Update the object name stored in a ref safely\&.
460 \fBgit\-check\-ref\-format\fR(1)
461 Make sure ref name is well formed\&.
465 Find commits not merged upstream\&.
468 \fBgit\-count\-objects\fR(1)
469 Count unpacked number of objects and their disk consumption\&.
473 A really simple server for git repositories\&.
476 \fBgit\-get\-tar\-commit\-id\fR(1)
477 Extract commit ID from an archive created using git\-tar\-tree\&.
480 \fBgit\-mailinfo\fR(1)
481 Extracts patch and authorship information from a single e\-mail message, optionally transliterating the commit message into utf\-8\&.
484 \fBgit\-mailsplit\fR(1)
485 A stupid program to split UNIX mbox format mailbox into individual pieces of e\-mail\&.
488 \fBgit\-patch\-id\fR(1)
489 Compute unique ID for a patch\&.
492 \fBgit\-parse\-remote\fR(1)
493 Routines to help parsing $GIT_DIR/remotes/ files\&.
496 \fBgit\-request\-pull\fR(1)
497 git\-request\-pull\&.
500 \fBgit\-rev\-parse\fR(1)
501 Pick out and massage parameters\&.
504 \fBgit\-send\-email\fR(1)
505 Send patch e\-mails out of "format\-patch \-\-mbox" output\&.
508 \fBgit\-symbolic\-ref\fR(1)
509 Read and modify symbolic refs\&.
512 \fBgit\-stripspace\fR(1)
513 Filter out empty lines\&.
515 .SH "COMMANDS NOT YET DOCUMENTED"
519 The gitk repository browser\&.
521 .SH "CONFIGURATION MECHANISM"
524 Starting from 0\&.99\&.9 (actually mid 0\&.99\&.8\&.GIT), \&.git/config file is used to hold per\-repository configuration options\&. It is a simple text file modelled after \&.ini format familiar to some people\&. Here is an example:
528 # A '#' or ';' character indicates a comment\&.
533 ; Don't trust file modes
538 name = "Junio C Hamano"
539 email = "junkio@twinsun\&.com"
542 Various commands read from the configuration file and adjust their operation accordingly\&.
544 .SH "IDENTIFIER TERMINOLOGY"
548 Indicates the object name for any type of object\&.
552 Indicates a blob object name\&.
556 Indicates a tree object name\&.
560 Indicates a commit object name\&.
564 Indicates a tree, commit or tag object name\&. A command that takes a <tree\-ish> argument ultimately wants to operate on a <tree> object but automatically dereferences <commit> and <tag> objects that point at a <tree>\&.
568 Indicates that an object type is required\&. Currently one of: blob, tree, commit, or tag\&.
572 Indicates a filename \- almost always relative to the root of the tree structure GIT_INDEX_FILE describes\&.
574 .SH "SYMBOLIC IDENTIFIERS"
577 Any git command accepting any <object> can also use the following symbolic notation:
581 indicates the head of the current branch (i\&.e\&. the contents of $GIT_DIR/HEAD)\&.
585 a valid tag \fIname\fR (i\&.e\&. the contents of $GIT_DIR/refs/tags/<tag>)\&.
589 a valid head \fIname\fR (i\&.e\&. the contents of $GIT_DIR/refs/heads/<head>)\&.
593 a valid snapshot \fIname\fR (i\&.e\&. the contents of $GIT_DIR/refs/snap/<snap>)\&.
595 .SH "FILE/DIRECTORY STRUCTURE"
598 Please see repository layout: \fIrepository-layout.html\fR document\&.
601 Higher level SCMs may provide and manage additional information in the $GIT_DIR\&.
606 Please see glossary: \fIglossary.html\fR document\&.
608 .SH "ENVIRONMENT VARIABLES"
611 Various git commands use the following environment variables:
613 .SS "The git Repository"
616 These environment variables apply to \fIall\fR core git commands\&. Nb: it is worth noting that they may be used/overridden by SCMS sitting above git so take care if using Cogito etc\&.
620 This environment allows the specification of an alternate index file\&. If not specified, the default of $GIT_DIR/index is used\&.
623 \fIGIT_OBJECT_DIRECTORY\fR
624 If the object storage directory is specified via this environment variable then the sha1 directories are created underneath \- otherwise the default $GIT_DIR/objects directory is used\&.
627 \fIGIT_ALTERNATE_OBJECT_DIRECTORIES\fR
628 Due to the immutable nature of git objects, old objects can be archived into shared, read\-only directories\&. This variable specifies a ":" separated list of git object directories which can be used to search for git objects\&. New objects will not be written to these directories\&.
632 If the \fIGIT_DIR\fR environment variable is set then it specifies a path to use instead of the default \&.git for the base of the repository\&.
637 \fIGIT_AUTHOR_NAME\fR, \fIGIT_AUTHOR_EMAIL\fR, \fIGIT_AUTHOR_DATE\fR, \fIGIT_COMMITTER_NAME\fR, \fIGIT_COMMITTER_EMAIL\fR
638 see \fBgit\-commit\-tree\fR(1)
643 \fIGIT_DIFF_OPTS\fR, \fIGIT_EXTERNAL_DIFF\fR
644 see the "generating patches" section in : \fBgit\-diff\-index\fR(1); \fBgit\-diff\-files\fR(1); \fBgit\-diff\-tree\fR(1)
649 "git" can mean anything, depending on your mood\&.
653 random three\-letter combination that is pronounceable, and not actually used by any common UNIX command\&. The fact that it is a mispronunciation of "get" may or may not be relevant\&.
656 stupid\&. contemptible and despicable\&. simple\&. Take your pick from the dictionary of slang\&.
659 "global information tracker": you're in a good mood, and it actually works for you\&. Angels sing, and a light suddenly fills the room\&.
662 "goddamn idiotic truckload of sh*t": when it breaks
666 This is a stupid (but extremely fast) directory content manager\&. It doesn't do a whole lot, but what it \fIdoes\fR do is track directory contents efficiently\&.
669 There are two object abstractions: the "object database", and the "current directory cache" aka "index"\&.
671 .SS "The Object Database"
674 The object database is literally just a content\-addressable collection of objects\&. All objects are named by their content, which is approximated by the SHA1 hash of the object itself\&. Objects may refer to other objects (by referencing their SHA1 hash), and so you can build up a hierarchy of objects\&.
677 All objects have a statically determined "type" aka "tag", which is determined at object creation time, and which identifies the format of the object (i\&.e\&. how it is used, and how it can refer to other objects)\&. There are currently four different object types: "blob", "tree", "commit" and "tag"\&.
680 A "blob" object cannot refer to any other object, and is, like the type implies, a pure storage object containing some user data\&. It is used to actually store the file data, i\&.e\&. a blob object is associated with some particular version of some file\&.
683 A "tree" object is an object that ties one or more "blob" objects into a directory structure\&. In addition, a tree object can refer to other tree objects, thus creating a directory hierarchy\&.
686 A "commit" object ties such directory hierarchies together into a DAG of revisions \- each "commit" is associated with exactly one tree (the directory hierarchy at the time of the commit)\&. In addition, a "commit" refers to one or more "parent" commit objects that describe the history of how we arrived at that directory hierarchy\&.
689 As a special case, a commit object with no parents is called the "root" object, and is the point of an initial project commit\&. Each project must have at least one root, and while you can tie several different root objects together into one project by creating a commit object which has two or more separate roots as its ultimate parents, that's probably just going to confuse people\&. So aim for the notion of "one root object per project", even if git itself does not enforce that\&.
692 A "tag" object symbolically identifies and can be used to sign other objects\&. It contains the identifier and type of another object, a symbolic name (of course!) and, optionally, a signature\&.
695 Regardless of object type, all objects share the following characteristics: they are all deflated with zlib, and have a header that not only specifies their type, but also provides size information about the data in the object\&. It's worth noting that the SHA1 hash that is used to name the object is the hash of the original data plus this header, so sha1sum \fIfile\fR does not match the object name for \fIfile\fR\&. (Historical note: in the dawn of the age of git the hash was the sha1 of the \fIcompressed\fR object\&.)
698 As a result, the general consistency of an object can always be tested independently of the contents or the type of the object: all objects can be validated by verifying that (a) their hashes match the content of the file and (b) the object successfully inflates to a stream of bytes that forms a sequence of <ascii type without space> + <space> + <ascii decimal size> + <byte\\0> + <binary object data>\&.
701 The structured objects can further have their structure and connectivity to other objects verified\&. This is generally done with the git\-fsck\-objects program, which generates a full dependency graph of all objects, and verifies their internal consistency (in addition to just verifying their superficial consistency through the hash)\&.
704 The object types in some more detail:
709 A "blob" object is nothing but a binary blob of data, and doesn't refer to anything else\&. There is no signature or any other verification of the data, so while the object is consistent (it \fIis\fR indexed by its sha1 hash, so the data itself is certainly correct), it has absolutely no other attributes\&. No name associations, no permissions\&. It is purely a blob of data (i\&.e\&. normally "file contents")\&.
712 In particular, since the blob is entirely defined by its data, if two files in a directory tree (or in multiple different versions of the repository) have the same contents, they will share the same blob object\&. The object is totally independent of its location in the directory tree, and renaming a file does not change the object that file is associated with in any way\&.
715 A blob is typically created when \fBgit\-update\-index\fR(1) is run, and its data can be accessed by \fBgit\-cat\-file\fR(1)\&.
720 The next hierarchical object type is the "tree" object\&. A tree object is a list of mode/name/blob data, sorted by name\&. Alternatively, the mode data may specify a directory mode, in which case instead of naming a blob, that name is associated with another TREE object\&.
723 Like the "blob" object, a tree object is uniquely determined by the set contents, and so two separate but identical trees will always share the exact same object\&. This is true at all levels, i\&.e\&. it's true for a "leaf" tree (which does not refer to any other trees, only blobs) as well as for a whole subdirectory\&.
726 For that reason a "tree" object is just a pure data abstraction: it has no history, no signatures, no verification of validity, except that since the contents are again protected by the hash itself, we can trust that the tree is immutable and its contents never change\&.
729 So you can trust the contents of a tree to be valid, the same way you can trust the contents of a blob, but you don't know where those contents \fIcame\fR from\&.
732 Side note on trees: since a "tree" object is a sorted list of "filename+content", you can create a diff between two trees without actually having to unpack two trees\&. Just ignore all common parts, and your diff will look right\&. In other words, you can effectively (and efficiently) tell the difference between any two random trees by O(n) where "n" is the size of the difference, rather than the size of the tree\&.
735 Side note 2 on trees: since the name of a "blob" depends entirely and exclusively on its contents (i\&.e\&. there are no names or permissions involved), you can see trivial renames or permission changes by noticing that the blob stayed the same\&. However, renames with data changes need a smarter "diff" implementation\&.
738 A tree is created with \fBgit\-write\-tree\fR(1) and its data can be accessed by \fBgit\-ls\-tree\fR(1)\&. Two trees can be compared with \fBgit\-diff\-tree\fR(1)\&.
743 The "commit" object is an object that introduces the notion of history into the picture\&. In contrast to the other objects, it doesn't just describe the physical state of a tree, it describes how we got there, and why\&.
746 A "commit" is defined by the tree\-object that it results in, the parent commits (zero, one or more) that led up to that point, and a comment on what happened\&. Again, a commit is not trusted per se: the contents are well\-defined and "safe" due to the cryptographically strong signatures at all levels, but there is no reason to believe that the tree is "good" or that the merge information makes sense\&. The parents do not have to actually have any relationship with the result, for example\&.
749 Note on commits: unlike real SCM's, commits do not contain rename information or file mode change information\&. All of that is implicit in the trees involved (the result tree, and the result trees of the parents), and describing that makes no sense in this idiotic file manager\&.
752 A commit is created with \fBgit\-commit\-tree\fR(1) and its data can be accessed by \fBgit\-cat\-file\fR(1)\&.
757 An aside on the notion of "trust"\&. Trust is really outside the scope of "git", but it's worth noting a few things\&. First off, since everything is hashed with SHA1, you \fIcan\fR trust that an object is intact and has not been messed with by external sources\&. So the name of an object uniquely identifies a known state \- just not a state that you may want to trust\&.
760 Furthermore, since the SHA1 signature of a commit refers to the SHA1 signatures of the tree it is associated with and the signatures of the parent, a single named commit specifies uniquely a whole set of history, with full contents\&. You can't later fake any step of the way once you have the name of a commit\&.
763 So to introduce some real trust in the system, the only thing you need to do is to digitally sign just \fIone\fR special note, which includes the name of a top\-level commit\&. Your digital signature shows others that you trust that commit, and the immutability of the history of commits tells others that they can trust the whole history\&.
766 In other words, you can easily validate a whole archive by just sending out a single email that tells the people the name (SHA1 hash) of the top commit, and digitally sign that email using something like GPG/PGP\&.
769 To assist in this, git also provides the tag object...
774 Git provides the "tag" object to simplify creating, managing and exchanging symbolic and signed tokens\&. The "tag" object at its simplest simply symbolically identifies another object by containing the sha1, type and symbolic name\&.
777 However it can optionally contain additional signature information (which git doesn't care about as long as there's less than 8k of it)\&. This can then be verified externally to git\&.
780 Note that despite the tag features, "git" itself only handles content integrity; the trust framework (and signature provision and verification) has to come from outside\&.
783 A tag is created with \fBgit\-mktag\fR(1), its data can be accessed by \fBgit\-cat\-file\fR(1), and the signature can be verified by \fBgit\-verify\-tag\fR(1)\&.
785 .SH "THE "INDEX" AKA "CURRENT DIRECTORY CACHE""
788 The index is a simple binary file, which contains an efficient representation of a virtual directory content at some random time\&. It does so by a simple array that associates a set of names, dates, permissions and content (aka "blob") objects together\&. The cache is always kept ordered by name, and names are unique (with a few very specific rules) at any point in time, but the cache has no long\-term meaning, and can be partially updated at any time\&.
791 In particular, the index certainly does not need to be consistent with the current directory contents (in fact, most operations will depend on different ways to make the index \fInot\fR be consistent with the directory hierarchy), but it has three very important attributes:
794 \fI(a) it can re\-generate the full state it caches (not just the directory structure: it contains pointers to the "blob" objects so that it can regenerate the data too)\fR
797 As a special case, there is a clear and unambiguous one\-way mapping from a current directory cache to a "tree object", which can be efficiently created from just the current directory cache without actually looking at any other data\&. So a directory cache at any one time uniquely specifies one and only one "tree" object (but has additional data to make it easy to match up that tree object with what has happened in the directory)
800 \fI(b) it has efficient methods for finding inconsistencies between that cached state ("tree object waiting to be instantiated") and the current state\&.\fR
803 \fI(c) it can additionally efficiently represent information about merge conflicts between different tree objects, allowing each pathname to be associated with sufficient information about the trees involved that you can create a three\-way merge between them\&.\fR
806 Those are the three ONLY things that the directory cache does\&. It's a cache, and the normal operation is to re\-generate it completely from a known tree object, or update/compare it with a live tree that is being developed\&. If you blow the directory cache away entirely, you generally haven't lost any information as long as you have the name of the tree that it described\&.
809 At the same time, the index is at the same time also the staging area for creating new trees, and creating a new tree always involves a controlled modification of the index file\&. In particular, the index file can have the representation of an intermediate tree that has not yet been instantiated\&. So the index can be thought of as a write\-back cache, which can contain dirty information that has not yet been written back to the backing store\&.
814 Generally, all "git" operations work on the index file\&. Some operations work \fIpurely\fR on the index file (showing the current state of the index), but most operations move data to and from the index file\&. Either from the database or from the working directory\&. Thus there are four main combinations:
816 .SS "1) working directory -> index"
819 You update the index with information from the working directory with the \fBgit\-update\-index\fR(1) command\&. You generally update the index information by just specifying the filename you want to update, like so:
822 git\-update\-index filename
826 but to avoid common mistakes with filename globbing etc, the command will not normally add totally new entries or remove old entries, i\&.e\&. it will normally just update existing cache entries\&.
829 To tell git that yes, you really do realize that certain files no longer exist, or that new files should be added, you should use the \-\-remove and \-\-add flags respectively\&.
832 NOTE! A \-\-remove flag does \fInot\fR mean that subsequent filenames will necessarily be removed: if the files still exist in your directory structure, the index will be updated with their new status, not removed\&. The only thing \-\-remove means is that update\-cache will be considering a removed file to be a valid thing, and if the file really does not exist any more, it will update the index accordingly\&.
835 As a special case, you can also do git\-update\-index \-\-refresh, which will refresh the "stat" information of each index to match the current stat information\&. It will \fInot\fR update the object status itself, and it will only update the fields that are used to quickly test whether an object still matches its old backing store object\&.
837 .SS "2) index -> object database"
840 You write your current index file to a "tree" object with the program
847 that doesn't come with any options \- it will just write out the current index into the set of tree objects that describe that state, and it will return the name of the resulting top\-level tree\&. You can use that tree to re\-generate the index at any time by going in the other direction:
849 .SS "3) object database -> index"
852 You read a "tree" file from the object database, and use that to populate (and overwrite \- don't do this if your index contains any unsaved state that you might want to restore later!) your current index\&. Normal operation is just
855 git\-read\-tree <sha1 of tree>
859 and your index file will now be equivalent to the tree that you saved earlier\&. However, that is only your \fIindex\fR file: your working directory contents have not been modified\&.
861 .SS "4) index -> working directory"
864 You update your working directory from the index by "checking out" files\&. This is not a very common operation, since normally you'd just keep your files updated, and rather than write to your working directory, you'd tell the index files about the changes in your working directory (i\&.e\&. git\-update\-index)\&.
867 However, if you decide to jump to a new version, or check out somebody else's version, or just restore a previous tree, you'd populate your index file with read\-tree, and then you need to check out the result with
870 git\-checkout\-index filename
874 or, if you want to check out all of the index, use \-a\&.
877 NOTE! git\-checkout\-index normally refuses to overwrite old files, so if you have an old version of the tree already checked out, you will need to use the "\-f" flag (\fIbefore\fR the "\-a" flag or the filename) to \fIforce\fR the checkout\&.
880 Finally, there are a few odds and ends which are not purely moving from one representation to the other:
882 .SS "5) Tying it all together"
885 To commit a tree you have instantiated with "git\-write\-tree", you'd create a "commit" object that refers to that tree and the history behind it \- most notably the "parent" commits that preceded it in history\&.
888 Normally a "commit" has one parent: the previous state of the tree before a certain change was made\&. However, sometimes it can have two or more parent commits, in which case we call it a "merge", due to the fact that such a commit brings together ("merges") two or more previous states represented by other commits\&.
891 In other words, while a "tree" represents a particular directory state of a working directory, a "commit" represents that state in "time", and explains how we got there\&.
894 You create a commit object by giving it the tree that describes the state at the time of the commit, and a list of parents:
897 git\-commit\-tree <tree> \-p <parent> [\-p <parent2> \&.\&.]
901 and then giving the reason for the commit on stdin (either through redirection from a pipe or file, or by just typing it at the tty)\&.
904 git\-commit\-tree will return the name of the object that represents that commit, and you should save it away for later use\&. Normally, you'd commit a new HEAD state, and while git doesn't care where you save the note about that state, in practice we tend to just write the result to the file pointed at by \&.git/HEAD, so that we can always see what the last committed state was\&.
907 Here is an ASCII art by Jon Loeliger that illustrates how various pieces fit together\&.
917 +\-\-\-\-\-\-\-\-\-\-\-+
921 +\-\-\-\-\-\-\-\-\-\-\-+
928 +\-\-\-\-\-\-\-\-\-\-\-+
931 +\-\-\-\-\-\-\-\-\-\-\-+
935 checkout\-index \-u | | checkout\-index
938 +\-\-\-\-\-\-\-\-\-\-\-+
941 +\-\-\-\-\-\-\-\-\-\-\-+
943 .SS "6) Examining the data"
946 You can examine the data represented in the object database and the index with various helper tools\&. For every object, you can use \fBgit\-cat\-file\fR(1) to examine details about the object:
949 git\-cat\-file \-t <objectname>
953 shows the type of the object, and once you have the type (which is usually implicit in where you find the object), you can use
956 git\-cat\-file blob|tree|commit|tag <objectname>
960 to show its contents\&. NOTE! Trees have binary content, and as a result there is a special helper for showing that content, called git\-ls\-tree, which turns the binary content into a more easily readable form\&.
963 It's especially instructive to look at "commit" objects, since those tend to be small and fairly self\-explanatory\&. In particular, if you follow the convention of having the top commit name in \&.git/HEAD, you can do
966 git\-cat\-file commit HEAD
970 to see what the top commit was\&.
972 .SS "7) Merging multiple trees"
975 Git helps you do a three\-way merge, which you can expand to n\-way by repeating the merge procedure arbitrary times until you finally "commit" the state\&. The normal situation is that you'd only do one three\-way merge (two parents), and commit it, but if you like to, you can do multiple parents in one go\&.
978 To do a three\-way merge, you need the two sets of "commit" objects that you want to merge, use those to find the closest common parent (a third "commit" object), and then use those commit objects to find the state of the directory ("tree" object) at these points\&.
981 To get the "base" for the merge, you first look up the common parent of two commits with
984 git\-merge\-base <commit1> <commit2>
988 which will return you the commit they are both based on\&. You should now look up the "tree" objects of those commits, which you can easily do with (for example)
991 git\-cat\-file commit <commitname> | head \-1
995 since the tree object information is always the first line in a commit object\&.
998 Once you know the three trees you are going to merge (the one "original" tree, aka the common case, and the two "result" trees, aka the branches you want to merge), you do a "merge" read into the index\&. This will complain if it has to throw away your old index contents, so you should make sure that you've committed those \- in fact you would normally always do a merge against your last commit (which should thus match what you have in your current index anyway)\&.
1004 git\-read\-tree \-m \-u <origtree> <yourtree> <targettree>
1008 which will do all trivial merge operations for you directly in the index file, and you can just write the result out with git\-write\-tree\&.
1011 Historical note\&. We did not have \-u facility when this section was first written, so we used to warn that the merge is done in the index file, not in your working tree, and your working tree will not match your index after this step\&. This is no longer true\&. The above command, thanks to \-u option, updates your working tree with the merge results for paths that have been trivially merged\&.
1013 .SS "8) Merging multiple trees, continued"
1016 Sadly, many merges aren't trivial\&. If there are files that have been added\&.moved or removed, or if both branches have modified the same file, you will be left with an index tree that contains "merge entries" in it\&. Such an index tree can \fINOT\fR be written out to a tree object, and you will have to resolve any such merge clashes using other tools before you can write out the result\&.
1019 You can examine such index state with git\-ls\-files \-\-unmerged command\&. An example:
1022 $ git\-read\-tree \-m $orig HEAD $target
1023 $ git\-ls\-files \-\-unmerged
1024 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello\&.c
1025 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello\&.c
1026 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello\&.c
1028 Each line of the git\-ls\-files \-\-unmerged output begins with the blob mode bits, blob SHA1, \fIstage number\fR, and the filename\&. The \fIstage number\fR is git's way to say which tree it came from: stage 1 corresponds to $orig tree, stage 2 HEAD tree, and stage3 $target tree\&.
1031 Earlier we said that trivial merges are done inside git\-read\-tree \-m\&. For example, if the file did not change from $orig to HEAD nor $target, or if the file changed from $orig to HEAD and $orig to $target the same way, obviously the final outcome is what is in HEAD\&. What the above example shows is that file hello\&.c was changed from $orig to HEAD and $orig to $target in a different way\&. You could resolve this by running your favorite 3\-way merge program, e\&.g\&. diff3 or merge, on the blob objects from these three stages yourself, like this:
1034 $ git\-cat\-file blob 263414f\&.\&.\&. >hello\&.c~1
1035 $ git\-cat\-file blob 06fa6a2\&.\&.\&. >hello\&.c~2
1036 $ git\-cat\-file blob cc44c73\&.\&.\&. >hello\&.c~3
1037 $ merge hello\&.c~2 hello\&.c~1 hello\&.c~3
1039 This would leave the merge result in hello\&.c~2 file, along with conflict markers if there are conflicts\&. After verifying the merge result makes sense, you can tell git what the final merge result for this file is by:
1042 mv \-f hello\&.c~2 hello\&.c
1043 git\-update\-index hello\&.c
1047 When a path is in unmerged state, running git\-update\-index for that path tells git to mark the path resolved\&.
1050 The above is the description of a git merge at the lowest level, to help you understand what conceptually happens under the hood\&. In practice, nobody, not even git itself, uses three git\-cat\-file for this\&. There is git\-merge\-index program that extracts the stages to temporary files and calls a "merge" script on it:
1053 git\-merge\-index git\-merge\-one\-file hello\&.c
1057 and that is what higher level git resolve is implemented with\&.
1063 git's founding father is Linus Torvalds <torvalds@osdl\&.org>\&.
1066 The current git nurse is Junio C Hamano <junkio@cox\&.net>\&.
1069 The git potty was written by Andres Ericsson <ae@op5\&.se>\&.
1072 General upbringing is handled by the git\-list <git@vger\&.kernel\&.org>\&.
1078 The documentation for git suite was started by David Greaves <david@dgreaves\&.com>, and later enhanced greatly by the contributors on the git\-list <git@vger\&.kernel\&.org>\&.
1083 Part of the \fBgit\fR(7) suite
projects / git.git / blob