三十二、git pull简介

本文整理自：

http://web.mit.edu/~mkgray/project/silk/root/afs/sipb/project/git/git-doc/git-pull.html 

http://www.cnblogs.com/lbsx/archive/2010/10/16/1853193.html

 在git中，我们可以通过git pull命令把服务器仓库的更新拉到本地仓库中。git pull相当于是从远程获取最新版本并merge到本地。

当git clone之后，直接git pull它会自动匹配一个正确的remote url

是因为在config文件中配置了以下内容：

1 [branch "master"]
2 remote = origin
3 merge = refs/heads/master

表明：

1.git处于master这个branch下时，默认的remote就是origin；

2.当在master这个brach下使用指定remote和merge的git pull时，使用默认的remote和merge。

 

但是对于自己建的项目，并用push到远程服务器上，并没有这块内容，需要自己配置。

如果直接运行git pull，会得到如此结果：

 

1 $ git pull
2 Password:
3 You asked me to pull without telling me which branch you
4 want to merge with, and 'branch.master.merge' in
5 your configuration file does not tell me, either. Please
6 specify which branch you want to use on the command line and
7  try again (e.g. 'git pull <repository> <refspec>').
8 See git-pull(1) for details.
9
10 If you often merge with the same branch, you may want to
11 use something like the following in your configuration file:
12
13 [branch "master"]
14 remote = <nickname>
15 merge = <remote-ref>
16
17 [remote "<nickname>"]
18 url = <url>
19 fetch = <refspec>
20
21 See git-config(1) for details.

在参考[2]中，有这样一段：

Note: at this point your repository is not setup to merge _from_ the remote branch when you type 'git pull'. You can either freshly 'clone' the repository (see "Developer checkout" below), or configure your current repository this way:

 

1 git remote add -f origin login@git.sv.gnu.org:/srv/git/project.git
2 git config branch.master.remote origin
3 git config branch.master.merge refs/heads/master   

 

 

因此通过git config进行如下配置：

1 $ git config branch.master.remote origin
2 $ git config branch.master.merge refs/heads/master

或者加上--global选项，对于全部项目都使用该配置。

高级内容请参考《git追踪分支》

语法

git pull [options] [<repository> [<refspec>…]]

 

DESCRIPTION

Incorporates changes from a remote repository into the current branch. In its default mode, git pull is shorthand for git fetch followed by git merge FETCH_HEAD.

More precisely, git pull runs git fetch with the given parameters and calls git merge to merge the retrieved branch heads into the current branch. With --rebase, it runs git rebase instead of git merge.

<repository> should be the name of a remote repository as passed to git-fetch(1). <refspec> can name an arbitrary remote ref (for example, the name of a tag) or even a collection of refs with corresponding remote-tracking branches (e.g., refs/heads/*:refs/remotes/origin/*), but usually it is the name of a branch in the remote repository.

Default values for <repository> and <branch> are read from the "remote" and "merge" configuration for the current branch as set by git-branch(1)--track.

Assume the following history exists and the current branch is "master":

A---B---C master on origin / D---E---F---G master

Then "git pull" will fetch and replay the changes from the remote master branch since it diverged from the local master (i.e., E) until its current commit (C) on top of master and record the result in a new commit along with the names of the two parent commits and a log message from the user describing the changes.

A---B---C remotes/origin/master / \ D---E---F---G---H master

See git-merge(1) for details, including how conflicts are presented and handled.

In git 1.7.0 or later, to cancel a conflicting merge, use git reset --merge. Warning: In older versions of git, running git pull with uncommitted changes is discouraged: while possible, it leaves you in a state that may be hard to back out of in the case of a conflict.

If any of the remote changes overlap with local uncommitted changes, the merge will be automatically cancelled and the work tree untouched. It is generally best to get any local changes in working order before pulling or stash them away with git-stash(1).

OPTIONS

Options meant for git pull itself and the underlying git merge must be given before the options meant for git fetch.

-q

--quiet

This is passed to both underlying git-fetch to squelch reporting of during transfer, and underlying git-merge to squelch output during merging.

-v

--verbose

Pass --verbose to git-fetch and git-merge.

--[no-]recurse-submodules[=yes|on-demand|no]

This option controls if new commits of all populated submodules should be fetched too (see git-config(1) and gitmodules(5)). That might be necessary to get the data needed for merging submodule commits, a feature git learned in 1.7.3. Notice that the result of a merge will not be checked out in the submodule, "git submodule update" has to be called afterwards to bring the work tree up to date with the merge result.

Options related to merging

 

--commit

--no-commit

Perform the merge and commit the result. This option can be used to override --no-commit.

With --no-commit perform the merge but pretend the merge failed and do not autocommit, to give the user a chance to inspect and further tweak the merge result before committing.

--edit

--no-edit

Invoke an editor before committing successful mechanical merge to further edit the auto-generated merge message, so that the user can explain and justify the merge. The --no-edit option can be used to accept the auto-generated message (this is generally discouraged). The --edit option is still useful if you are giving a draft message with the -m option from the command line and want to edit it in the editor.

Older scripts may depend on the historical behaviour of not allowing the user to edit the merge log message. They will see an editor opened when they run git merge. To make it easier to adjust such scripts to the updated behaviour, the environment variable GIT_MERGE_AUTOEDIT can be set to no at the beginning of them.

--ff

When the merge resolves as a fast-forward, only update the branch pointer, without creating a merge commit. This is the default behavior.

--no-ff

Create a merge commit even when the merge resolves as a fast-forward.

--ff-only

Refuse to merge and exit with a non-zero status unless the current HEAD is already up-to-date or the merge can be resolved as a fast-forward.

--log[=<n>]

--no-log

In addition to branch names, populate the log message with one-line descriptions from at most <n> actual commits that are being merged. See also git-fmt-merge-msg(1).

With --no-log do not list one-line descriptions from the actual commits being merged.

--stat

-n

--no-stat

Show a diffstat at the end of the merge. The diffstat is also controlled by the configuration option merge.stat.

With -n or --no-stat do not show a diffstat at the end of the merge.

--squash

--no-squash

Produce the working tree and index state as if a real merge happened (except for the merge information), but do not actually make a commit or move the HEAD, nor record $GIT_DIR/MERGE_HEAD to cause the next git commit command to create a merge commit. This allows you to create a single commit on top of the current branch whose effect is the same as merging another branch (or more in case of an octopus).

With --no-squash perform the merge and commit the result. This option can be used to override --squash.

-s <strategy>

--strategy=<strategy>

Use the given merge strategy; can be supplied more than once to specify them in the order they should be tried. If there is no -s option, a built-in list of strategies is used instead (git merge-recursive when merging a single head, git merge-octopus otherwise).

-X <option>

--strategy-option=<option>

Pass merge strategy specific option through to the merge strategy.

--summary

--no-summary

Synonyms to --stat and --no-stat; these are deprecated and will be removed in the future.

-q

--quiet

Operate quietly. Implies --no-progress.

-v

--verbose

Be verbose.

--progress

--no-progress

Turn progress on/off explicitly. If neither is specified, progress is shown if standard error is connected to a terminal. Note that not all merge strategies may support progress reporting.

--rebase

Rebase the current branch on top of the upstream branch after fetching. If there is a remote-tracking branch corresponding to the upstream branch and the upstream branch was rebased since last fetched, the rebase uses that information to avoid rebasing non-local changes.

See pull.rebase, branch.<name>.rebase and branch.autosetuprebase in git-config(1) if you want to make git pull always use --rebase instead of merging.

Note	This is a potentially dangerous mode of operation. It rewrites history, which does not bode well when you published that history already. Do not use this option unless you have read git-rebase(1) carefully.

--no-rebase

Override earlier --rebase.

Options related to fetching

 

--all

Fetch all remotes.

-a

--append

Append ref names and object names of fetched refs to the existing contents of .git/FETCH_HEAD. Without this option old data in .git/FETCH_HEADwill be overwritten.

--depth=<depth>

Deepen the history of a shallow repository created by git clone with --depth=<depth> option (see git-clone(1)) by the specified number of commits.

-f

--force

When git fetch is used with <rbranch>:<lbranch> refspec, it refuses to update the local branch <lbranch> unless the remote branch <rbranch> it fetches is a descendant of <lbranch>. This option overrides that check.

-k

--keep

Keep downloaded pack.

--no-tags

By default, tags that point at objects that are downloaded from the remote repository are fetched and stored locally. This option disables this automatic tag following. The default behavior for a remote may be specified with the remote.<name>.tagopt setting. See git-config(1).

-u

--update-head-ok

By default git fetch refuses to update the head which corresponds to the current branch. This flag disables the check. This is purely for the internal use for git pull to communicate with git fetch, and unless you are implementing your own Porcelain you are not supposed to use it.

--upload-pack <upload-pack>

When given, and the repository to fetch from is handled by git fetch-pack, --exec=<upload-pack> is passed to the command to specify non-default path for the command run on the other end.

--progress

Progress status is reported on the standard error stream by default when it is attached to a terminal, unless -q is specified. This flag forces progress status even if the standard error stream is not directed to a terminal.

<repository>

The "remote" repository that is the source of a fetch or pull operation. This parameter can be either a URL (see the section GIT URLSbelow) or the name of a remote (see the section REMOTES below).

<refspec>

The format of a <refspec> parameter is an optional plus +, followed by the source ref <src>, followed by a colon :, followed by the destination ref <dst>.

The remote ref that matches <src> is fetched, and if <dst> is not empty string, the local ref that matches it is fast-forwarded using <src>. If the optional plus + is used, the local ref is updated even if it does not result in a fast-forward update.

Note

If the remote branch from which you want to pull is modified in non-linear ways such as being rewound and rebased frequently, then a pull will attempt a merge with an older version of itself, likely conflict, and fail. It is under these conditions that you would want to use the + sign to indicate non-fast-forward updates will be needed. There is currently no easy way to determine or declare that a branch will be made available in a repository with this behavior; the pulling user simply must know this is the expected usage pattern for a branch.

Note

You never do your own development on branches that appear on the right hand side of a <refspec> colon on Pull: lines; they are to be updated by git fetch. If you intend to do development derived from a remote branch B, have a Pull:line to track it (i.e. Pull: B:remote-B), and have a separate branch my-B to do your development on top of it. The latter is created by git branch my-B remote-B (or its equivalent git checkout -b my-B remote-B). Run git fetch to keep track of the progress of the remote side, and when you see something new on the remote branch, merge it into your development branch with git pull . remote-B, while you are on my-B branch.

Note

There is a difference between listing multiple <refspec> directly on git pull command line and having multiple Pull:<refspec> lines for a <repository> and running git pull command without any explicit <refspec> parameters. <refspec> listed explicitly on the command line are always merged into the current branch after fetching. In other words, if you list more than one remote refs, you would be making an Octopus. While git pull run without any explicit <refspec> parameter takes default <refspec>s from Pull: lines, it merges only the first <refspec> found into the current branch, after fetching all the remote refs. This is because making an Octopus from remote refs is rarely done, while keeping track of multiple remote heads in one-go by fetching more than one is often useful.

Some short-cut notations are also supported.

• tag <tag> means the same as refs/tags/<tag>:refs/tags/<tag>; it requests fetching everything up to the given tag.

• A parameter <ref> without a colon is equivalent to <ref>: when pulling/fetching, so it merges <ref> into the current branch without storing the remote branch anywhere locally

GIT URLS

In general, URLs contain information about the transport protocol, the address of the remote server, and the path to the repository. Depending on the transport protocol, some of this information may be absent.

Git natively supports ssh, git, http, https, ftp, ftps, and rsync protocols. The following syntaxes may be used with them:

• ssh://[user@]host.xz[:port]/path/to/repo.git/

• git://host.xz[:port]/path/to/repo.git/

• http[s]://host.xz[:port]/path/to/repo.git/

• ftp[s]://host.xz[:port]/path/to/repo.git/

• rsync://host.xz/path/to/repo.git/

An alternative scp-like syntax may also be used with the ssh protocol:

• [user@]host.xz:path/to/repo.git/

The ssh and git protocols additionally support ~username expansion:

• ssh://[user@]host.xz[:port]/~[user]/path/to/repo.git/

• git://host.xz[:port]/~[user]/path/to/repo.git/

• [user@]host.xz:/~[user]/path/to/repo.git/

For local repositories, also supported by git natively, the following syntaxes may be used:

• /path/to/repo.git/

• file:///path/to/repo.git/

These two syntaxes are mostly equivalent, except when cloning, when the former implies --local option. See git-clone(1) for details.

When git doesn’t know how to handle a certain transport protocol, it attempts to use the remote-<transport> remote helper, if one exists. To explicitly request a remote helper, the following syntax may be used:

• < transport>::<address>

where <address> may be a path, a server and path, or an arbitrary URL-like string recognized by the specific remote helper being invoked. Seegit-remote-helpers(1) for details.

If there are a large number of similarly-named remote repositories and you want to use a different format for them (such that the URLs you use will be rewritten into URLs that work), you can create a configuration section of the form:

[url "<actual url base>"] insteadOf = <other url base>

For example, with this:

[url "git://git.host.xz/"] insteadOf = host.xz:/path/to/ insteadOf = work:

a URL like "work:repo.git" or like "host.xz:/path/to/repo.git" will be rewritten in any context that takes a URL to be "git://git.host.xz/repo.git".

If you want to rewrite URLs for push only, you can create a configuration section of the form:

[url "<actual url base>"] pushInsteadOf = <other url base>

For example, with this:

[url "ssh://example.org/"] pushInsteadOf = git://example.org/

a URL like "git://example.org/path/to/repo.git" will be rewritten to "ssh://example.org/path/to/repo.git" for pushes, but pulls will still use the original URL.

REMOTES

The name of one of the following can be used instead of a URL as <repository> argument:

• a remote in the git configuration file: $GIT_DIR/config,

• a file in the $GIT_DIR/remotes directory, or

• a file in the $GIT_DIR/branches directory.

All of these also allow you to omit the refspec from the command line because they each contain a refspec which git will use by default.

Named remote in configuration file

 

You can choose to provide the name of a remote which you had previously configured using git-remote(1), git-config(1) or even by a manual edit to the $GIT_DIR/config file. The URL of this remote will be used to access the repository. The refspec of this remote will be used by default when you do not provide a refspec on the command line. The entry in the config file would appear like this:

[remote "<name>"] url = <url> pushurl = <pushurl> push = <refspec> fetch = <refspec>

The <pushurl> is used for pushes only. It is optional and defaults to <url>.

Named file in $GIT_DIR/remotes

 

You can choose to provide the name of a file in $GIT_DIR/remotes. The URL in this file will be used to access the repository. The refspec in this file will be used as default when you do not provide a refspec on the command line. This file should have the following format:

URL: one of the above URL format Push: <refspec> Pull: <refspec>

Push: lines are used by git push and Pull: lines are used by git pull and git fetch. Multiple Push: and Pull: lines may be specified for additional branch mappings.

Named file in $GIT_DIR/branches

 

You can choose to provide the name of a file in $GIT_DIR/branches. The URL in this file will be used to access the repository. This file should have the following format:

        <url>#<head>

<url> is required; #<head> is optional.

Depending on the operation, git will use one of the following refspecs, if you don’t provide one on the command line. <branch> is the name of this file in $GIT_DIR/branches and <head> defaults to master.

git fetch uses:

        refs/heads/<head>:refs/heads/<branch>

git push uses:

        HEAD:refs/heads/<head>

MERGE STRATEGIES

The merge mechanism (git-merge and git-pull commands) allows the backend merge strategies to be chosen with -s option. Some strategies can also take their own options, which can be passed by giving -X<option> arguments to git-merge and/or git-pull.

resolve

This can only resolve two heads (i.e. the current branch and another branch you pulled from) using a 3-way merge algorithm. It tries to carefully detect criss-cross merge ambiguities and is considered generally safe and fast.

recursive

This can only resolve two heads using a 3-way merge algorithm. When there is more than one common ancestor that can be used for 3-way merge, it creates a merged tree of the common ancestors and uses that as the reference tree for the 3-way merge. This has been reported to result in fewer merge conflicts without causing mis-merges by tests done on actual merge commits taken from Linux 2.6 kernel development history. Additionally this can detect and handle merges involving renames. This is the default merge strategy when pulling or merging one branch.

The recursive strategy can take the following options:

ours

This option forces conflicting hunks to be auto-resolved cleanly by favoring our version. Changes from the other tree that do not conflict with our side are reflected to the merge result.

This should not be confused with the ours merge strategy, which does not even look at what the other tree contains at all. It discards everything the other tree did, declaring our history contains all that happened in it.

theirs

This is opposite of ours.

patience

With this option, merge-recursive spends a little extra time to avoid mismerges that sometimes occur due to unimportant matching lines (e.g., braces from distinct functions). Use this when the branches to be merged have diverged wildly. See also git-diff(1) --patience.

ignore-space-change

ignore-all-space

ignore-space-at-eol

Treats lines with the indicated type of whitespace change as unchanged for the sake of a three-way merge. Whitespace changes mixed with other changes to a line are not ignored. See also git-diff(1) -b, -w, and --ignore-space-at-eol.

• If their version only introduces whitespace changes to a line, our version is used;

• If our version introduces whitespace changes but their version includes a substantial change, their version is used;

• Otherwise, the merge proceeds in the usual way.

renormalize

This runs a virtual check-out and check-in of all three stages of a file when resolving a three-way merge. This option is meant to be used when merging branches with different clean filters or end-of-line normalization rules. See "Merging branches with differing checkin/checkout attributes" in gitattributes(5) for details.

no-renormalize

Disables the renormalize option. This overrides the merge.renormalize configuration variable.

rename-threshold=<n>

Controls the similarity threshold used for rename detection. See also git-diff(1) -M.

subtree[=<path>]

This option is a more advanced form of subtree strategy, where the strategy makes a guess on how two trees must be shifted to match with each other when merging. Instead, the specified path is prefixed (or stripped from the beginning) to make the shape of two trees to match.

octopus

This resolves cases with more than two heads, but refuses to do a complex merge that needs manual resolution. It is primarily meant to be used for bundling topic branch heads together. This is the default merge strategy when pulling or merging more than one branch.

ours

This resolves any number of heads, but the resulting tree of the merge is always that of the current branch head, effectively ignoring all changes from all other branches. It is meant to be used to supersede old development history of side branches. Note that this is different from the -Xours option to the recursive merge strategy.

subtree

This is a modified recursive strategy. When merging trees A and B, if B corresponds to a subtree of A, B is first adjusted to match the tree structure of A, instead of reading the trees at the same level. This adjustment is also done to the common ancestor tree.

DEFAULT BEHAVIOUR

Often people use git pull without giving any parameter. Traditionally, this has been equivalent to saying git pull origin. However, when configuration branch.<name>.remote is present while on branch <name>, that value is used instead of origin.

In order to determine what URL to use to fetch from, the value of the configuration remote.<origin>.url is consulted and if there is not any such variable, the value on URL: ` line in `$GIT_DIR/remotes/<origin> file is used.

In order to determine what remote branches to fetch (and optionally store in the remote-tracking branches) when the command is run without any refspec parameters on the command line, values of the configuration variable remote.<origin>.fetch are consulted, and if there aren’t any,$GIT_DIR/remotes/<origin> file is consulted and its `Pull: ` lines are used. In addition to the refspec formats described in the OPTIONS section, you can have a globbing refspec that looks like this:

refs/heads/*:refs/remotes/origin/*

A globbing refspec must have a non-empty RHS (i.e. must store what were fetched in remote-tracking branches), and its LHS and RHS must end with/*. The above specifies that all remote branches are tracked using remote-tracking branches in refs/remotes/origin/ hierarchy under the same name.

The rule to determine which remote branch to merge after fetching is a bit involved, in order not to break backward compatibility.

If explicit refspecs were given on the command line of git pull, they are all merged.

When no refspec was given on the command line, then git pull uses the refspec from the configuration or $GIT_DIR/remotes/<origin>. In such cases, the following rules apply:

1. If branch.<name>.merge configuration for the current branch <name> exists, that is the name of the branch at the remote site that is merged.

2. If the refspec is a globbing one, nothing is merged.

3. Otherwise the remote branch of the first refspec is merged.

EXAMPLES

• Update the remote-tracking branches for the repository you cloned from, then merge one of them into your current branch:

  $ git pull, git pull origin

  Normally the branch merged in is the HEAD of the remote repository, but the choice is determined by the branch.<name>.remote and branch.<name>.merge options; see git-config(1) for details.

• Merge into the current branch the remote branch next:

  $ git pull origin next

  This leaves a copy of next temporarily in FETCH_HEAD, but does not update any remote-tracking branches. Using remote-tracking branches, the same can be done by invoking fetch and merge:

  $ git fetch origin $ git merge origin/next

If you tried a pull which resulted in a complex conflicts and would want to start over, you can recover with git reset.

BUGS

Using --recurse-submodules can only fetch new commits in already checked out submodules right now. When e.g. upstream added a new submodule in the just fetched commits of the superproject the submodule itself can not be fetched, making it impossible to check out that submodule later without having to do a fetch again. This is expected to be fixed in a future git version.

SEE ALSO

git-fetch(1), git-merge(1), git-config(1)