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git fetch  

2015-03-18 10:26:41|  分类: 版本控制 |  标签: |举报 |字号 订阅

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一旦远程主机的版本库有了更新(Git术语叫做commit),需要将这些更新取回本地,这时就要用到git fetch命令。

$ git fetch <远程主机名>

上面命令将某个远程主机的更新,全部取回本地。
默认情况下,git fetch取回所有分支(branch)的更新。如果只想取回特定分支的更新,可以指定分支名。

$ git fetch <远程主机名> <分支名>

比如,取回origin主机的master分支。

$ git fetch origin master

所取回的更新,在本地主机上要用”远程主机名/分支名”的形式读取。比如origin主机的master,就要用origin/master读取。
git branch命令的-r选项,可以用来查看远程分支,-a选项查看所有分支。

$ git branch -r
origin/master

$ git branch -a
* master
  remotes/origin/master

上面命令表示,本地主机的当前分支是master,远程分支是origin/master。
有时git branch –a无法看到远程所有的分支,可以先执行 git fetch —prune; 然后执行 git branch –a 即可看到.
主要命令
我们可以通过git fetch -h查看其主要命令

git fetch -h
sage: git fetch [<options>] [<repository> [<refspec>...]]
  or: git fetch [<options>] <group>
  or: git fetch --multiple [<options>] [(<repository> | <group>)...]
  or: git fetch --all [<options>]

   -v, --verbose         be more verbose
   -q, --quiet           be more quiet
   --all                 fetch from all remotes
   -a, --append          append to .git/FETCH_HEAD instead of overwriting
   --upload-pack <path>  path to upload pack on remote end
   -f, --force           force overwrite of local branch
   -m, --multiple        fetch from multiple remotes
   -t, --tags            fetch all tags and associated objects
   -n                    do not fetch all tags (--no-tags)
   -p, --prune           prune remote-tracking branches no longer on remote
   --recurse-submodules[=<on-demand>]
                         control recursive fetching of submodules
   --dry-run             dry run
   -k, --keep            keep downloaded pack
   -u, --update-head-ok  allow updating of HEAD ref
   --progress            force progress reporting
   --depth <depth>       deepen history of shallow clone
   --unshallow           convert to a complete repository
   --update-shallow      accept refs that update .git/shallow

语法详解

通过git fetch --help可以看到git fetch的语法详解。

git-fetch - Download objects and refs from another repository

SYNOPSIS

git fetch [<options>] [<repository> [<refspec>…]]
git fetch [<options>] <group>
git fetch --multiple [<options>] [(<repository> | <group>)…]
git fetch --all [<options>]

DESCRIPTION

Fetches named heads or tags from one or more other repositories, along with the objects necessary to complete them.

The ref names and their object names of fetched refs are stored in .git/FETCH_HEAD. This information is left for a later merge operation done by git merge.

By default, tags are auto-followed. This means that when fetching from a remote, any tags on the remote that point to objects that exist in the local repository are fetched. The effect is to fetch tags that point at branches that you are interested in. This default behavior can be changed by using the --tags or --no-tags options, by configuring remote.<name>.tagopt, or by using a refspec that fetches tags explicitly.

git fetch can fetch from either a single named repository, or from several repositories at once if <group> is given and there is a remotes.<group> entry in the configuration file. (See git-config(1)).

When no remote is specified, by default the origin remote will be used, unless there’s an upstream branch configured for the current branch.

OPTIONS

--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_HEAD will be overwritten.

--depth=<depth>

Deepen or shorten the history of a shallow repository created by git clone with --depth=<depth> option (see git-clone(1)) to the specified number of commits from the tip of each remote branch history. Tags for the deepened commits are not fetched.

--unshallow

If the source repository is complete, convert a shallow repository to a complete one, removing all the limitations imposed by shallow repositories.

If the source repository is shallow, fetch as much as possible so that the current repository has the same history as the source repository.

--update-shallow

By default when fetching from a shallow repository, git fetch refuses refs that require updating .git/shallow. This option updates .git/shallow and accept such refs.

--dry-run

Show what would be done, without making any changes.

-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.

--multiple

Allow several <repository> and <group> arguments to be specified. No <refspec>s may be specified.

-p
--prune

After fetching, remove any remote-tracking references that no longer exist on the remote. Tags are not subject to pruning if they are fetched only because of the default tag auto-following or due to a --tags option. However, if tags are fetched due to an explicit refspec (either on the command line or in the remote configuration, for example if the remote was cloned with the --mirror option), then they are also subject to pruning.

如果上次从远程取到本地分支,在远程已经不再存在的话,该本地分支将被删除到。另外通过--tags

 default tag auto-following取到本地的分支不受此控制。但是通过explicit refspec取得的tags(比如在克隆时使用了--mirror参数)也受此控制

-n
--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).

-t
--tags

Fetch all tags from the remote (i.e., fetch remote tags refs/tags/* into local tags with the same name), in addition to whatever else would otherwise be fetched. Using this option alone does not subject tags to pruning, even if --prune is used (though tags may be pruned anyway if they are also the destination of an explicit refspec; see --prune).

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

This option controls if and under what conditions new commits of populated submodules should be fetched too. It can be used as a boolean option to completely disable recursion when set to no or to unconditionally recurse into all populated submodules when set to yes, which is the default when this option is used without any value. Use on-demand to only recurse into a populated submodule when the superproject retrieves a commit that updates the submodule’s reference to a commit that isn’t already in the local submodule clone.

--no-recurse-submodules

Disable recursive fetching of submodules (this has the same effect as using the --recurse-submodules=no option).

--submodule-prefix=<path>

Prepend <path> to paths printed in informative messages such as "Fetching submodule foo". This option is used internally when recursing over submodules.

--recurse-submodules-default=[yes|on-demand]

This option is used internally to temporarily provide a non-negative default value for the --recurse-submodules option. All other methods of configuring fetch’s submodule recursion (such as settings in gitmodules(5) and git-config(1)) override this option, as does specifying --[no-]recurse-submodules directly.

-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.

-q
--quiet

Pass --quiet to git-fetch-pack and silence any other internally used git commands. Progress is not reported to the standard error stream.

-v
--verbose

Be verbose.

--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 URLS below) or the name of a remote (see the section REMOTES below).

<group>

A name referring to a list of repositories as the value of remotes.<group> in the configuration file. (See git-config(1)).

<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 fetches that ref into FETCH_HEAD, and updates the remote-tracking branches (if any). 

示例1

$ git fetch origin +pu:pu maint:tmp

This updates (or creates, as necessary) branches pu and tmp in the local repository by fetching from the branches (respectively) pu and maint from the remote repository.
The pu branch will be updated even if it is does not fast-forward, because it is prefixed with a plus sign; tmp will not be.
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