git push -- 分支推送遠程

背景

基於上一篇git checkout -分支的新建、git commit --分支的提交和git merge —分支合併的背景，繼續瞭解使用的命令git push

自我認識

前幾篇已經根據我這次的需求介紹了會用到的命令以及每一次指針走向，git push 是把本地倉庫的更新推送到遠程服務器的倉庫。

這裏借花獻佛，瞭解一下git的整體架構，以及各部分相關的命令

前面已經把此次緊急需求的改動通過git add、git commit提交到了本地倉庫，最後一步就是同步到遠程倉庫。
這裏你也可以清楚看到git pull和git fetch的大致區別

常用的命令有：

git push origin master:master //提交本地分支master到作爲遠程master分支
git push origin :test // 刪除遠程的test分支，本地保留

文檔介紹

NAME
git-push - Update remote refs along with associated objects

SYNOPSIS
git push [–all | --mirror | --tags] [–follow-tags] [–atomic] [-n | --dry-run] [–receive-pack=]
[–repo=] [-f | --force] [-d | --delete] [–prune] [-v | --verbose]
[-u | --set-upstream] [-o | --push-option=]
[–[no-]signed|–signed=(true|false|if-asked)]
[–force-with-lease[=[:]]]
[–no-verify] [ […​]]
DESCRIPTION
Updates remote refs using local refs, while sending objects necessary to complete the given refs.

You can make interesting things happen to a repository every time you push into it, by setting up hooks there. See documentation for git-receive-pack[1].

When the command line does not specify where to push with the argument, branch.*.remote configuration for the current branch is consulted to determine where to push. If the configuration is missing, it defaults to origin.

When the command line does not specify what to push with … arguments or --all, --mirror, --tags options, the command finds the default by consulting remote.*.push configuration, and if it is not found, honors push.default configuration to decide what to push (See git-config[1] for the meaning of push.default).

When neither the command-line nor the configuration specify what to push, the default behavior is used, which corresponds to the simple value for push.default: the current branch is pushed to the corresponding upstream branch, but as a safety measure, the push is aborted if the upstream branch does not have the same name as the local one.

OPTIONS

The 「remote」 repository that is destination of a push 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).

…​
Specify what destination ref to update with what source object. The format of a parameter is an optional plus +, followed by the source object , followed by a colon :, followed by the destination ref .

The is often the name of the branch you would want to push, but it can be any arbitrary 「SHA-1 expression」, such as master~4 or HEAD (see gitrevisions[7]).

The tells which ref on the remote side is updated with this push. Arbitrary expressions cannot be used here, an actual ref must be named. If git push [] without any argument is set to update some ref at the destination with with remote..push configuration variable, : part can be omitted—​such a push will update a ref that normally updates without any on the command line. Otherwise, missing : means to update the same ref as the .

If doesn’t start with refs/ (e.g. refs/heads/master) we will try to infer where in refs/* on the destination it belongs based on the type of being pushed and whether is ambiguous.

If unambiguously refers to a ref on the remote, then push to that ref.

If resolves to a ref starting with refs/heads/ or refs/tags/, then prepend that to .

Other ambiguity resolutions might be added in the future, but for now any other cases will error out with an error indicating what we tried, and depending on the advice.pushUnqualifiedRefname configuration (see git-config[1]) suggest what refs/ namespace you may have wanted to push to.

The object referenced by is used to update the reference on the remote side. Whether this is allowed depends on where in refs/* the reference lives as described in detail below, in those sections 「update」 means any modifications except deletes, which as noted after the next few sections are treated differently.

The refs/heads/* namespace will only accept commit objects, and updates only if they can be fast-forwarded.

The refs/tags/* namespace will accept any kind of object (as commits, trees and blobs can be tagged), and any updates to them will be rejected.

It’s possible to push any type of object to any namespace outside of refs/{tags,heads}/. In the case of tags and commits, these will be treated as if they were the commits inside refs/heads/ for the purposes of whether the update is allowed.

I.e. a fast-forward of commits and tags outside refs/{tags,heads}/* is allowed, even in cases where what’s being fast-forwarded is not a commit, but a tag object which happens to point to a new commit which is a fast-forward of the commit the last tag (or commit) it’s replacing. Replacing a tag with an entirely different tag is also allowed, if it points to the same commit, as well as pushing a peeled tag, i.e. pushing the commit that existing tag object points to, or a new tag object which an existing commit points to.

Tree and blob objects outside of refs/{tags,heads}/* will be treated the same way as if they were inside refs/tags/*, any update of them will be rejected.

All of the rules described above about what’s not allowed as an update can be overridden by adding an the optional leading + to a refspec (or using --force command line option). The only exception to this is that no amount of forcing will make the refs/heads/* namespace accept a non-commit object. Hooks and configuration can also override or amend these rules, see e.g. receive.denyNonFastForwards in git-config[1] and pre-receive and update in githooks[5].

Pushing an empty allows you to delete the ref from the remote repository. Deletions are always accepted without a leading + in the refspec (or --force), except when forbidden by configuration or hooks. See receive.denyDeletes in git-config[1] and pre-receive and update in githooks[5].

The special refspec : (or +: to allow non-fast-forward updates) directs Git to push 「matching」 branches: for every branch that exists on the local side, the remote side is updated if a branch of the same name already exists on the remote side.

tag means the same as refs/tags/:refs/tags/.

–all
Push all branches (i.e. refs under refs/heads/); cannot be used with other .

–prune
Remove remote branches that don’t have a local counterpart. For example a remote branch tmp will be removed if a local branch with the same name doesn’t exist any more. This also respects refspecs, e.g. git push --prune remote refs/heads/:refs/tmp/ would make sure that remote refs/tmp/foo will be removed if refs/heads/foo doesn’t exist.

–mirror
Instead of naming each ref to push, specifies that all refs under refs/ (which includes but is not limited to refs/heads/, refs/remotes/, and refs/tags/) be mirrored to the remote repository. Newly created local refs will be pushed to the remote end, locally updated refs will be force updated on the remote end, and deleted refs will be removed from the remote end. This is the default if the configuration option remote..mirror is set.

-n
–dry-run
Do everything except actually send the updates.

–porcelain
Produce machine-readable output. The output status line for each ref will be tab-separated and sent to stdout instead of stderr. The full symbolic names of the refs will be given.

-d
–delete
All listed refs are deleted from the remote repository. This is the same as prefixing all refs with a colon.

–tags
All refs under refs/tags are pushed, in addition to refspecs explicitly listed on the command line.

–follow-tags
Push all the refs that would be pushed without this option, and also push annotated tags in refs/tags that are missing from the remote but are pointing at commit-ish that are reachable from the refs being pushed. This can also be specified with configuration variable push.followTags. For more information, see push.followTags in git-config[1].

–[no-]signed
–signed=(true|false|if-asked)
GPG-sign the push request to update refs on the receiving side, to allow it to be checked by the hooks and/or be logged. If false or --no-signed, no signing will be attempted. If true or --signed, the push will fail if the server does not support signed pushes. If set to if-asked, sign if and only if the server supports signed pushes. The push will also fail if the actual call to gpg --sign fails. See git-receive-pack[1] for the details on the receiving end.

–[no-]atomic
Use an atomic transaction on the remote side if available. Either all refs are updated, or on error, no refs are updated. If the server does not support atomic pushes the push will fail.

-o
–push-option=
Transmit the given string to the server, which passes them to the pre-receive as well as the post-receive hook. The given string must not contain a NUL or LF character. When multiple --push-option= are given, they are all sent to the other side in the order listed on the command line. When no --push-option= is given from the command line, the values of configuration variable push.pushOption are used instead.

–receive-pack=
–exec=
Path to the git-receive-pack program on the remote end. Sometimes useful when pushing to a remote repository over ssh, and you do not have the program in a directory on the default $PATH.

–[no-]force-with-lease
–force-with-lease=
–force-with-lease=:
Usually, 「git push」 refuses to update a remote ref that is not an ancestor of the local ref used to overwrite it.

This option overrides this restriction if the current value of the remote ref is the expected value. 「git push」 fails otherwise.

Imagine that you have to rebase what you have already published. You will have to bypass the 「must fast-forward」 rule in order to replace the history you originally published with the rebased history. If somebody else built on top of your original history while you are rebasing, the tip of the branch at the remote may advance with her commit, and blindly pushing with --force will lose her work.

This option allows you to say that you expect the history you are updating is what you rebased and want to replace. If the remote ref still points at the commit you specified, you can be sure that no other people did anything to the ref. It is like taking a 「lease」 on the ref without explicitly locking it, and the remote ref is updated only if the 「lease」 is still valid.

–force-with-lease alone, without specifying the details, will protect all remote refs that are going to be updated by requiring their current value to be the same as the remote-tracking branch we have for them.

–force-with-lease=, without specifying the expected value, will protect the named ref (alone), if it is going to be updated, by requiring its current value to be the same as the remote-tracking branch we have for it.

–force-with-lease=: will protect the named ref (alone), if it is going to be updated, by requiring its current value to be the same as the specified value (which is allowed to be different from the remote-tracking branch we have for the refname, or we do not even have to have such a remote-tracking branch when this form is used). If is the empty string, then the named ref must not already exist.

Note that all forms other than --force-with-lease=: that specifies the expected current value of the ref explicitly are still experimental and their semantics may change as we gain experience with this feature.

「–no-force-with-lease」 will cancel all the previous --force-with-lease on the command line.

A general note on safety: supplying this option without an expected value, i.e. as --force-with-lease or --force-with-lease= interacts very badly with anything that implicitly runs git fetch on the remote to be pushed to in the background, e.g. git fetch origin on your repository in a cronjob.

The protection it offers over --force is ensuring that subsequent changes your work wasn’t based on aren’t clobbered, but this is trivially defeated if some background process is updating refs in the background. We don’t have anything except the remote tracking info to go by as a heuristic for refs you’re expected to have seen & are willing to clobber.

If your editor or some other system is running git fetch in the background for you a way to mitigate this is to simply set up another remote:

git remote add origin-push $(git config remote.origin.url)
git fetch origin-push
Now when the background process runs git fetch origin the references on origin-push won’t be updated, and thus commands like:

git push --force-with-lease origin-push
Will fail unless you manually run git fetch origin-push. This method is of course entirely defeated by something that runs git fetch --all, in that case you’d need to either disable it or do something more tedious like:

git fetch # update ‘master’ from remote
git tag base master # mark our base point
git rebase -i master # rewrite some commits
git push --force-with-lease=master:base master:master
I.e. create a base tag for versions of the upstream code that you’ve seen and are willing to overwrite, then rewrite history, and finally force push changes to master if the remote version is still at base, regardless of what your local remotes/origin/master has been updated to in the background.

-f
–force
Usually, the command refuses to update a remote ref that is not an ancestor of the local ref used to overwrite it. Also, when --force-with-lease option is used, the command refuses to update a remote ref whose current value does not match what is expected.

This flag disables these checks, and can cause the remote repository to lose commits; use it with care.

Note that --force applies to all the refs that are pushed, hence using it with push.default set to matching or with multiple push destinations configured with remote.*.push may overwrite refs other than the current branch (including local refs that are strictly behind their remote counterpart). To force a push to only one branch, use a + in front of the refspec to push (e.g git push origin +master to force a push to the master branch). See the … section above for details.

–repo=
This option is equivalent to the argument. If both are specified, the command-line argument takes precedence.

-u
–set-upstream
For every branch that is up to date or successfully pushed, add upstream (tracking) reference, used by argument-less git-pull[1] and other commands. For more information, see branch..merge in git-config[1].

–[no-]thin
These options are passed to git-send-pack[1]. A thin transfer significantly reduces the amount of sent data when the sender and receiver share many of the same objects in common. The default is --thin.

-q
–quiet
Suppress all output, including the listing of updated refs, unless an error occurs. Progress is not reported to the standard error stream.

-v
–verbose
Run verbosely.

–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.

–no-recurse-submodules
–recurse-submodules=check|on-demand|only|no
May be used to make sure all submodule commits used by the revisions to be pushed are available on a remote-tracking branch. If check is used Git will verify that all submodule commits that changed in the revisions to be pushed are available on at least one remote of the submodule. If any commits are missing the push will be aborted and exit with non-zero status. If on-demand is used all submodules that changed in the revisions to be pushed will be pushed. If on-demand was not able to push all necessary revisions it will also be aborted and exit with non-zero status. If only is used all submodules will be recursively pushed while the superproject is left unpushed. A value of no or using --no-recurse-submodules can be used to override the push.recurseSubmodules configuration variable when no submodule recursion is required.

–[no-]verify
Toggle the pre-push hook (see githooks[5]). The default is --verify, giving the hook a chance to prevent the push. With --no-verify, the hook is bypassed completely.

-4
–ipv4
Use IPv4 addresses only, ignoring IPv6 addresses.

-6
–ipv6
Use IPv6 addresses only, ignoring IPv4 addresses.

寫在最後

push本質是將當前分支的頭指針提交到server，順便也修改了本地存儲的server的頭指針（refs/remotes/origin/xx）