The difference between 'git fetch' and 'git pull'

Both git fetch and git pull can update the remote repository to the local one. So what are the differences between them? There are several concepts that have to be mentioned to clarify this issue.

FETCH_HEAD: is a version link, recorded in a local file, pointing to the end version of the branch that has been taken down from the remote warehouse.

commit-id: After each local work is completed, a git commit operation will be performed to save the current work to the local repo, and a commit-id will be generated at this time , which is a serial number that uniquely identifies a version. After using git push, this serial number will also be synchronized to the remote warehouse.

With the above concepts, let’s talk about git fetch

git fetch: This will update the latest commit-id of the branches contained in all remote warehouses in git remote. Record it into the .git/FETCH_HEAD file
The way git fetch updates the remote warehouse is as follows:

git fetch origin master:tmp 
//在本地新建一个temp分支，并将远程origin仓库的master分支代码下载到本地temp分支
git diff tmp 
//来比较本地代码与刚刚从远程下载下来的代码的区别
git merge tmp
//合并temp分支到本地的master分支
git branch -d temp
//如果不想保留temp分支 可以用这步删除

(1) If you use git fetch directly, the steps are as follows:

• Create and update local remote branches. That is, create and update the origin/xxx branch, and pull the code to the origin/xxx branch.

• Set the current branch-origin/current branch correspondence in FETCH_HEAD. If you directly git merge at that time, origin/abc can be merged into the abc branch.

(2) git fetch origin
Just manually specify the remote to fetch. When no branch is specified, it usually defaults to master

(3) git fetch origin dev
Specify remote remote and FETCH_HEAD, and only pull the commits of this branch.

This command will access the remote warehouse and pull all the data you don't have yet. Once the execution is complete, you will have references to all branches in that remote repository, which can be merged or viewed at any time.

If you use the git clone command to clone a warehouse, the command will automatically add it as a remote warehouse (git remote -v) and use "origin" as the abbreviation by default. So, git fetch origin will fetch all work newly pushed since the clone (or last fetch). It's important to note that the git fetch command will pull data into your local repository - it will not automatically merge or modify your current work. You must manually incorporate it into your job when ready.

If you have a branch set up to track a remote branch, you can use the git pull command to automatically fetch and merge the remote branch into the current branch. This may be an easier or more comfortable workflow for you; by default, the git clone command automatically sets the local master branch to track the cloned remote repository's master branch (or whatever the default branch is called). Running git pull will usually grab the data from the originally cloned server and automatically try to merge into the current branch.

git pull: First, based on the local FETCH_HEAD record, compare the local FETCH_HEAD record with the version number of the remote warehouse, and then git fetch obtains the subsequent version data of the remote branch currently pointed to. , and then use git merge to merge it with the local current branch. So it can be considered that git pull is a combination of the two steps of git fetch and git merge.

The usage of git pull is as follows:

git pull <远程主机名> <远程分支名>:<本地分支名>
//取回远程主机某个分支的更新，再与本地的指定分支合并。

Therefore, compared with git pull, git fetch is equivalent to getting the latest version from the remote to the local, but it will not automatically merge. If you need to selectively merge git fetch is a better choice. When the effect is the same, git pull will be faster.

Note: Using git pull to update the code is relatively simple and violent. However, based on the commit ID, their actual implementation principles are different, so don’t use git pull. Use git fetch and git merge to make it easier. Safety.

Recommended tutorial: "Git"

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