Git Learning Notes

本地操作

初始配置用户信息
```
$ git config --global user.name "Your Name"
$ git config --global user.email "email@example.com"
```
–global will apply the name and email configuration to all repositories on your device.

创建一个仓库

$ mkdir learngit
$ cd learngit
$ pwd
/Users/Xiaocheng/learngit
$ git init
Initialized empty Git repository in /Users/Xiaocheng/learngit/.git/

First commit

Create a new file “readme.txt” under learngit directory, then enter

$ git add readme.txt
$ git commit -m "wrote a readme file"
[master (root-commit) eaadf4e] wrote a readme file
1 file changed, 2 insertions(+)
create mode 100644 readme.txt

Can commit several files at a time.

add之后可以查看修改的内容

Use git status to check modifying status. Use git diff readmen.txt to check modified contents.
Version Backoff

Check commit log using git log or
```
$ git log --pretty=oneline
```
HEAD represents current version, HEAD^ the previous, HEAD^^ the second previous, HEAD~100. Directly use HEAD to backoff:
```
$ git reset --hard HEAD^
HEAD is now at e475afc add distributed
```
Or use version number:
```
$ git reset --hard 1094a
HEAD is now at 83b0afe append GPL
```
Use git reflog to see version-changing records.
Working Directory and Repository, stage.

See 廖雪峰的git教程
Managing Modification

Use git diff HEAD -- readme.txt to show difference between working directory and repository.
撤销修改

Modified in working directory
```
$ git checkout -- <file>
```
Modification already added into state
```
$ git reset HEAD <file>
```
then the modification back to working directory. If modification already committed, use version backoff to undo it.
Delete a file

After deleting a file in working directory, we can see the differences using git status. Confirm this operation,
```
$ git rm test.txt
rm 'test.txt'

$ git commit -m "remove test.txt"
[master d46f35e] remove test.txt
 1 file changed, 1 deletion(-)
 delete mode 100644 test.txt
```
Before committing, can recover it.
```
$ git checkout -- <file>
```
Connect to Github

Need to create SSH Key for the beginner.
```
$ ssh-keygen -t rsa -C "youremail@example.com"
```
Don’t forget you password!

And paste id_rsa.pub into “Account settings/Add SSH key” on github.

First push

If you already have an empty repository in github say learngit,

$ git remote add origin git@github.com:currybur/learngit.git

“origin” is the name of remote repository, can be replaced, but usually not. Then push native repository to remote.

$ git push -u origin master
Counting objects: 20, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (15/15), done.
Writing objects: 100% (20/20), 1.64 KiB | 560.00 KiB/s, done.
Total 20 (delta 5), reused 0 (delta 0)
remote: Resolving deltas: 100% (5/5), done.
To github.com:michaelliao/learngit.git
* [new branch]      master -> master
Branch 'master' set up to track remote branch 'master' from 'origin'.

We use -u param for the first pushing of master branch, which associates native master branch with remote master branch.

First Clone

Have a non-empty repository,

$ git clone git@github.com:currybur/learngit.git
Cloning into 'gitskills'...
remote: Counting objects: 3, done.
remote: Total 3 (delta 0), reused 0 (delta 0), pack-reused 3
Receiving objects: 100% (3/3), done.

Then a learngit directory is created. Note that we can also use https, which is slower and needs passwords each time connecting.

Branches Management

Create a new branch.
```
$ git checkout -b dev
Switched to a new branch 'dev'
```
which is equal to
```
$ git branch dev
$ git checkout dev
Switched to branch 'dev'
```
Check the current branch.
```
$ git branch
* dev
  master
```
After finishing the work on dev branch, we can go back to master branch and merge the result.
```
$ git merge dev
Updating d46f35e..b17d20e
Fast-forward
readme.txt | 1 +
1 file changed, 1 insertion(+)
```
Then delete dev branch. $ git branch -d dev Deleted branch dev (was b17d20e). We can also use switch command instead of checkout. For example, create and switch to a new branch
```
$ git switch -c dev
```
Just want to switch to a currently existing branch
```
$ git switch master
```

Dealing with Conflict

After modifying on different branches respectively, we can not directly merge them. Can go to the file where the conflict occurs, and fix it. Use git log to check branches’ merging information.

$ git log --graph --pretty=oneline --abbrev-commit
*   cf810e4 (HEAD -> master) conflict fixed
|\  
| * 14096d0 (feature1) AND simple
* | 5dc6824 & simple
|/  
* b17d20e branch test
* d46f35e (origin/master) remove test.txt
* b84166e add test.txt
* 519219b git tracks changes
* e43a48b understand how stage works
* 1094adb append GPL
* e475afc add distributed
* eaadf4e wrote a readme file

Branch Managing Policy

git merge will be executed in Fast forward mode, which throws the information of branching away. We can use the git merge --no-ff parameter.

Storing Working Scene on a Branch

If we have work unfinished on dev branch, and have to do another task

$ git status
On branch dev
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

  new file:   hello.py

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

  modified:   readme.txt

Then use git stash to store them. After another task, to ressume the stored work, first check

$ git stash list
stash@{0}: WIP on dev: f52c633 add merge

Here we have git stash apply to recover and not delete it from stash, git stash drop is needed. Or use git stash pop. Can stash particular task.

$ git stash apply stash@{0}

Copy Modification Commit to Other Branches

After committing on master branch, we want to repeat on dev branch.

$ git branch
* dev
  master
$ git cherry-pick 4c805e2
[master 1d4b803] fix bug 101
1 file changed, 1 insertion(+), 1 deletion(-)

Developing a New Feature

Should better create a new feature branch. If we want to abandon it before merging,
```
$ git branch -D feature-vulcan
Deleted branch feature-vulcan (was 287773e).
```
Cooperation

Try to push my modification
```
$ git push origin <branch-name>
```
Failed for the remote being newer than my local, so try to merge
```
$ git pull
```
If there are conflicts, solve it and commit locally, then
```
$ git push origin <branch-name>
```

一些tips

报错fatal: refusing to merge unrelated histories，如果合并了提交历史不同的仓库，为了防止程序员手残，git就会给这么个提示。确认后使用 --allow-unrelated-histories来完成merge。

有时候发现commit没记录了，可能是提交的用户邮箱和github上留的不一样，git config user.name/user.email查看，不对就

$ git config --global user.??? "your name/email"

也可以把之前错误的提交记录全改了，首先新clone一份仓库

$ git clone --bare your-repo
$ cd your-repo.git

然后粘贴这个脚本

  #!/bin/sh
  git filter-branch --env-filter '
  OLD_EMAIL="旧的Email地址"
  CORRECT_NAME="正确的用户名"
  CORRECT_EMAIL="正确的邮件地址"
  if [ "$GIT_COMMITTER_EMAIL" = "$OLD_EMAIL" ]
  then
      export GIT_COMMITTER_NAME="$CORRECT_NAME"
      export GIT_COMMITTER_EMAIL="$CORRECT_EMAIL"
  fi
  if [ "$GIT_AUTHOR_EMAIL" = "$OLD_EMAIL" ]
  then
      export GIT_AUTHOR_NAME="$CORRECT_NAME"
      export GIT_AUTHOR_EMAIL="$CORRECT_EMAIL"
  fi
  ' --tag-name-filter cat -- --branches --tags

回车，就把这个clone里的提交历史改了，然后push

$ git push --force --tags origin 'refs/heads/*'

卸磨杀驴删掉这个clone

$ cd ..
$ rm -rf repo.git

本地操作

Connect to Github

一些tips