add post 03-17

_posts/2014/2014-03-17-Git_merge_--squash_and_git_rebase.md

@@ -0,0 +1,53 @@
+---
+layout: post-en
+title: Git Cookbook
+categories:
+- Common Tec
+tags:
+- Git
+---
+
+> One advantage for Git comes from its powerful branch management capability, but it will be hard to maintain the commit history between different branch. As Linus said that [Clear and Clean is important for the commit history](http://blog.sevenche.com/2014/02/Linus-Torvalds-rules-for-using-Git/). Here in this article I am going to demonstrate how `git merge --squash`, `git merge`, and `git rebase` will affect the commit history.
+
+### `git merge` and `git merge --squash`
+
+In below example I am going to merge `dev3` into `dev2` and `dev4` by using merge with and without `--squash` parameter. 
+Initial status:
+![](/media/pic2014/0317-2.png)
+
+**merge with `--squash` test**
+```
+git checkout dev4
+git merge --squash dev3
+git commit -a
+```
+We can see changed files in working directory and after commit we don't see `fbcb87a` and `b85fcb7` in the history of `dev4`
+
+**Plain merge **
+
+```
+git checkout dev2
+git merge dev3
+```
+![](/media/pic2014/0317-3.png)
+Now `dev4` and `dev2` have the same content, but we cannot see `dev4` comes contains commit form `dev3`, but `dev2` has the information. 
+
+** Conclusion **
+`--squash` will abandon the merge history, so you will not know what was merged. Only use it when you don't want these commit history!
+
+### Rebase
+
+** Before rebase **
+![](/media/pic2014/0317-0.png)
+
+** rebase **
+```
+git checkout dev
+git rebase master
+```
+** After rebase **
+> Notice: dev commit ccd4673 changed to 9d76e0b
+![](/media/pic2014/0317-1.png)
+
+** Conclusion**
+Rebase do not like merge - which will cause a commit, and from the tree you cannot see when the dev is split out and when it is merged back. - So Linus calls it is a _clean_ for history.