Notes of Git

written on December 30, 2012

Pro Git is an excellent book about Git, and these are my reading notes.

This is a brief notes about some points of Pro Git. It only contains first 3 chapters (contains most commonly used commands of Git). I will maintain this article and keep revising it. Hope it might helpful to you.

##Before Running Git

• Snapshots, Not Differences
  The major difference between Git and any other VCS (Subversion and friends included) is the way Git thinks about its data. Conceptually, most other systems store information as a list of file-based changes.

• Nearly Every Operation Is Local
  Most operations in Git only need local files and resources to operate ¡ª generally no information is needed from another computer on your network.

• Git Has Integrity
  Git use checksum, namely, SHA-1, as a reference.

• Three States Git has three main states that your files can reside in: committed, modified, and staged. Committed means that the data is safely stored in your local database. Modified means that you have changed the file but have not committed it to your database yet. Staged means that you have marked a modified file in its current version to go into your next commit snapshot.

  The basic Git workflow goes something like this:

  1. You modify files in your working directory.
  2. You stage the files, adding snapshots of them to your staging area.
  3. You do a commit, which takes the files as they are in the staging area and stores that snapshot permanently to your Git directory.

##Git Basics

• Clone
  git clone git://github.com/USERNAME/REPO.git

• Check Status git status

• Trace New File
  git add FILE (The FILE edited after git add need to redo git add to store the changes)

• Gitignore
  if you want to ignore some files, add thier patter to .gitignore. Like *.[oa] (generate while compiling)

Glob patterns are like simplified regular expressions that shells use. An asterisk (*) matches zero or more characters; [abc]matches any character inside the brackets (in this case a, b, or c); a question mark (?) matches a single character; and brackets enclosing characters separated by a hyphen([0-9]) matches any character between them (in this case 0 through 9) .

• Diff between staged and last commit file
  git diff --cached

• Committing Changes
  git status before git commit. add -m flag to add commit message, -v to explicit remind every place you modified, -a to automatically stage every file that is already tracked before doing the commit, letting skip the git add part.

• Remove
  rm FILE and git rm FILE to delete local files. git rm --cached FILE to remove files in repository.(Could use glob)

• Move
  git mv OLD NEW to change the names.

• Viewing History
  git log, add -p to show differences in every commits, use -2 to see lasted 2 updates, –stat abbreviated stats, –pretty customized formats.

• Undo
  use git commit --amend to add forgetted files or reedit commit messages. (See Book 2.4.1)

• Unstaging Staged File
  git reset HEAD FILE

• Unmodifying a Modified File
  use git status (See Book 2.4.3)

• Fetching and Pulling
  git fetch REMOTE-NAME pull down all the data from that remote project that you don’t have yet.

git fetch origin fetches any new work that has been pushed to that server since you cloned (or last fetched from) it. It’s important to note that the fetch command pulls the data to your local repository and it doesn’t automatically merge it with any of your work or modify what you’re currently working on. You have to merge it manually into your work when you’re ready.

• Push
  git push origin master will push local master branch to origin server.

• Tagging
  git tag to add tags.-a to annotated, -m add comments, git show to check version info.

• Git Aliases
  You can set up an alias for each command with git config. For example, using git config --global alias.ci commit to instead git commit with git ci. Useful Tips: git config --global alias.last 'log -1 HEAD' to check last commit by git last.

Git Branches

• HEAD
  In Git, this is apointer to the local branch you’re currently on.

• New Branch
  Because a branch in Git is in actuality a simple file that contains the 40 character SHA-1 checksum of the commit it points to, branches are cheap to create and destroy. Creating a new branch is as quick and simple as writing 41 bytes to a file (40 characters and a newline).

• Basic Branching and Merging
  switch to a certain branch git Check -b BRANCH-B, git merge to merge to master.

• Delete Branch
  git branch -d to delete branches. It could be failed if it was unmerged. Thus, you could use git branch -D BRANCH-B to force deleting it, and git branch --no-merged to check unmerged work.

• Remote Branch
  You’d better read the related part of this book! It is a little comfusing but important.

• Rebasing
  With the rebase command, you can take all the changes that were committed on one branch and replay them on another one. For example, git rebase master server checks out the topic branch (in this case,server) for you and replays it onto the base branch (master).It quite cool, read Book 3.5.1 to know more. Summed up in one line Do not rebase commits that you have pushed to a public repository.