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Git is an open-source version control system. It is used to manage a set of files, as they change over time.


  • Working Directory: simply the files in the root folder
  • Commit: A certain version of the files
  • Tag: a named pointer to a certain commit.
  • Branch: A chain of commits
  • Master: Default Branch
  • Head: a named pointer to the current branch

Repository: It is stored in the same directory as the project itself, in a subdirectory called .git.

Commit Object#

A Commit Object is a set files. It can be referred by its partial or full SHA1 name or relative to a head. The postfix ^ refers to the parent of a head.

Head: simply a named reference to a commit object. By default, there is a head in every repository called master.



The index (= Stage = Cache)


Tags are pointers to a certain commit. They use a name which is more memorizeable than the hash of the commit.

Creating and Cloning#

There are two ways to create a repository:

  1. Online: You create the repository on the website (e.g. and afterwads clone the empty repository with git clone git://...
  2. Offline: You create a new repository in the current directory with git init

Diagnose and Information#

git status lists modified and untracked files
git diff HEAD shows changes between working dir and HEAD

Commiting Changes#

Merge master into feature branch#

git fetch origin master:master
git rebase master
git push -f
  • view file, click on start line number
  • hold shift, click on end line
  • press y to create permanent URL (hash)

Repairing and Restoring#

Undo changes#

  • Local changes: To undo local changes use git checkout -- <FILE>. If <FILE> is already staged (happens if you do git add), you can use git reset HEAD <FILE> and then git checkout -- <FILE>
  • Commit staging: If you want to undo the commit command meaning you move changes back to staging (still there but uncommited), use git reset --soft HEAD^.
  • Committed changes: If you already commited changes but you want to reset all changes to the version of the origin, you can use git reset --hard origin/master

Recover deleted files#

  • Local deletes: You can view delted files with git ls-files --deleted. Afterwards you can recover delted files with git checkout -- <FILE>
  • Committed deletes: If the deletion has been committed, find the commit where it happened, then recover the file from this commit.
git rev-list -n 1 HEAD -- <file>
git checkout <commit>^ -- <file>

Testing and Merging Pull Requests#

To checkout a pull request (e.g. #37) locally for testing it, run

git fetch origin pull/37/head:pr37
git checkout pr37