Git Cheat Sheet

Git is a distributed version control system.

References

• Github Guide
• Cheat Sheet #1
• Cheat Sheet #2
• Interactive Tutorial

Concepts

Merge

• guide
• combining two branches
• three-way merge
  • common ancestor
  • snapshot to merge into
  • snapshot to merge in
• result of a three-way merge is a merge commit
  • has two parents, one from each branch
• if the branch being merged is directly upstream from the current branch, a “fast-forward” action is take - basically taking the branch pointer and moving ahead. No merge commit is necessary.

Rebase

• alternative to merging
• instead of creating an additional commit for the merge, all the commits in the current branch are re-committed with changes from the master, which makes it look like changes were done from a static version of the master.
• a big trade off is not being able to see when changes were applied
• “golden rule” - never rebase a shared branch

Branch

• A commit is comprised of:
  • commit object - pointer to tree object
  • tree object - links to blob objects
  • blobs - project files
• see this helpful Diagram
• a branch is a movable pointer to a commit
• the default branch name is “master”. Every time a commit is made, this moves forward automatically in fact, every commit made moves some branch forward

Commit

• a commit is made up of
  • commit object - pointer to tree object
  • tree object - links to blob objects
  • blobs - project files
• an object that contains a pointer to the snapshot of the content that was staged,the author and message metadata, and zero or more pointers to the the commit(s) that were the direct parents of this commit.

Snapshot

• state of files at a specific point in time
• Instead of a sequential version number uses codes e.g. 8e1a054 - which is an abbreviation for the full snapshot code
• called a revision in other systems

HEAD

• special pointer to the local branch you are currently working on - to look at a prior state of files, you can move the HEAD pointer to a commit without a branch, but if you are intending to make

Repository

• a location where Git stores the metadata and object database for your project

Working Directory

• single checkout of one version of the project
• files from the compressed database in the Git directory are copied into this folder

Staging Area

• file in your git directory about what will go into the next commit.

Remote

• version of your project that is on a remote server / folder etc

File States in Git

• untracked - file is not in the repository
• unmodified - file is in the repository and identical
• modified - file is in the repository and has been changed
• staged - file is modified and marked as ready for commit

Git Commands

Initialize a new repository

git init

Show current state of repository

git status

Add file(s) to staging

git add file.txt
git add '*.txt'

Add all file(s) to staging

git add -A
git add --all
git add .

Add all updated files to staging

git add -u
git add --update

Restore a directory to last commit

git clean -f  (removes untracked files)
git clean --force
git checkout -f (reverts modified files to previous state)

Commit a set of staged changes to the repository

git commit -m "Commit Message"

Show history of committed changes

git log

Link repository to remote github.com repository

git remote add origin https://github.com/brianvp/myrepo

Push local branch to remote repo

git push -u origin master

Get changes from remote repo

git pull origin master

Show differences between last commit and the remote repo changes pulled in

git diff HEAD
git diff --staged

Unstage files

git reset myfile.txt

Revert files back to last commit

git checkout -- myfile.txt

Make a branch

git branch clean_up

remove old branch

git branch -d clean_up

modify a commit that hasn’t been pushed

git commit --amend

change a modified file back to unmodified

git checkout -- myfile.txt