git init                               # initialize a Git repo in the current directory
git clone https://github.com/code.git  # clone the code.git repository together with history

git add <filename>                     # add a single file to staging
git add -u                             # add all updated or deleted files to staging (not untracked new files)
git add -A                             # add all files including untracked ones

git commit -m "comment"                # commit all staged files
git commit --amend --no-edit           # add more changes to your last commit

git mergetool                          # use a merge tool to resolve merge conflicts

git diff efd22..611ce                  # show differences between the commit efd22 (older) and 611ce (newer)
git diff HEAD~1..HEAD                  # show diff between one commit back (HEAD~1) and the latest commit (HEAD)
git diff HEAD~1..                      # the same as above; HEAD is assumed by default
git diff --cached                      # compare the repository to the staging area

git checkout <filename>                # checkout a file from the repository to revert changes in your working
                                       # directory
git reset --hard                       # remove all the current changes - modifications and deletions
git reset --soft HEAD~1                # move all the changes from the last commit back to staging
git reset --hard HEAD~1                # remove the last commit and discard all the changes
git clean -n                           # list files that would be removed by 'git clean' (untracked files)
git clean -f                           # remove the files

git log                                # list the commits together with their SHA1 in the chronological order
git log --oneline                      # list commits, one per line
git log --oneline | wc -l              # count the number of commits in the repo
git log --oneline --graph              # show the commit history on the current branch as a graph
                                       # with branches and merges
git log --oneline --graph --all        # show the commit history on all branches
git log --oneline --graph --all --decorate # additionally apply labels to the commits such as tags, local branches
                                       # and remote branches
git log --format=short                 # list commits showing only the author and the commit message
git log <branch_name>                  # list commits from the given branch
git log origin/master                  # example: branch_name is 'origin/master'
git shortlog                           # list commit messages by authors and the number of commits
git shortlog -sne                      # list commit messages and include: s - summary, n - order by the number
                                       # of commits decreasing, e - include the user's email
git show HEAD                          # show the last commit
git show HEAD~1                        # show the commit before the last one
git show <SHA1>                        # show the commit with the given SHA1
 
git reflog                             # show the history of where HEAD pointed

git --version
git status                             # show status and untracked files
git status --short                     # show short status: M - modified, A - new, ? - untracked
                                       # col1: staged, col2: modified
git status -s                          # the same as show short status
git tag                                # list versions that have been tagged

git fetch                              # pull out changes from a remote repo
git fetch <remote_name>                # specify a remote to fetch from (if you have multiple remotes)
 
git merge <branch_name>                # merge from the branch branch_name to the current branch
git merge feature1                     # example: merge 'feature1' branch to the current branch
                                       # HEAD, master, feature1 are all together
                                       # it's save to delete the feature1 branch because it's been merged
 
git pull                               # = git fetch; git merge origin/master

git stash
git stash list
git stash apply
git stash pop
git stash drop
git stash branch <branch_name>         # create a new branch and apply the stash to it

# Add a remote repo and name it 'origin'. It does not have to be called 'origin'. You can call it any name.
> git remote add origin https://github.com/wbs/TestRepo.git
> git remote                           # show the remote repos
origin                                 # 'origin' is the remote the source code came from
> git remote -v                        # show remote repos with URLs
origin  https://github.com/wbs/TestRepo.git (fetch)
origin  https://github.com/wbs/TestRepo.git (push)
> git remote rm origin                 # remove the remote 'origin'

# Extablish a correspondence between your local branch and a remote branch.
# Cloning sets the upstream branches automatically.
# git branch --set-upstream-to <local_branch> <remote_branch>
 
> git branch --set-upstream-to master origin/master
Branch master set up to track remote branch master from origin.
 
> git pull                             # pull the updates from origin/master
 
# You can also specify the upstream branch explicitly
> git pull origin origin/master
 
# Push the current branch and set the remote as upstream
> git push --set-upstream origin origin/master

Branches are labels on SHA1 hashes of individual commits.

git branch                             # show local branches
git branch -r                          # show remote branches
git branch -a                          # show all (local and remote) branches
git branch -a | grep integ             # show branches which the name that contains 'integ'
git branch -m <old_name> <new_name>    # rename (move) a branch
git branch -d <branch_name>            # delete a branch; if there are any not merged commits the branch
                                       # won't be deleted; it's safe to delete a branch after it's been merged
git branch -D <branch_name>            # force deletion of a branch with all the commits
git branch <branch_name> <commit_SHA1> # recover a commit

git checkout <branch_name>             # checkout an existing branch
git checkout -b <branch_name>          # create a new branch and check it out

Example: Create a new branch and switch to it:

ltara@WBS MINGW64 /c/Projects/Test (origin/master)
$ git branch feature1
 
ltara@WBS MINGW64 /c/Projects/Test (origin/master)
$ git checkout feature1
Switched to branch 'feature1'
 
ltara@WBS MINGW64 /c/Projects/Test (feature1)
$ git log --graph --oneline --all --decorate
* 77f6a47 (HEAD -> feature1, origin/master, master) Change README
* dded7b8 Fix typo in README.txt
...

Example cont'd: Modify a file and create a commit:

ltara@WBS MINGW64 /c/Projects/Test (feature1)
$ echo "Feature1" >> README.txt
 
ltara@WBS MINGW64 /c/Projects/Test (feature1)
$ git commit -am "Add feature1"
[feature1 b7ef1be] Add feature1
 1 file changed, 1 insertion(+)
 
ltara@WBS MINGW64 /c/Projects/Test (feature1)
$ git log --graph --oneline --all --decorate
* b7ef1be (HEAD -> feature1) Add feature1
* 77f6a47 (origin/master, master) Change README
* dded7b8 Fix typo in README.txt
...

Example cont'd: Switch back to master:

ltara@WBS MINGW64 /c/Projects/Test (feature1)
$ git checkout master
Switched to branch 'master'
 
ltara@WBS MINGW64 /c/Projects/Test (master)
$ git log --graph --oneline --all --decorate
* b7ef1be (feature1) Add feature1
* 77f6a47 (HEAD -> master, origin/master) Change README
* dded7b8 Fix typo in README.txt
...

Example cont'd: Create another branch (feature2) and check it out:

ltara@WBS MINGW64 /c/Projects/Test (master)
$ git checkout -b feature2
Switched to a new branch 'feature2'
 
ltara@WBS MINGW64 /c/Projects/Test (feature2)
$ git log --graph --oneline --all --decorate
* b7ef1be (feature1) Add feature1
* 77f6a47 (HEAD -> feature2, origin/master, master) Change README
* dded7b8 Fix typo in README.txt
...

Example cont'd: Modify the same file as in feature1 and create a commit:

ltara@WBS MINGW64 /c/Projects/Test (feature2)
$ echo "Feature2" >> README.txt
 
ltara@WBS MINGW64 /c/Projects/Test (feature2)
$ git commit -am "Add feature2"
[feature2 eca0562] Add feature2
 1 file changed, 1 insertion(+)
 
ltara@WBS MINGW64 /c/Projects/Test (feature2)
$ git log --graph --oneline --all --decorate
* eca0562 (HEAD -> feature2) Add feature2
| * b7ef1be (feature1) Add feature1
|/
* 77f6a47 (origin/master, master) Change README
* dded7b8 Fix typo in README.txt
...

System-level configuration applies to the entire computer Git is installed on.

• Linux: /etc/gitconfig
• Windows: C:\Program Files\Git\mingw64\etc

User-level configuration:

• Linux: ~/.gitconfig
• Windows: C:\Users\USERNAME\.gitconfig -or- C:\Users\USERNAME\.gitconfig.d

Repository-level configuration

• Stored in .git/config in each repo

git config --system [action]   # access system config file (system-level)
git config --global [action]   # access global config file (user-level)
git config --local [action]    # access repository config file (repo-level)
 
git config --local --list      # list the repo-level configuration
 
# remove a setting, for example help.autocorrect
git config --global --unset help.autocorrect

git config --global user.name "Mike McFerry"
git config --global user.email "mferry@email.com"
 
# for editing commit messages and viewing diffs
git config --global core.editor notepad 
 
# enable autocorrecting misspelled git commands, for example 'git statsu' --> 'git status'
git config --global help.autocorrect 1
 
# use colors when showing information (only in terminal)
git config --global color.ui auto

git config --global core.autocrlf true   # convert crlf to lf before storing in repo and then back to crlf when
                                         # pulling from repo; good for Windows development
 
git config --global core.autocrlf input  # convert crlf to lf before storing in repo but don't do anything when
                                         # pulling from repo; good for Linux and Mac
 
git config --global core.autocrlf false  # do not convert crlf; Windows development only

Example: Define an alias:

> git config --global alias.lga "log --oneline --graph --all --decorate"
 
> git lga
* 77f6a47 (HEAD -> origin/master, master) Latest changes to README
* dded7b8 Fixed typo in README.txt
* 977c77f Fixed bug#123
* 48bcb3c Added cool new feature
* 611ce6b Another update
* efd22b4 Added README.txt
 
> cat ~/.gitconfig
[alias]
        lga = log --oneline --graph --all --decorate

VCS stands for Version Control System

Types of VCS:

• Local VCS: The version db is stored locally on your computer. Each change is stored as a version patch in the db.
• Centralized VCS: The version db is located on a central server. Collaborators have a snapshot of a single file they are currently working on.
• Distributed VCS: The version db resides on each contributor's computer i.e., each client has a full backup of the entire project.

Git checksums:

• Each version of a file in Git has a unique 40-chars long checksum.
• If the checksum is the same, the files must be the same.
• The checksums are generated by SHA1 hashing algorithm.

The three stages of a tracked file in Git:

• Committed (stored in the local Git database)
• Modified (work in progress)
• Staged (marked for commit)

The three states of a Git project:

• Working Directory (Updated) - This is a copy of a single version of the project from Origin. It contains updated files that have not been added to the staging area yet.
• Staging Area (Index) - It contains one or more updated files staged for the next commit.
• .git Repository (Origin) - These are the files cloned from a remote server and stored locally as the Git database and metadata. It contains committed files.

How to Write a Git Commit Message