Set your details

git config --global user.name "John Doe"
git config --global user.email "[email protected]"

Use --global to set the configuration for all projects. If git config is used without --global and run inside a project directory, the settings are set for the specific project.

Make git ignore file modes

cd project/
git config core.filemode false

This option is useful if the file permissions are not important to us, for example when we are on Windows.

See your settings

git config --list

Initialize a git repository for existing code

cd existing-project/
git init

Clone a remote repository

git clone https://github.com/user/repository.git

This creates a new directory with the name of the repository.

Clone a remote repository in the current directory

git clone https://github.com/user/repository.git .

Get help for a specific git command

git help clone

Update and merge your current branch with a remote

cd repository/
git pull origin master

Where origin is the remote repository, and master the remote branch.
If you don't want to merge your changes, use git fetch

View remote urls

git remote -v

Change origin url

git remote set-url origin http//github.com/repo.git

Add remote

git remote add remote-name https://github.com/user/repo.git

See non-staged (non-added) changes to existing files

git diff

Note that this does not track new files.

See staged, non-committed changes

git diff --cached

See differences between local changes and master

git diff origin/master

Note that origin/master is one local branch, a shorthand for refs/remotes/origin/master, which is the full name of the remote-tracking branch.

See differences between two commits

git diff COMMIT1_ID COMMIT2_ID

See the files that changed between two commits

git diff --name-only COMMIT1_ID COMMIT2_ID

See the files changed in a specific commit

git diff-tree --no-commit-id --name-only -r COMMIT_ID

or

git show --pretty="format:" --name-only COMMIT_ID

Source: http://stackoverflow.com/a/424142/1391963

See diff before push

git diff --cached origin/master

See diff with only the changed lines (no context)

git diff --unified=0

See details (log message, text diff) of a commit

git show COMMIT_ID

Count the number of commits

git rev-list HEAD --count

git rev-list COMMIT_ID --count

Check the status of the working tree (current branch, changed files...)

git status

Make some changes, commit them

git add changed_file.txt
git add folder-with-changed-files/
git commit -m "Committing changes"

Rename/move and remove files

git rm removeme.txt tmp/crap.txt
git mv file_oldname.txt file_newname.txt
git commit -m "deleting 2 files, renaming 1"

Change message of the last commit

git commit --amend -m "New commit message"

Push local commits to remote branch

git push origin master

Push commits to all remotes, in a single command

Git does not do that, but see https://stackoverflow.com/a/18674313/1391963

See recent commit history

git log

See commit history for the last two commits

git log -2

See commit history for the last two commits, with diff

git log -p -2

See commit history printed in single lines

git log --pretty=oneline

Revert one commit, push it

git revert dd61ab21
git push origin master

Revert to the moment before one commit

# reset the index to the desired tree
git reset 56e05fced

# move the branch pointer back to the previous HEAD
git reset --soft HEAD@{1}

git commit -m "Revert to 56e05fced"

# Update working copy to reflect the new commit
git reset --hard

Source: http://stackoverflow.com/q/1895059/1391963

Undo the last commit, preserving local changes

git reset --soft HEAD~1

Undo the last commit, without preserving local changes

git reset --hard HEAD~1

Undo the last commit, preserving local changes in the index

git reset --mixed HEAD~1

Or git reset HEAD~1
See also http://stackoverflow.com/q/927358/1391963

Undo non-pushed commits

git reset origin/master

Reset to remote state

git fetch origin
git reset --hard origin/master

See local branches

git branch

See all branches

git branch -a

Make some changes, create a patch

git diff > patch-issue-1.patch

Add a file and create a patch

git add newfile
git diff --staged > patch-issue-2.patch

Add a file, make some changes, and create a patch

git add newfile
git diff HEAD > patch-issue-2.patch

Make a patch for a commit

git format-patch COMMIT_ID

Make patches for the last two commits

git format-patch HEAD~2

Make patches for all non-pushed commits

git format-patch origin/master

Create patches that contain binary content

git format-patch --binary --full-index origin/master

Apply a patch

git apply -v patch-name.patch

Apply a patch created using format-patch

git am patch1.patch

Break up multiple changes into separate commits (or commit only part of a changed file)

git add --patch file.txt
(press 'y' for the chunks to add)
git commit -m 'first part of the file'
(repeat if desired)

Sources: https://stackoverflow.com/q/4948494/1391963, https://stackoverflow.com/q/1085162/1391963

Create a tag

git tag 7.x-1.3

Push a tag

git push origin 7.x-1.3

Create a branch

git checkout master
git branch new-branch-name

Here master is the starting point for the new branch. Note that with these 2 commands we don't move to the new branch, as we are still in master and we would need to run git checkout new-branch-name. The same can be achieved using one single command: git checkout -b new-branch-name

Create a branch from a previous commit

git branch branchname sha1-of-commit

or using a symbolic reference (e.g. last commit):

git branch branchname HEAD~1

You can also use

git checkout -b branchname sha1-of-commit

Source: http://stackoverflow.com/a/2816728/1391963

Check out a branch

git checkout new-branch-name

See commit history for just the current branch

git cherry -v master

(master is the branch you want to compare)

Merge branch commits

git checkout master
git merge branch-name

Here we are merging all commits of branch-name to master.

Merge a branch without committing

git merge branch-name --no-commit --no-ff

See differences between the current state and a branch

git diff branch-name

See differences in a file, between the current state and a branch

git diff branch-name path/to/file

Delete a branch

git branch -d new-branch-name

Push the new branch

git push origin new-branch-name

Get all branches

git fetch origin

Get the git root directory

git rev-parse --show-toplevel

Source: http://stackoverflow.com/q/957928/1391963

Remove from repository all locally deleted files

git rm $(git ls-files --deleted)

Source: http://stackoverflow.com/a/5147119/1391963

Delete all untracked files

git clean -f

Including directories:

git clean -f -d

Preventing sudden cardiac arrest:

git clean -n -f -d

Source: http://stackoverflow.com/q/61212/1391963

Delete all files from a git repository that have already been deleted from disk:

git ls-files --deleted -z | xargs -0 git rm

Source (and alternatives): https://stackoverflow.com/a/5147119/1391963

Show total file size difference between two commits

Short answer: Git does not do that.
Long answer: See http://stackoverflow.com/a/10847242/1391963

Unstage (undo add) files:

git reset HEAD file.txt

See closest tag

git describe --tags `git rev-list --tags --max-count=1`

Source: http://stackoverflow.com/q/1404796/1391963. See also git-describe.

Debug SSH connection issues

GIT_SSH_COMMAND="ssh -vvv" git clone <your_repository>

Have git pull running every X seconds, with GNU Screen

screen
for((i=1;i<=10000;i+=1)); do sleep 30 && git pull; done

Use Ctrl+a Ctrl+d to detach the screen.

See previous git commands executed

history | grep git

or

grep '^git'  /root/.bash_history

See recently used branches (i.e. branches ordered by most recent commit)

git for-each-ref --sort=-committerdate refs/heads/ | head

Source: http://stackoverflow.com/q/5188320/1391963

Create a tar.xz file with all project files (excluding .git directory)

git archive --format tar HEAD | xz > project.tar.xz

Git built-in alternative to the previous command

cd ..
tar cJf project.tar.xz project/ --exclude-vcs

Create a tar with locally modified files

git diff --name-only | xargs tar -cf project.tar -T -

Look for conflicts in your current files

grep -H -r "<<<" *
grep -H -r ">>>" *
grep -H -r '^=======$' *

There's also git-grep.

Apply a patch not using git:

patch -p1 < file.patch