Git Primer for Busy People

2016-12-05 ·
This is work-in-progress, suggestions or tips are welcome. To move around efficiently, use `Ctrl-F`. Last updated: Dec 30th, 2017

Git (current version 2.15.1) is an open source distributed version control system. It has a tiny footprint with lightning fast performance.

Architecture

Storage

Git uses files for storage. A commit is a file with the commit message, associated data (name, email, date/time, previous commit, etc) and with a link to a tree file. The tree file contains a list of objects or other trees. The object or blob is the actual content associated with the commit (the filename isn’t stored in the object, but in the tree). Files are stored with a filename of a SHA-1 hash of the object.

Branches and tags are files containing SHA-1 hashes pointing to particular commits. Creating a new branch means creating a file with the name of the branch and the SHA-1 reference to the current commit. Current branch is marked as HEAD. All the branch pointers are kept in .git/refs/heads, HEAD is stored in .git/HEAD file and tags are stored in .git/refs/tags. Additionally, ORIG_HEAD backs up the position of HEAD before a potentially dangerous operation

Modes

« Changes are staged » means they are added to the index. « Changes are unstaged » means they are not added to the index but present in the working directory. Commits are only made from staged changes.

Staging area is a place to short list changes to be added with the next commit; also known as index, cache, staged files area or just stage.

Relative commit markers (i.e. ^ & ~)

Carats ^ and tildes ~ are relative commit markers in Git. HEAD^1 (or HEAD^) means « 1st parent of HEAD ». HEAD^2 means « 2nd parent of HEAD » (present if there's been a merge). HEAD^^ is not the same as HEAD^2. HEAD^^ means « the 1st parent of the 1st first parent ». HEAD^^ equals to HEAD~2

Also:

HEAD^1 == HEAD^ == HEAD~1 == HEAD~
HEAD^^ == HEAD~2

Configuration

List configuration settings

git config --list

Set user name and email

git config --global user.name "John Appleseed"
git config --global user.email "john@apple.com"

Create alias

git config --global alias.lr 'log --reverse'

Set up pager to wrap lines

git config core.pager 'less -r'

Repository

Unstage all staged files

git reset

Remove untracked files from the repository

git clean -f

Show untracked files to be removed from the repository

git clean -f -n

-n equals to --dry-run

Remove untracked files & directories from the repository

git clean -fd

Remove (interactively) untracked files & directories from the repository

git clean -i

Remove file from source control but not from the project

git rm --cached config/database.yml

Commit

Add empty commit

git commit -m 'Here goes commit message' --allow-empty

Unstage file

git reset HEAD <file name>

Undo last commit & keep changes (if local)

git reset HEAD~

Undo last commit & keep changes in index (if local)

git reset --soft HEAD~

Undo last commit & destory changes (if local)

git reset --hard HEAD~

Undo last commit (if pushed)

git revert HEAD

Undo single file from last commit (if local)

git reset HEAD~ file.txt
git commit --amend --no-edit

or

git reset --soft HEAD~
git reset HEAD file.txt # good changes are staged, ready to be committed
git commit

Squash last 3 commits

git reset --soft HEAD~3
git commit

(only if the the oldest one is not the initial commit)

Squash into the initial commit

git rebase -i --root master

Squash any 3 commits

Let's assume B is the SHA of the commit to squash in.

git rebase -i B

and then

pick B ...
squash C ...
squash D ...
...

Apply patch

curl https://github.com/zaiste/kulfon/pull/42.patch > /tmp/42.patch
git apply --check /tmp/42.patch
git apply /tmp/42.patch

Find lost commits using reflog

git log -g

Find lost commits using fsck

git fsck --full

Merge

Undo merge with conflicts

git merge --abort

It resets the working directory to whatever state it was in before the merge. It should restore any uncommitted changes from before the merge.

Older syntax (Git < 1.7.4) which does the same as the above:

git reset --merge

In Git < 1.6.2 you have to use

git reset --hard

which removes all uncommitted changes, including the uncommitted merge.

Branch

Create branch from remote

git fetch origin
git checkout <branch name>

it automatically creates local branch <branch name> with an upstream pointing to remote-tracking branch origin/<branch name>.

or (for Git < 1.6.6)

git checkout -b <branch name> origin/<branch name>

Fetch all branches from remote

git fetch origin

It fetches all the branches of origin remote into remote-tracking branches under origin/.

Fetch branch from remote

git fetch origin foo

It fetches foo branch from origin remote and put it under origin/foo.

Delete all branches already merged into the current branch

git branch --merged | grep -v "\*" | xargs -n 1 git branch -d

Replace local changes with remote's master

git reset --hard origin/master

Clone repository and all of its submodules

git clone --recursive git://github.com/foo/bar.git

For Git <= X

git clone git://github.com/foo/bar.git
cd bar
git submodule init
git submodule update

Rename branch

git branch -m <branch name> <new branch name>

Rename current branch

git branch -m <new branch name>

Delete local branch

git branch -d <branch name>

Delete branch from remote

git push origin --delete <branch name>

or

git push origin :<branch name>

Show which branch is tracking which remote branch

git remote show origin

Make an existing Git branch track a remote branch

git branch -u origin/<branch name>

or, if local <branch name> is not the current branch

git branch -u origin/<branch name> <branch name>

or, longer form

git branch --set-upstream-to=origin/<branch name>

For Git < 1.7.0

git branch --set-upstream foo upstream/foo

This syntax is now deprecated.

Show local branches

git branch -lv

Show remote branches

git branch -rv

Show stale remote-tracking branches

git remote prune origin --dry-run

Remove stale remote-tracking branches

git remote prune origin

Go to previous branch

git checkout -

Shows branches merged in current branch

git branch --merged

Shows branches not merged in to your current branch

git branch --no-merged

Remotes

Remotes are like nicknames for the URLs of repositories, e.g. origin.

Add remote

git remote add upstream git@github.com:<user name>/<project name>.git

List remotes

git remote -v

Delete remote

git remote rm <remote name>

Rebasing

Rebase on top of remote-tracking branch

git rebase origin/master

Undo a rebase

git reset --hard ORIG_HEAD

reset, rebase & merge save the original HEAD pointer into ORIG_HEAD; to undo it, use git reset --hard.

Submodules

Submodules are tracked by the exact commit specified in the parent project, not a branch, a ref, or any other symbolic reference.

Remove submodule

  1. Delete the relevant line from the .gitmodules file.
  2. Delete the relevant section from .git/config.
git rm --cached <path to submodule>
git commit
rm -rf <path to submodule>

Log

Show only the last commit in the log

git log -1

Show commits only in specific branches

git log master..feature

or

git log feature --not master

or

git log feature feature2 --not master

Show incoming commits

git log ..@{u}

(using reflog syntax available for Git >= 1.7.0)

Show outgoing commits

git log @{u}..

(using reflog syntax available for Git >= 1.7.0)

Show commits since the last pull without merges in reverse order

git log --reverse --no-merges --stat @{1}..

Search commits by author

git log --author=Zaiste

Search through commit messages

git log --grep="42 and life"

Generate changelog between releases

git shortlog release/42 ^release/41

Generate monthly commit summary for specific user

git log --pretty=format:"%h - %s <%cn> %cd" --author="<author name>" --after 2015-11-01 --before 2015-11-31 --no-merges --date=short

Diff

Show incoming changes

git diff ..@{u}

Show outgoing changes

git diff @{u}..

Show changes between branch and its remote-tracking branch

git diff master origin/master

or

git diff ...origin

Tags

Rename tag

git tag new old
git tag -d old
git push origin :refs/tags/old
git push --tags

Make sure other repository users remove the deleted tag as well. They should run the following command:

git pull --prune --tags

Varia

Use specific SSH key to clone repository

ssh-agent bash -c 'ssh-add ~/.ssh/<key file name>; git clone git@github.com:<user name>/<project name>.git’

or

ssh-agent (ssh-add ~/.ssh/<key file name>; git clone git@github.com:<user name>/<project name.git)

TBC...

Suggestions, adjustments or corrections are welcome!

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