Git

Last Updated: 2023-01-15

"Repos" and "Areas"

• the working copy: where you are editing and building (not committed yet to your repo).
• staging area / index
• local repo: your own repository with your own commit history.
• local "cached" copy of a remote repository.
• remote repo.

The staging area (index) is shared by all branches; committed code (in local repository) is per branch. So it doesn't matter what branch you're on when you add a file.

Working Tree

• Discard changes: git restore.

Working Tree <=> Staging Area

• Working Tree => Staging Area: git add / git rm
• Staging Area => Working Tree (Unstage): git reset HEAD / git restore --staged <file>

Staging Area <=> Local Repo

• Staging Area => Local Repo: git commit
• Local Repo => Staging Area / Working Tree:
  • git reset --soft HEAD^ (files are still staged)
  • git reset HEAD^ (files are no longer stage, but still in the working area)
  • git reset --hard HEAD^ (changes are thrown away, not even in the working tree)

Local Repo <=> Remote Repo

• Local Repo => Remote Repo: git push
• Remote Repo => Local Repo: git fetch

Concepts

Branch

In Git, a branch is a pointer to one specific commit, while a commit is a snapshot of your repository at a specific point in time.

# show local branches
$ git branch

# show remote branches
$ git branch -r

# show both local and remote branches
$ git branch -a

HEAD

HEAD: "Where am I right now?"

Most of the time, HEAD points to a branch name. HEAD is synonymous with "the last commit in the current branch."

• attached: in the normal state, HEAD is attached to a branch.
• detached: HEAD is pointing directly to a commit instead of a branch.

Workflow

# Pull updates from remote
$ git pull origin main --rebase

# Commit local changes
$ git add -A
$ git commit --amend

# Push
$ git push origin main

Checkout a Remote Branch

$ git fetch
$ git checkout test

or

$ git checkout -b <branch> --track <remote>/<branch>

Diff

$ git diff ...origin

Config

Config file location:

• Global: ~/.gitconfig
• System: /etc/gitconfig
• Local: /git/configcoding

Set a name

$ git config --global user.name "My Name"
$ git config --local user.name "Foo Bar"

Show the name

$ git config --local user.name
Foo Bar

Tags

List all tags:

$ git tag -l
1.0.0

Checkout a tag:

$ git checkout tags/<tag_name>
$ git checkout tags/1.0.0

Remove a tag:

# remove local tag
$ git tag -d <tag_name>

# remove remote tag
$ git push origin :[tag]
$ git push origin :refs/tags/<tag_name>

Add All

To add everything to stage, including additions and removals, use

$ git add -A

Undo commits

$ git reset HEAD~1

Now all the changes done in that commit are unstaged and need to be committed again.

Abandon Changes

Abandon changes and revert your tree to the "clean" state of your current branch. Don't use git revert, use:

# Go back to HEAD
$ git reset --hard HEAD

# Go back to the commit before HEAD
# i.e. abandon the top most commit
$ git reset --hard HEAD^

# Equivalent to "HEAD^"
$ git reset --hard HEAD~1

# Go back two commits before HEAD
$ git reset --hard HEAD~2

# Go back to origin/HEAD
$ git reset --hard origin/HEAD

To revert changes made to your working copy

$ git restore .

To uncommit but does not revert local changes

$ git reset HEAD~

To uncommit and revert local changes

$ git reset HEAD~ --hard

Reset to a remote branch

$ git fetch origin
$ git reset --hard origin/master

In increasing order of dangerous-ness:

• --soft: moves HEAD but doesn't touch the staging area or the working tree.
• --mixed: moves HEAD and updates the staging area, but not the working tree.
• --merge: moves HEAD, resets the staging area, and tries to move all the changes in your working tree into the new working tree.
• --hard: moves HEAD and adjusts your staging area and working tree to the new HEAD, throwing away everything.

Upstream Remote

Add your own fork as origin remote

$ git remote add origin https://github.com/<your_fork>/<project_name>.git

Add the central repo as upstream remote

$ git remote add upstream https://github.com/<central_repo>/<project_name>.git

To sync up with upstream

$ git fetch upstream
$ git merge upstream/develop

Or

$ git pull upstream develop

Config global user name and email

Global config is in $HOME/.gitconfig; per repo config is in .git/config.

$ git config --global user.name <your_name>
$ git config --global user.email <[email protected]>

Commit in Wrong User/Email

If user is specified in .git/config as

[user]
    name = your_name
    email = [email protected]

however if git is using the wrong user settings after commit

Author: your_name <[email protected]>

Check if you have these settings in env

• GIT_AUTHOR_NAME
• GIT_AUTHOR_EMAIL
• GIT_COMMITER_NAME
• GIT_COMMITER_EMAIL

Remove those then try again

How do I make Git ignore file mode (chmod) changes?

$ git config core.fileMode false

or

$ git config --global core.filemode false

or open .git/config and modify the core section.

Force Push to head

Override the remote HEAD

$ git push origin +HEAD^:master

Show Remote Logs

$ git log origin/main

Cherrypick

cherry-pick: pick one change from anywhere in the repository and will apply it on your local branch.

export BRANCH=<branch to cherrypick>

git fetch origin
git checkout ${BRANCH}
git cherry-pick ${SHA}

git push origin HEAD:refs/for/${BRANCH}

git apply

# generate diff
git diff filename
git diff > my_patch.patch

# apply diff; will fail with conflicts
git apply my_patch.patch

# apply diff; ask to resolve conflicts
git apply --3way my_patch.patch