dev-notes/docs/git/git.md

Git

Glossary

GIT: an open source, distributed version-control system
GITHUB: a platform for hosting and collaborating on Git repositories

TREE: directory that maps names to blobs or trees
BLOB: any file
COMMIT: snapshot of the entire repository + metadata, identified it's SHA-1 hash

HEAD: represents the current working directory, the HEAD pointer can be moved to different branches, tags, or commits when using git checkout
BRANCH: a lightweight movable pointer to a commit
CLONE: a local version of a repository, including all commits and branches
REMOTE: a common repository on GitHub that all team member use to exchange their changes

FORK: a copy of a repository on GitHub owned by a different user
PULL REQUEST: a place to compare and discuss the differences introduced on a branch with reviews, comments, integrated tests, and more

REPOSITORY: collection of files and folder of a project aka repo
STAGING AREA/STASH: area of temporary snapshots (not yet commits)

Data Model

Data Model Structure:

<root> (tree)
|
|_ foo (tree)
|  |_ bar.txt (blob, contents = "hello world")
|
|_ baz.txt (blob, contents = "git is wonderful")

Data Model as pseudocode:

# a file is a bunch of bytes
blob = array<byte>

# a directory contains named files and directories
tree = map<string, tree | file>

# a commit has parents, metadata, and the top-level tree
commit = struct {
    parent: array<commit>
    author: string
    message: string
    snapshot: tree
}

# an object is either a blob, tree or commit
object = map<string, blob | tree | commit>

# commit identified by it's hash (unmutable)
def store(object):
    id = sha1(object)  # hash repo
    objects<id> = object  # store repo w/ index hash

# load the commit
def load(id):
    return objects<id>

# human-readable names for SHA-1 hashes (mutable)
references = map<string, string>

# bind a reference to a hash
def update_reference(name, id):
    references<name> = id

def read_reference(name):
    return references<name>

def load_reference(name_or_id):
    if name_or_id in references:
        return load(references<name_or_id>)
    else:
        return load(name_or_id)

Commands

git help <command>: get help for a git command

Create Repository

git init [<project_name>]: initialize a brand new Git repository and begins tracking
.gitignore: specify intentionally untracked files to ignore

Config

git config --global user.name "<name>": set name attached to commits
git config --global user.email "<email address>": set email attached to commits
git config --global color.ui auto: enable colorization of command line output

Making Changes

git status: shows the status of changes as untracked, modified, or staged
git add <filename1 filename2 ...>: add files to the staging area
git add -p <files>: interactively stage chunks of a file

git blame <file>: show who last edited which line

git commit: save the snapshot to the project history
git commit -m "message": commit and provide a message
git commit -a: automatically notice any modified (but not new) files and commit
git commit -v|--verbose: show unified diff between the HEAD commit and what would be committed

git diff <filename>: show difference since the last commit
git diff <commit> <filename>: show differences in a file since a particular snapshot
git diff <reference_1> <reference_2> <filename>: show differences in a file between two snapshots
git diff --cached: show what is about to be committed
git diff <first-branch>...<second-branch>: show content diff between two branches

git bisect: binary search history (e.g. for regressions)

Stashes

git stash [push -m|--message]: add all changes to the stash (and provide message)
git stash list list all stashes
git stash show [<stash>]: show changes in the stash
git stash pop: restore last stash
git stash drop [<stash>]: remove a stash from the list
git stash clear: remove all stashes

Remotes

git remote: list remotes
git remote -v: list remotes names and URLs
git remote show <remote>: inspect the remote

git remote add <remote> <url | path>: add a remote
git branch --set-upstream-to=<remote>/<remote branch>: set up correspondence between local and remote branch

git push <remote> <branch>: send objects to remote
git push <remote> <local branch>:<remote branch>: send objects to remote, and update remote reference

git fetch [<remote>]: retrieve objects/references from a remote
git pull: update the local branch with updates from its remote counterpart, same as git fetch; git merge
git pull -ff: when possible resolve the merge as a fast-forward (only update branch pointer, don't create merge commit). Otherwise create a merge commit.

git fetch && git show <remote>/<branch>: show incoming changes

git clone <url> [<folder_name>]: download repository and repo history from remote
git clone --shallow: clone only repo files, not history of commits

git remote remove <remote>: remove the specified remote
git remote rename <old_name> <new_name>: rename a remote

Viewing Project History

git log: show history of changes
git log -p: show history of changes and complete differences
git log --stat --summary: show overview of the change
git log --follow <file>: list version history fo file, including renames
git log --all --graph --decorate: visualizes history as a DAG
git log --oneline: compact log

git shortlog: list commits by author

git show <commit>: output metadata and content changes of commit
git cat-file -p <commit>: output commit metadata

Tag

Git supports two types of tags: lightweight and annotated.

A lightweight tag is very much like a branch that doesn't change—it's just a pointer to a specific commit.

Annotated tags, however, are stored as full objects in the Git database.
They're checksummed;contain the tagger name, email, and date; have a tagging message; and can be signed and verified with GNU Privacy Guard (GPG).
It's generally recommended creating annotated tags so it's possible to have all this information.

git tag: list existing tags
git tag -l|--list <pattern>: list existing tags matching a wildcard or pattern

git tag <tag> [<commit_hash>]: create a lightweight tag on the commit
git tag -a <tag> [<commit_hash> -m <message>]: create am annotated tag on the commit

git push <remote> <tagname>: push a tag to the remote
git push <remote> --tags: push commits and their tags (both types) to the remote

git tag -d <tagname>: delete a tag
git push <remote> :refs/tags<tagname>:: remove a tag from the remote
git push <remote> --delete <tagname>: remove a tag from the remote

git checkout <tag>: checkout a tag - WARNING: will go into detached HEAD

Branching And Merging

git branch: shows branches
git branch -v: show branch + last commit

git branch <branch-name>: create new branch
git checkout -b <branch-name>: create a branch and switches to it, same as git branch <name>; git checkout <name>
git branch: show list of all existing branches (* indicates current)
git checkout <branch-name>: change current branch (update HEAD) and update working directory
git branch -d <branch-name>: delete specified branch
git branch -m <old_name> <new_name>: rename a branch without affecting the branch's history

git merge <branch-name>: merges into current branch
git merge --continue: continue previous merge after solving a merge conflict
git mergetool: use a fancy tool to help resolve merge conflicts
git rebase: rebase set of patches onto a new base
git rebase -i: interactive rebasing

git cherry-pick <commit>: bring in a commit from another branch git cherry-pick <commit>^..<commit>: bring in a range of commits from another branch (first included) git cherry-pick <commit>..<commit>: bring in a range of commits from another branch (first excluded)

Undo & Rewriting History

git commit --amend: replace last commit by creating a new one (can add files or rewrite commit message)
git commit --amend -m "amended message": replace last commit by creating a new one (can add files or rewrite commit message)
git commit --amend --no-edit: replace last commit by creating a new one (can add files or rewrite commit message)
git reset HEAD <file>: unstage a file
git reset <commit>: undo all commits after specified commit, preserving changes locally
git checkout <file>: discard changes
git checkout -- <file>: discard changes, no output to screen
git reset --soft <commit>: revert to specific commit but keep changes and staged files
git reset --hard <commit>: discard all history and changes back to specified commit
git rebase -i HEAD~<n>: modify (reword, edit, drop, squash, merge, ...) n commits git rm --cached <file>: remove a file from being tracked

WARNING: Changing history can have nasty side effects

---

How To

Rebase Branches

git checkout <primary_branch>
git pull  # get up to date

git checkout <feature_branch>
git rebase <primary_branch>  # rebase commits on master (moves branch start point on last master commit)

git checkout <primary_branch>
git rebase <feature_branch>  # moves commits from the branch on top of master

Clone Branches

git clone <repo>  # clone the repo

git branch -r  # show remote branches
git checkout <branch>  # checkout remote branch (omit <remote>/)

git pull  # clone branch

Sync Forks

git fetch upstream  # Fetch the branches and their respective commits from the upstream repository
git checkout main  # checkout fork's main primary branch

git merge upstream/main  # Merge the changes from the upstream default branch into the local default branch

git push  #  update fork on GitHub