mirror of
https://github.com/m-lamonaca/dev-notes.git
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267 lines
10 KiB
Markdown
267 lines
10 KiB
Markdown
# Git
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## Glossary
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**GIT**: an open source, distributed version-control system
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**GITHUB**: a platform for hosting and collaborating on Git repositories
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**TREE**: directory that maps names to blobs or trees
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**BLOB**: any file
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**COMMIT**: snapshot of the entire repository + metadata, identified it's SHA-1 hash
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**HEAD**: represents the current working directory, the HEAD pointer can be moved to different branches, tags, or commits when using git checkout
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**BRANCH**: a lightweight movable pointer to a commit
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**CLONE**: a local version of a repository, including all commits and branches
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**REMOTE**: a common repository on GitHub that all team member use to exchange their changes
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**FORK**: a copy of a repository on GitHub owned by a different user
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**PULL REQUEST**: a place to compare and discuss the differences introduced on a branch with reviews, comments, integrated tests, and more
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**REPOSITORY**: collection of files and folder of a project aka repo
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**STAGING AREA/STASH**: area of temporary snapshots (not yet commits)
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## Data Model
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Data Model Structure:
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```txt
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<root> (tree)
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|_ foo (tree)
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| |_ bar.txt (blob, contents = "hello world")
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|_ baz.txt (blob, contents = "git is wonderful")
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```
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Data Model as pseudocode:
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```py
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# a file is a bunch of bytes
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blob = array<byte>
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# a directory contains named files and directories
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tree = map<string, tree | file>
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# a commit has parents, metadata, and the top-level tree
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commit = struct {
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parent: array<commit>
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author: string
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message: string
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snapshot: tree
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}
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# an object is either a blob, tree or commit
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object = map<string, blob | tree | commit>
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# commit identified by it's hash (unmutable)
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def store(object):
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id = sha1(object) # hash repo
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objects<id> = object # store repo w/ index hash
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# load the commit
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def load(id):
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return objects<id>
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# human-readable names for SHA-1 hashes (mutable)
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references = map<string, string>
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# bind a reference to a hash
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def update_reference(name, id):
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references<name> = id
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def read_reference(name):
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return references<name>
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def load_reference(name_or_id):
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if name_or_id in references:
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return load(references<name_or_id>)
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else:
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return load(name_or_id)
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```
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## Commands
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`git help <command>`: get help for a git command
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### Create Repository
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`git init [<project_name>]`: initialize a brand new Git repository and begins tracking
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`.gitignore`: specify intentionally untracked files to ignore
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### Config
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`git config --global user.name "<name>"`: set name attached to commits
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`git config --global user.email "<email address>"`: set email attached to commits
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`git config --global color.ui auto`: enable colorization of command line output
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### Making Changes
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`git status`: shows the status of changes as untracked, modified, or staged
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`git add <filename1 filename2 ...>`: add files to the staging area
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`git add -p <files>`: interactively stage chunks of a file
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`git blame <file>`: show who last edited which line
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`git commit`: save the snapshot to the project history
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`git commit -m "message"`: commit and provide a message
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`git commit -a`: automatically notice any modified (but not new) files and commit
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`git commit -v|--verbose`: show unified diff between the HEAD commit and what would be committed
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`git diff <filename>`: show difference since the last commit
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`git diff <commit> <filename>`: show differences in a file since a particular snapshot
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`git diff <reference_1> <reference_2> <filename>`: show differences in a file between two snapshots
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`git diff --cached`: show what is about to be committed
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`git diff <first-branch>...<second-branch>`: show content diff between two branches
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`git bisect`: binary search history (e.g. for regressions)
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### Stashes
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`git stash [push -m|--message]`: add all changes to the stash (and provide message)
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`git stash list` list all stashes
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`git stash show [<stash>]`: show changes in the stash
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`git stash pop`: restore last stash
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`git stash drop [<stash>]`: remove a stash from the list
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`git stash clear`: remove all stashes
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### Remotes
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`git remote`: list remotes
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`git remote -v`: list remotes names and URLs
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`git remote show <remote>`: inspect the remote
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`git remote add <remote> <url | path>`: add a remote
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`git branch --set-upstream-to=<remote>/<remote branch>`: set up correspondence between local and remote branch
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`git push <remote> <branch>`: send objects to remote
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`git push <remote> <local branch>:<remote branch>`: send objects to remote, and update remote reference
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`git fetch [<remote>]`: retrieve objects/references from a remote
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`git pull`: update the local branch with updates from its remote counterpart, same as `git fetch; git merge`
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`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.
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`git fetch && git show <remote>/<branch>`: show incoming changes
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`git clone <url> [<folder_name>]`: download repository and repo history from remote
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`git clone --shallow`: clone only repo files, not history of commits
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`git remote remove <remote>`: remove the specified remote
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`git remote rename <old_name> <new_name>`: rename a remote
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### Viewing Project History
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`git log`: show history of changes
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`git log -p`: show history of changes and complete differences
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`git log --stat --summary`: show overview of the change
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`git log --follow <file>`: list version history fo file, including renames
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`git log --all --graph --decorate`: visualizes history as a DAG
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`git log --oneline`: compact log
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`git shortlog`: list commits by author
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`git show <commit>`: output metadata and content changes of commit
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`git cat-file -p <commit>`: output commit metadata
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### Tag
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Git supports two types of tags: *lightweight* and *annotated*.
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A lightweight tag is very much like a branch that doesn't change—it's just a pointer to a specific commit.
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Annotated tags, however, are stored as full objects in the Git database.
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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).
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It's generally recommended creating annotated tags so it's possible to have all this information.
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`git tag`: list existing tags
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`git tag -l|--list <pattern>`: list existing tags matching a wildcard or pattern
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`git tag <tag> [<commit_hash>]`: create a *lightweight* tag on the commit
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`git tag -a <tag> [<commit_hash> -m <message>]`: create am *annotated* tag on the commit
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`git push <remote> <tagname>`: push a tag to the remote
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`git push <remote> --tags`: push commits and their tags (both types) to the remote
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`git tag -d <tagname>`: delete a tag
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`git push <remote> :refs/tags<tagname>:`: remove a tag from the remote
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`git push <remote> --delete <tagname>`: remove a tag from the remote
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`git checkout <tag>`: checkout a tag - **WARNING**: will go into *detached HEAD*
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### Branching And Merging
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`git branch`: shows branches
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`git branch -v`: show branch + last commit
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`git branch <branch-name>`: create new branch
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`git checkout -b <branch-name>`: create a branch and switches to it, same as `git branch <name>; git checkout <name>`
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`git branch`: show list of all existing branches (* indicates current)
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`git checkout <branch-name>`: change current branch (update HEAD) and update working directory
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`git branch -d <branch-name>`: delete specified branch
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`git branch -m <old_name> <new_name>`: rename a branch without affecting the branch's history
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`git merge <branch-name>`: merges into current branch
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`git merge --continue`: continue previous merge after solving a merge conflict
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`git mergetool`: use a fancy tool to help resolve merge conflicts
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`git rebase`: rebase set of patches onto a new base
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`git rebase -i`: interactive rebasing
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`git cherry-pick <commit>`: bring in a commit from another branch
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`git cherry-pick <commit>^..<commit>`: bring in a range of commits from another branch (first included)
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`git cherry-pick <commit>..<commit>`: bring in a range of commits from another branch (first excluded)
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### Undo & [Rewriting History](https://www.themoderncoder.com/rewriting-git-history/)
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`git commit --amend`: replace last commit by creating a new one (can add files or rewrite commit message)
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`git commit --amend -m "amended message"`: replace last commit by creating a new one (can add files or rewrite commit message)
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`git commit --amend --no-edit`: replace last commit by creating a new one (can add files or rewrite commit message)
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`git reset HEAD <file>`: unstage a file
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`git reset <commit>`: undo all commits after specified commit, preserving changes locally
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`git checkout <file>`: discard changes
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`git checkout -- <file>`: discard changes, no output to screen
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`git reset --soft <commit>`: revert to specific commit but keep changes and staged files
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`git reset --hard <commit>`: discard all history and changes back to specified commit
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`git rebase -i HEAD~<n>`: modify (reword, edit, drop, squash, merge, ...) *n* commits
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`git rm --cached <file>`: remove a file from being tracked
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**WARNING**: Changing history can have nasty side effects
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---
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## How To
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### Rebase Branches
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```ps1
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git checkout <primary_branch>
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git pull # get up to date
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git checkout <feature_branch>
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git rebase <primary_branch> # rebase commits on master (moves branch start point on last master commit)
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git checkout <primary_branch>
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git rebase <feature_branch> # moves commits from the branch on top of master
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```
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### Clone Branches
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```ps1
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git clone <repo> # clone the repo
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git branch -r # show remote branches
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git checkout <branch> # checkout remote branch (omit <remote>/)
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git pull # clone branch
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```
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### [Sync Forks](https://docs.github.com/en/free-pro-team@latest/github/collaborating-with-issues-and-pull-requests/syncing-a-fork)
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```ps1
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git fetch upstream # Fetch the branches and their respective commits from the upstream repository
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git checkout main # checkout fork's main primary branch
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git merge upstream/main # Merge the changes from the upstream default branch into the local default branch
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git push # update fork on GitHub
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```
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