Git

git cat-file -p HEAD          # the commit object: tree, parent, author
git cat-file -p HEAD^{tree}   # its directory listing
git rev-parse HEAD            # resolve a ref to a SHA

git status -sb                                        # short status plus tracking info
git log --oneline --graph --decorate --all            # topology at a glance
git log --since='2 weeks' --author=jodis --stat
git log -p -- path/to/file                            # history of one file, with diffs
git log --follow -- path/to/file                      # ...across renames
git log -S 'AWS_SECRET' --oneline                     # commits that add or remove a string
git log -G 'regex' --oneline                          # commits whose diff matches a regex
git log --grep 'JIRA-123' --oneline                   # commits whose message matches
git log main..feature --oneline                       # in feature, not in main
git log --left-right --oneline main...feature         # divergence on both sides
git show <sha> --stat
git blame -L 20,40 -- file
git diff main...feature                               # changes since the branches diverged

git restore --source main -- config/app.yaml    # one file from another branch
git revert -m 1 <merge-sha>                     # revert a merge, keeping mainline 1
git reset --hard origin/main                    # make local match remote exactly
git clean -nd                                   # preview untracked removal
git clean -fd                                   # remove untracked files and directories

git reflog                                # HEAD movements with reasons
git reflog show feature-x                 # one branch's movements
git reset --hard HEAD@{2}                 # back to where you were two moves ago
git branch rescue <sha-from-reflog>       # recover a deleted branch
git fsck --lost-found                     # dangling commits, when even reflog was pruned

git switch -c feature-x                   # create and switch (modern spelling)
git switch -                              # previous branch
git switch --detach <sha>                 # look around without moving a branch
git branch -vv                            # local branches and their upstreams
git branch --merged main                  # already in main: safe to delete
git branch --no-merged main               # still carrying unique commits
git push -u origin feature-x              # push and set upstream
git push origin --delete feature-x
git fetch --prune                         # drop remote-tracking refs that no longer exist

# Delete every local branch already merged into main
git branch --merged main | grep -vE '^\*|main|master' | xargs -r git branch -d

git fetch origin
git rebase origin/main                    # replay my commits on top of main
git rebase -i origin/main                 # squash, reword, drop, reorder
git rebase --continue | --skip | --abort
git merge --no-ff feature-x               # keep the branch's shape in history
git merge --squash feature-x              # one commit, no merge record
git pull --rebase                         # avoid merge commits from pulling
git config --global pull.rebase true

git status                                # "both modified" lists the conflicts
git diff --diff-filter=U                  # only unresolved files
git checkout --ours -- file               # keep the current branch's version
git checkout --theirs -- file             # keep the incoming version
git add file && git rebase --continue
git merge --abort                         # back to before the merge
git rerere status                         # replay a previously recorded resolution
git config --global rerere.enabled true

git stash push -u -m 'wip: auth refactor'  # -u includes untracked files
git stash list
git stash show -p stash@{0}
git stash pop                              # apply and drop
git stash apply stash@{1}                  # apply and keep
git stash branch fix-auth stash@{0}        # turn a stash into a branch

git worktree add ../hotfix hotfix          # second checkout, same repository
git worktree list
git worktree remove ../hotfix

git remote -v
git remote set-url origin git@github.com:example/repo.git
git config --global credential.helper 'cache --timeout=3600'
git config --global url."git@github.com:".insteadOf "https://github.com/"
git clone --filter=blob:none <url>        # partial clone: history without old blobs
git clone --depth 1 <url>                 # shallow, for CI
git fetch --unshallow                     # turn a shallow clone into a full one

git tag -a v1.4.2 -m 'release 1.4.2'      # annotated: has an author, date and message
git tag -l 'v1.*' --sort=-v:refname
git push origin v1.4.2
git push origin --tags
git tag -d v1.4.2 && git push origin :refs/tags/v1.4.2
git describe --tags --always              # human-readable version from the nearest tag

git bisect start
git bisect bad                             # current commit is broken
git bisect good v1.4.0                     # this one was fine
# ...test, then mark each step
git bisect run ./test.sh                   # or automate: exit 0 = good, non-zero = bad
git bisect reset

git config --global user.name 'Jodis Fields'
git config --global user.email 'you@example.com'
git config --global commit.gpgsign true
git config --global init.defaultBranch main
git config --global core.excludesFile ~/.gitignore
git config --global rebase.autosquash true
git config --list --show-origin           # which file set what

# .git/hooks/pre-commit — reject obvious secrets
#!/usr/bin/env bash
if git diff --cached -U0 | grep -nE 'AKIA[0-9A-Z]{16}|BEGIN (RSA|OPENSSH) PRIVATE KEY'; then
  echo 'possible credential in staged changes' >&2
  exit 1
fi

# Branches by last commit date, newest first
git for-each-ref --sort=-committerdate refs/heads --format='%(committerdate:short) %(refname:short) %(authorname)'

# Commits per author, excluding merges
git shortlog -sn --no-merges

# Files changed most often
git log --format=format: --name-only | sort | uniq -c | sort -rn | head

# Largest objects in the repository
git rev-list --objects --all | git cat-file --batch-check='%(objecttype) %(objectname) %(objectsize) %(rest)' | awk '$1=="blob"' | sort -k3 -nr | head

# What landed between two tags
git log --oneline --no-merges v1.4.0..v1.5.0

# Everything that touched a directory last month
git log --since='1 month' --oneline -- infra/

# Which branches contain a commit
git branch -a --contains <sha>

# The commit that introduced a string
git log -S 'deprecatedFlag' --oneline --reverse | head -1

# Diff ignoring whitespace churn
git diff -w --ignore-blank-lines

# Show a file as it was at a date
git show 'HEAD@{2024-01-15}:path/to/file'

# Apply one commit from another branch
git cherry-pick -x <sha>

# Stage only part of a file
git add -p file

# Rewrite author on the last commit after fixing config
git commit --amend --reset-author --no-edit

# Repository size and object count
git count-objects -vH

# Prune and repack a bloated clone
git gc --prune=now --aggressive