Revision specifiers

SHA-1 or short SHA-1 (default first seven characters)
Branch name
RefLog shortnames, works for HEAD and branch names. ‘git reflog’ to see list or ‘git reflog show master’
- HEAD@{5} fifth HEAD ago
- master@{yesterday}
- @{upstream} current branch origin
HEAD^ parent of HEAD
d921970^2 second parent of d921970, only useful for merges. does not mean grandparent
HEAD~ parent of HEAD (equivalent to HEAD^)
HEAD~2 grandparent of HEAD (equivalent to HEAD^^)
A..B commits in B that are not in A
A.. equivalent to A..HEAD (also ..B)
A…B commits in either but not both, often with –left-right

Bisect

Use git bisect to quickly determine what commit introduced a change, usually a bug.

git bisect start
git bisect good a1b54ff3 Mark an earlier commit that works
git bisect bad master Mark a later commit that doesn’t work
- Repeatedly test the checkouts, running git bisect bad|good|skip for each
Eventually, git will report the first commit that broke
git bisect reset To end the session

Attributes

Attributes can mark files as machine generated, non-diffable, non-mergable, etc
Attributes specified in .gitattributes can be overridden in .git/info/attributes

Change branch without tree

This will update the current branch, without changing any files. The difference between the two points will be left as uncommitted changes.

git checkout workingTree
git checkout --detach
git reset --mixed destination
git checkout destination

Diff

Git’s diff can be used on arbitrary files or folders, even if they are in separate repos or no repos at all.

git diff --no-index current/ base/

Merge to squash

This re-writes a traditional merge commit into a squashed merge commit. Any dependent tree’s will have to be rebased onto the new commit. Also this will require force push.

Have the merge commit branch checked out
git reset --hard HEAD~1
git cherry-pick -m 1 HEAD@{1}

Interop with an svn repo

git svn clone <svn url> -s --prefix=origin/
git svn clone <svn url>/trunk --prefix=origin/ # clone without tags and branches
git svn fetch # gets new svn commits onto origin/git-svn, can continue a failed clone sometimes
# ...use git normally...
git svn rebase # pulls down, rebases current work on top, creates local commits. instead of pull
git svn dcommit
# ...if using topic branches, rebase them onto master instead of merging.
# ...don't push to git repos, since commits get rewritten when using dcommit
git svn find-rev r1234

Rebase stacked branches

Adapted from Git rebase docs

In the following situation, there is a stacked feature branch, and topicA has been squash merged to main. We want to rebase the commits from topicB back onto main.

                        H---I---J topicB
                       /
              E---F---G  topicA
             /
A---B---C---D---EFG’  main

The command git rebase --onto main topicA topicB makes the following change

                   E---F---G  topicA
                 /      H'--I'--J'  topicB
                |     /
    A---B---C---D---EFG’  main

This could also be useful when topicB does not depend on topicA, regardless of topicA being merged.