MakingGitWorkForYou

• Wifi: RAV-TRAINING
• Password: Solve Challenges
• http://xkcd.com/1597/
• Hover text: If that doesn’t fix it, git.txt
contains the phone number of a
friend of mine who understands git.
Just wait through a few minutes of
“It’s really pretty simple, just think of
branches as…” and eventually you’ll
learn the commands that will fix
everything.
• Slides + Demo Code:
• https://github.com/Kwen/sfdevs

Making Git Work For You
Kwen Peterson
Senior Software Developer @ Raven
kwen.peterson@gmail.com
@kwenarik

"You're already in the top tier of developers just
by showing up here tonight. I don't know how
talented you are, how much experience you have,
but you showed up. You're putting yourself out
there because you care to improve. Thanks for
caring.“ – Scott Hanselman

Rebase vs. Merge
• Merging brings two lines of development together while
preserving the ancestry of each commit history.
• In contrast, rebasing unifies the lines of development by
re-writing changes from the source branch so that they
appear as children of the destination branch – effectively
pretending that those commits were written on top of the
destination branch all along.
– Rebase requires the commits on the source branch to be re-
written, which changes their content and their SHAS.

The merge DNA helix vs. rebase OCD

Commit graph (pure rebase with ff)

Merge
• Pros
– Simpler to use and understand
– The commits on the source branch remain separate from
other branch commits, provided you don’t perform a fast-
forward merge. (This separation can be useful in the case
of feature branches, where you might want to take a
feature and merge it into another branch later.)
– Existing commits on the source branch are unchanged and
remain valid; it doesn’t matter if they’ve been shared.
• Cons
– If the need to merge arises simply because multiple people
are working on the same branch in parallel, the merges
don’t serve any useful historical purpose & create clutter.

Rebase
• Pros
– Simplifies your history.
– Is the most intuitive and clutter-free way to combine
commits from multiple developers in a shared branch.
• Cons
– Slightly more complex, conflicts require resolution on
a per commit basis.
– Rewriting of history has ramifications if you’ve
previously pushed those commits elsewhere.

Why does my boss/team care?
• Merging
– Merge conflicts between your changes and others doesn’t
happen until you merge back into master and resolve them
there, with new commits that happen after the merge commit.
– You are testing your changes in isolation until you merge with
master
• Rebasing
– Merge conflicts between your changes and others happens in
your feature branch and are resolved in your feature branch.
– You are testing your changes with the latest changes from
master in your topic branch.

When should I rebase?
• Fine fine fine. You’ve convinced me to try out this
“rebase” thing. How often / when should I rebase
changes from master into my feature branch?
– Every morning? Wait until I have my feature branch working in
isolation and then do one monster rebase resolving 2 months
worth of differences?
• “It depends.” 
– In my 6.5 years of experience with git, it seems to amount to the
same time/effort either way. You either pay for it in smaller ~10
minute chunks, or in one massive, 2 hour long rebase session at
the end.

Let’s talk about merge conflicts…

Merge Conflicts!
• Git rebase origin/master
• Hit a conflict  git mergetool
• Ok, everything’s fixed  git rebase --continue
– (loop)
• Crap! I messed that up and need to bail out!  git rebase --abort
• Hmm, looks like I made the exact same change in my topic branch
as was already made in master, I need to skip this commit and keep
rebasing  git rebase --skip
• If you have issues with a merge and want to revert it while the
merge is in progress, the equivalent is git reset HEAD --hard.
– Remember, rebase applies commits one at a time and makes you deal with any
conflicts one at a time. Merge simply looks at the <initial state> vs. <cumulative
end state> and gives you a single, massive set of changes to resolve!

Merge Conflicts
• git merge <branch> (git merge feature-47_fixed-stuff)
– Merge changes in the specified branch onto the current branch
– In a merge conflict branch you are ON is local, branch specified in the
merge is remote.
• git rebase <remote>/<branch> (git rebase origin/master)
– Base the current branch you are on off the specified remote branch
– Takes the specified branch as the base, and then applies any changes
you have in your local branch on top of that. For conflicts, the current
branch is called remote, and the branch you specified is treated as local.
• Assuming you are merging feature branches into master or rebase
feature branches with master, local = master, remote = feature in
both situations.

Interactive Rebase (Squash)
• git rebase –i HEAD~3
– pick f392171 Added new feature X
– pick ba9dd9a Added new elements to page design
– pick df71a27 Updated CSS for new elements
• Change to:
– pick f392171 Added new feature X
– squash ba9dd9a Added new elements to page
design
– squash df71a27 Updated CSS for new elements

(Or git push –f origin master Or git push origin +master:master)
Golden Rule of Rebasing: NEVER EVER* rebase a branch that you
already pushed or that you pulled from another person.
* Except for when you truly want/need to rewrite the history of your repository.

git reflog
• Uses VIM navigation controls: J = down arrow, K = up arrow, Q = quit
• Use the commit hashes, not the HEAD positions! To go back in time and return your
current branch to a prior state, the syntax is git reset 2a7d231 --hard. (This will
return you to the point before the last 2 rebases in the above screenshot.)

Detached Heads, Submodules
• Detached Head – Tracking a specific commit,
not a branch!
– If git was a book:
• HEAD is where your finger is (current spot)
• Branches are where you put your bookmarks
– If you close the book without a bookmark on that page, you
lose your spot!
• Submodules – Shared ‘child’ git repository
(notorious for detached HEAD issues…)

What does a detached head look like?

git worktree (new in 2.5.0)
• Who here has a co-worker that instead of
swapping branches just pulls down multiple
copies of the repo into different folders?
– Allows you to checkout multiple branches
simultaneously (master + sprint/feature)
• Instead of stash, you can you this!
– git worktree add -b hotfix ../hotfix origin/master
• After work/commits are done, simply delete the /hotfix folder!
– All worktree branches use the “parents” .git repo
• Saves space, all worktree branches are dumb/disposable

2nd Order Diff Trick
• Migrating Textile URLs to Markdown using Regex
– s{"(.+?)":([^.,:s]+)}{[$1]($2)}g  Not even close
– s{"(.+?)":([^.,!)]s]+)}{[$1]($2)}g  Not even close
– s{"(.+?)":([^,!)]s]+)b}{[$1]($2)}g  Getting closer
– s{"(.+?)":([^,!)]s]+)}{[$1]($2)}g  Pretty close!
• git stash save “almost there”
– s{"(.+?)":([^,!)]s]+)}{my($t,$l)=($1,$2);$l=~/(.*?)([.:])?$/;
"[$t]($1)$2"}eg  “minor tweak”
• git diff ‘stash@{0}’
– http://blog.moertel.com/posts/2013-02-18-git-second-order-diff.html

Filter Branch
• git filter-branch --force --index-filter 'git rm --
cached -r --ignore-unmatch MY-BIG-
DIRECTORY-OR-FILE' --prune-empty --tag-
name-filter cat -- --all
– This is SLOW.
– You have to use the full path to the file/folder you
want filtered out.
– You would have to run it twice for /bin/OpenId.dll &
/bin/debug/OpenId.dll (or generate a file with all the
path/filenames, then script it against the above.)

BFG Repo Cleaner
• Written in Scala, requires JVM 7+
• Much faster (10-720x faster)
• Much easier to use (alias java -jar bfg.jar to bfg)
– bfg --delete-files EntityFramework.dll my-repo.git
• Purge EntityFramework.dll out of the 105 bin folders in my
solution in one easy, readable command.
– bfg --strip-blobs-bigger-than 10M my-repo.git
• Purges any file from history that was ever larger than 10Mb
– bfg --delete-files id_{dsa,rsa} my-repo.git
• Purges id_rsa & id_dsa files from any path and point in time
– bfg --delete-folders bin my-repo.git

BFG
• git clone --mirror <old_remote>
• bfg –delete-files Quartz.dll my-repo.git
– <repeat>, inspect your changes. If happy proceed!
• git gc
• cd my-repo.git
• git reflog expire --expire=now --all && git gc --
prune=now –aggressive
• git push <new_remote>

Git LFS Cheatsheet
• Install the commandline git extension, then run
git lfs install or git lfs init
• git lfs track “*.psd”
– Only works going forward, you will have to use BFG
or filter branch to retroactively purge any already
committed large files!
– git-lfs fetch (get me the ACTUAL huge files)
– git-lfs push
– git-lfs status (status on just the LFS tracked files)
– bfg --convert-to-git-lfs '*.psd' --no-blob-protection

Migrate from SVN
• git svn clone http://svn.example.com/project/trunk
– Git svn fetch, git svn rebase
– Git svn dcommit
– Have a non-standard directory layout?
• https://git-scm.com/docs/git-svn

Migrate from Mercurial (hg)
• Hg fast-export plugin (seems to be the most
popular currently)
• hggit Mercurial plugin
• git-hg git plugin
• gitifyhg git plugin

Resources
• Cheat sheets
– https://training.github.com/kit/downloads/github-git-cheat-sheet.pdf
– http://www.git-tower.com/blog/git-cheat-sheet/
– https://www.atlassian.com/dms/wac/images/landing/git/atlassian_git_cheatsheet.pdf
– http://ndpsoftware.com/git-cheatsheet.html
• Recommended
– http://rogerdudler.github.io/git-guide/
– http://www.slideshare.net/lemiorhan/git-branching-
model?utm_source=slideshow&utm_medium=ssemail&utm_campaign=weekly_digest
– GitFlow: https://www.atlassian.com/git/tutorials/comparing-workflows/gitflow-workflow
– Worktree: https://github.com/blog/2042-git-2-5-including-multiple-worktrees-and-
triangular-workflows
– Submodules: https://git-scm.com/book/en/v2/Git-Tools-Submodules
• Git Clients
– http://sourcetreeapp.com/ (Mac/Windows GUI)
– http://gitextensions.github.io/ (Windows)
– https://github.com/dahlbyk/posh-git (PowerShell command line)
– http://www.git-tower.com/ (Mac client)

Resources II
• Git LFS
– https://git-lfs.github.com/
– http://www.sitepoint.com/versioning-large-files-with-git-lfs/
– https://help.github.com/articles/installing-git-large-file-storage/
– https://help.github.com/articles/about-git-large-file-storage/
– https://help.github.com/articles/configuring-git-large-file-storage/
– https://github.com/blog/1986-announcing-git-large-file-storage-lfs
– https://about.gitlab.com/2015/11/23/announcing-git-lfs-support-in-gitlab/
– http://stackoverflow.com/questions/33330771/git-lfs-this-exceeds-githubs-file-size-limit-of-
100-00-mb
• BFG
– https://help.github.com/articles/remove-sensitive-data/
– https://rtyley.github.io/bfg-repo-cleaner/
– http://blog.ctp.com/2014/04/15/cleaning-up-git-repositories-with-the-bfg-repo-cleaner/
– Git LFS support: https://github.com/rtyley/bfg-repo-cleaner/releases/tag/v1.12.5
• Filter Branch
– Filter branch stuff: https://multiplestates.wordpress.com/2015/03/04/reducing-the-size-of-a-
git-repository-by-removing-a-file-or-folder-from-its-history/

Kwen Peterson
• @kwenarik
• kwen.peterson@gmail.com
• https://github.com/Kwen/sfdevs
– These slides + Demo Examples

Common git branching strategy
• 3 core branches: master, dev, release
– Master is “the truth” and should always be in a stable,
fully-functional state. This is where new topic/feature
branches are cloned from. (nightly builds)
– Dev is where integration testing happens. This is
where topic branches are pushed and tested PRIOR
to being signed off on as stable enough to go to
master. (continuous integration, test environment)
– Release is where the last live build lives. This exists
so that if an absolutely critical issue arises, we can
make the fix here and release the build, being
confident that the ONLY change going out is the
critical bug fix.

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