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class: center, middle, inverse

Git Internals

A brownbag workshop at

MX Technologies

by Seth House

@whiteinge
[email protected]

???

Bring your laptop, a bash shell, and install graphviz. Grab lunch downstairs then head up as soon as you can so we can start on time.

Topics (other topic requests welcome):

  • Branches.
  • Local and remote refs.
  • The reflog and garbage collection.
  • Visualize the DAG.
  • Rebasing and merge strategies.

Hands-on; Ask Questions!

--

  • brew install graphviz

  • apt-get install graphviz

--

  • Windows users may want something like wsl-open.

--

--

  • Wraps git rev-list <commit>.... --

  • Run git graph-dag without args to see usage.

    Can also be called directly. (chmod +x git-graph-dat)

--

  • Note, possible (likely, even) to generate multi-gigabyte images.

    • ctrl-c to abort.
    • Limit commit ranges.

Example

git graph-dag master~10..master origin/master~10..origin/master \
    | dot -Tpng \
    | open -a Preview -f

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Graphs & Pointers

Branches

--

  • find .git/refs

--

  • cat .git/refs/heads/master

--

  • less .git/packed-refs

Refs

  • Branches (local and remote).

  • Tags.

  • HEAD.

show

--

  • git show @{u}..

--

  • show --summary --stat --pretty=fuller --patch

--

  • printf 'foo\n' | git hash-object -w

Local and remote refs

  • git fetch --

  • git branch --set-upstream-to=origin/master

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Rebasing

Example

git init testrepo
cd testrepo
for commit in A B; do git stub $commit; done
git checkout -b feature HEAD~1
for commit in C D E; do git stub $commit; done

# git graph-dag master feature
# git rebase master
# git graph-dag master feature
# git graph-dag master feature <old-E-ref>

Interactive

git init testrepo
cd testrepo
for commit in A B C D E F G; do git stub $commit; done
git rebase -i HEAD~5

Reflog

  • git --no-pager reflog --date=relative
  • The reflog counts as a reference!
  • Persists for 90-days (default).

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Merging

Merge Conflicts

<<<<<<< HEAD
twas brillig, and the slithy toves
Did gyre and gimble in the wabe:
all mimsy were the borogoves,
And the mome raths outgrabe.
=======
'Twas brillig, and the slithy toves
Did gyre and gimble in the wabe:
All mimsy were the borogroves
And the mome raths outgabe.
>>>>>>> branchA

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Call to Action:
Experiment!