Springest devlunch: Git

Small in-company presentation about the internals of git and a simple use case that uses this knowledge.

Transcript

1. A gitty guide to Git Maarten Hoogendoorn maarten@springest.com March 1, 2013
2. About this talk 2/16
3. About this talk Bird’s eye view Accurate, but incomplete 2/16
4. Prior Knowledge Files (& directories) 3/16
5. Prior Knowledge Files (& directories) What Git Does Commits 3/16
6. You’ll learn about 1 Git internals Blobs Trees Commits Branches 2 Why should I care? 4/16
7. Blob This is a blob (Binary Large OBject) 5/16
8. Blob This is a blob (Binary Large OBject) It has a unique SHA (Secure Hash Algorithm) 5/16
9. Blob This is a blob (Binary Large OBject) It has a unique SHA (Secure Hash Algorithm) same blob ⇒ same SHA 5/16
10. Blob This is a blob (Binary Large OBject) It has a unique SHA (Secure Hash Algorithm) same blob ⇒ same SHA How does it look like? $ git hash-object Makefile 8384c7c4b3e1460c92f02c78a89c4467ba3c17e4 5/16
11. File system trees $ tree . |-- presentation.pdf |-- presentation.tex |-- figures | |-- blob.pdf | \-- springest.pdf |-- Makefile \-- settings.tex 6/16
12. File system trees $ tree . |-- presentation.pdf |-- presentation.tex |-- figures | |-- blob.pdf | \-- springest.pdf |-- Makefile \-- settings.tex Files Sub trees 6/16
13. Git trees File systems are trees We only have blobs 7/16
14. Git trees File systems are trees We only have blobs Time to build some trees! 7/16
15. Git trees File systems are trees We only have blobs Time to build some trees! $ git ls-tree HEAD 100644 blob 7055....eebf2890a42 presentation.tex 100644 blob e527....127c87f80b4 settings.tex 040000 tree f556....a1a42929a28 figures 100644 blob 2edd....f8b09467a29 Makefile 7/16
16. Git trees File systems are trees We only have blobs Time to build some trees! $ git ls-tree HEAD 100644 blob 7055....eebf2890a42 presentation.tex 100644 blob e527....127c87f80b4 settings.tex 040000 tree f556....a1a42929a28 figures 100644 blob 2edd....f8b09467a29 Makefile $ git rev-parse HEAD 9d8964533686208bbc54e9f2d3845884ccbb9f90 A tree is a ’blob’ too! 7/16
17. Where are we? 1 Git internals Blobs Trees Commits Branches 2 Why should I care? 8/16
18. Commits in a Picture master HEAD tree meta data 9/16
19. Commits in Git $ git cat-file commit 9d896453368...e9f2d3845884ccbb9f90 tree a92824742feb5c35c6c4ccbfa56439c16bae4aad author Maarten <maarten@moretea.nl> 1362089614 +0100 Initial version of CV 10/16
20. Commits in Git $ git cat-file commit 9d896453368...e9f2d3845884ccbb9f90 tree a92824742feb5c35c6c4ccbfa56439c16bae4aad author Maarten <maarten@moretea.nl> 1362089614 +0100 Initial version of CV $ git rev-parse HEAD 9d8964533686208bbc54e9f2d3845884ccbb9f90 Commit is a ’blob’ too! (Just like trees) 10/16
21. Branches $ git cat-file commit 9d896453368...e9f2d3845884ccbb9f90 tree a92824742feb5c35c6c4ccbfa56439c16bae4aad author Maarten <maarten@moretea.nl> 1362089614 +0100 (copied) 11/16
22. Branches $ git cat-file commit 9d896453368...e9f2d3845884ccbb9f90 tree a92824742feb5c35c6c4ccbfa56439c16bae4aad author Maarten <maarten@moretea.nl> 1362089614 +0100 (copied) 11/16
23. Branches $ git cat-file commit 9d896453368...e9f2d3845884ccbb9f90 tree a92824742feb5c35c6c4ccbfa56439c16bae4aad author Maarten <maarten@moretea.nl> 1362089614 +0100 (copied) $ git cat-file commit ‘git rev-parse HEAD‘ tree caf6e84ff8c195a339634b68786397b43ad00e1d parent 9d8964533686208bbc54e9f2d3845884ccbb9f90 author Maarten <maarten@moretea.nl> 1362093020 +0100 Fix some spelling mistakes 11/16
24. Branch names master foo bar 12/16
25. Branch names master foo bar $ ls .git/refs/heads master foo bar $ cat .git/refs/heads/master => ddf27254...2478b5e88b495 $ cat .git/refs/heads/foo => 770242f5...f14c69c7c514c $ cat .git/refs/heads/bar => ddf27254...2478b5e88b495 12/16
26. How Does This Help Me? Nice to know Basis for understanding git Understand merge Understand rebase 13/16
27. Merge master blue orange 14/16
28. Merge master blue orange master blue orange 14/16
29. Merge master blue orange master blue orange master blue orange merge commit 14/16
30. Rebase master blue orange 15/16
31. Rebase master blue orange master blue orange 15/16
32. Rebase master blue orange master blue orange master blue orange 15/16
33. Material Git from the bottom up (http://ftp.newartisans.com/pub/git.from.bottom.up.pdf) Pro git (http://git-scm.com/book) 16/16