Understanding Git

An unconventional Git workshop starts with thinking in "patch."

Transcript

1. Feb 6, 2018 Zhihao Yuan <zhihao.yuan@depaul.edu> Tanu Malik <tanu@cdm.depaul.edu> School of Computing College of Computing and Digital Media Understanding Git
2. To teach Git as a "better" SVN To teach Git as a version control system To teach Git rebase workflow There have been lots of Git tutorials…
3. Teaches Git in terms of "patch" This tutorial
4. Before we start Update your .gitconfig with some aliases which will be used during this workshop: https://goo.gl/Bgs5rN git clone https://github.com/lichray/nvi2/
5. git lg (customized log) git checkout git show git init (create repo) git status git add (stage file) git commit Basic Git
6. What is a patch A patch is a file, such that given a file A and a file B, a patch represents "changes" between A and B Let's consider A: common.h, B: common.h.new To generate a patch diff -u common.h common.h.new
7. + Added Lines '+++' = new file Line numbers '---' = old file An example of patch file - Deleted Lines <No symbol> Untouched Lines
8. Apply (patch < change7.diff) Undo (patch -R < change7.diff) Patch has two operations
9. Some styles for file naming in patch  --- v2.0.29/prog/README Mon Mar 10 15:13:12 1997 +++ v2.0.30/prog/README Mon Mar 17 14:58:22 1997  --- www/palemoon/distinfo (revision 454992) +++ www/palemoon/distinfo (working copy)  --- media/libcubeb/src/cubeb_sndio.c.orig 2017-01-12 17:53:15 UTC +++ media/libcubeb/src/cubeb_sndio.c  --- a/common/conv.c +++ b/common/conv.c
10. -p When you see the specified relative path under the current working directory, patch -p0 < some.patch When you want to strip the first component from the specified path, patch -p1 < some.patch
11. Examples  --- v2.0.29/prog/README Mon Mar 10 15:13:12 1997 +++ v2.0.30/prog/README Mon Mar 17 14:58:22 1997  --- www/palemoon/distinfo (revision 454992) +++ www/palemoon/distinfo (working copy)  --- media/libcubeb/src/cubeb_sndio.c.orig 2017-01-12 17:53:15 UTC +++ media/libcubeb/src/cubeb_sndio.c  --- a/common/conv.c +++ b/common/conv.c -p1 -p0
12. One patch that edits multiple files at the same time Two files Being diffed
13. Play with Git patches git show (commit as a patch) git diff (difference between commits as a patch) git apply -R git apply patch -p1 < some_git_style_patch.diff
14. Why do we need Git? What does this patch do? What are these numbers for? Where do I save this patch set? Can I evolve a software with just patches?
15. Problems Patches need to be documented Patches often need to be applied in order You don't want to save a patch set along with source code
16. Understanding "git commit" Each git commit command generates a documented patch Commits are sequentially arranged
17. In Git, can I apply two patches in a different order? Exchange? An output of git lg
18. In Git, can I apply two patches in a different order? Very often, you can git checkout -b new_branch # suggested git rebase -i 328d2f5 # before the range Manually exchange the two commits in editor
19. Additional operations while rebasing in an editor Merge two patches into one (fixup) Edit the commit message (reward) Edit the patch itself (edit) Delete a patch (drop) Same thing
20. Can I apply two patches in a different order? When you cannot, there is git mergetool
21. "But history should be immortal…" There is no "history", but only patch set
22. Understanding "branch" Branch is a named patch set "git push" is for sharing your patch set with others
23. Play with Git branches git branch (backup) git checkout -b (new branch) git checkout git push -u, git push
24. "How do I merge a branch into master?" Stop, you are doing it wrong Remember, patch set
25. How some folks think about merging master branch dev branch
26. When I think about merging  ∪
27. Problem to solve Make changes in branch available in branch
28. Methodology to take Turn branch into a superset of branch git checkout git rebase -i git checkout git merge # now in "fast-forward" mode
29. Alternatively git cherry-pick .. git cherry-pick <commit> Subcommands are as same as git rebase, e.g. -- continue & --abort.
30.  to view: git diff HEAD  to unstage: git discard  git commit Staged changes  to view: git diff  to stage: git add / add -u  to drop: "git checkout ." Unstaged changes A patch not yet committed
31. Frequently needed tasks Change last commit's message git commit --amend Fold the unstaged changes into the last commit git add -u git fix Checkout a branch with uncommitted changes
32. git stash (push) git stash pop git stash drop git stash show -p (as a patch) A stack of uncommitted patches Introducing git stash
33. Commit = patch Branch = patch set Stash = patch stack Summary
34. git reflog git reset, git reset --hard Worth to learn
35. Questions & Discussion