Mastering git
Lesson 5
Irina Gulina Tomas Tomecek
How to find things?
Course grade: November 20
Course schedule
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Class N HW 2 3 4 5 6 Bonus Task
Deadline 11.10 18.10 25.10 1.11 8.11 13.11
Class 2 HW feedback
▸ I expected you’d fork into your own account namespace
･ Why creating new namespaces?
･ GitLab doesn’t have a way to connect a user with a fork in a namespace.
Local troubles
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Class 3 HW feedback
▸ Visualization (git log --graph is not great)
▸ Different levels of git experience in the class
▸ git pull vs. git pull --rebase
▸ Class 6 agenda
･ content of .git/ directory, read Git Internals:
https://git-scm.com/book/en/v2/Git-Internals-Plumbing-and-Porcelain
･ how does rebase work internally
･ difference in merge strategies, please read git-merge:
https://git-scm.com/docs/git-merge#_merge_strategies
･ git submodule
･ tig - terminal user interface for git
･ git aliases, shell aliases and shortcuts
Local troubles
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Today’s class
▸ How to show local commits which are not on origin remote?
▸ What is the difference between rebase and merge?
▸ What is the golden rule of rebase?
▸ What changes to commits can be done during an interactive rebase?
▸ What is a merge conflict? When/how does it happen?
▸ git switch main
git pull upstream main
git pull —rebase upstream main
What’s the difference between the two pull commands?
Questions
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Questions
Any questions or
suggestions?
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▸ Change working tree and HEAD (overflow from last class)
▸ git-reset
▸ Labs:
･ reset, restore, show
･ it’s never a bad idea to resolve some merge conflicts & rebase
Today’s class
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Local Troubles
Local troubles
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You have a great freedom
to rewrite your history locally
Git Cardinal Rule
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Change working tree and
HEAD
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⚠⚡DON’T LOSE YOUR WORK⚡⚠
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Steps to reproduce:
Do changes in working tree. “What did I do exactly? I don’t remember and want to know.”
✍ What exactly I changed? Or staged?
Solution:
$ git diff [<commit>] [--] [<path>...]
$ git diff --cached [<commit>] [--] [<path>...]
Typically you would want comparison with the latest commit,
so if you do not give <commit>, it defaults to HEAD.
Local troubles
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$ man git-diff
Steps to reproduce:
The cat walked across your keyboard, while you were making coffee. You have not noticed and saved
the changes in your editor, then saw them with git diff.
😸 Undoing local changes, not committed
Solution:
$ git restore -- <pathspec>
$ git checkout -- <pathspec>
git‐restore - Restore working tree files
pathspec - Pattern used to limit paths in Git commands.
Local troubles
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$ man git-restore man git-glossary
🛻 Changing the last local commit
1. How to modify the last commit message or add more stuff to the last commit
Solution:
$ git commit --amend
Don’t amend your last commit if you have already pushed it upstream!
Local troubles
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🔙 Undo the last local commit(s)
Solution:
$ git reset <last good commit>
$ man git-reset
git‐reset - Reset current HEAD to the specified state
--mixed Resets the index but not the working tree (i.e., the changed
files are preserved but not marked for commit) and reports what has not been
updated. This is the default action.
Local troubles
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🤯 Change HEAD into a known state
Solution:
$ git reset --hard <last good commit>
$ man git-reset
(--hard) set the current branch head (HEAD) to <commit>,
optionally modifying index and working tree to match.
Local troubles
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DISCARDS
UNSTAGED
CHANGES
󰠄How do I set my local main to upstream main?
Solution:
$ git reset --hard upstream/main
Local troubles
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󰞳Fix an earlier local commit
Scenario:
A file was not included in an earlier commit.
Solution:
$ git add <file>
$ git commit --fixup <earlier-commit>
$ git rebase -i --autosquash <even-more-earlier-commit>
Local troubles
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Moving local commits between branches
Scenario:
Commits were made on a main branch, but they should be on another branch instead
Solution:
$ git branch feature
What is the difference with git switch -c feature?
$ git reset --hard origin/main
$ git switch feature
How to avoid it?
Local troubles
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Public troubles
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Undo a commit, pushed
Steps to reproduce:
$ touch file.txt
$ git add file.txt
$ git commit -m “Something terribly wrong”
$ git push upstream main
Public troubles
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Undo a commit, pushed
Solution:
Find SHA hash of that commit.
$ git revert <commit>
$ git push
It’s the safest scenario, it doesn’t alter history!
Public troubles
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Local troubles - lab
Lab #1 Conflicts and Rebase.
▸ Pair with someone in a class to a group of two.
▸ Student #1 shares any git repo they have with a Student #2. It’s ok to share a Mastering git fork.
▸ Student #2 needs to create a PR to the repo of Student #1. Change an existing line, e.g. adding
their UCO to the beginning of any line in any file.
▸ After a PR is opened, Student #1 changes the same file and line too, e.g. by adding their UCO to the
end of a line.
▸ Now Student #2 needs to fix their PR, so it can be approved and merged. After merge, both UCO
should exist in that file.
▸ Mind meaningful commit messages, PR body and title, keep some short conversation in a PR.
Do the same changing the roles.
Labs
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THE END
Class 5 homework
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● Deadline: 8. November 2023, 23:59
● Pair with any student from your class. If you did a similar lab in a class, please switch roles and be Student
#1 or #2 accordingly.
● Student #1 shares any git repo (any “Example”, but not Mastering git) with Student #2 and Irina/Tomas.
● Student #2 makes a contribution to an existing file inside Student's #1 git repo by opening a MR.
● Student #1 will push a change to the repo ("Example") that will cause a merge conflict in Student's #2 MR.
● Student #2 resolves the merge conflict.
● After conflict is resolved, Student #1 asks to change something else in the MR. Based on a requested
change, Student #2 needs to do a rebase again or add an additional commit.
● MR should be merged in the end and or rejected/closed if no positive value.
● Afterwards, Student #1 makes any contribution to their own (“Example”) repo via MR, and Student #2
needs to process it accordingly.
● Both students shall mind/practise/demonstrate best Git practices on commits and MR.
● All MRs during this HW should also contain a file (in a separate commit) with a shell history. In a case of
rebase / new MR change, a new history file should be attached accordingly. So, in the end, each MR may
contain several commits demonstrating git history.
● In a case of any troubles tag us on a MR to help, or just share what difficulties you had in MR
conversations, so we can address the most common troubles on the last git class.
Class 5 homework
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https://gitlab.com/redhat/research/mastering-git/-/blob/
main/README.md#class-5-homework
Source: https://octodex.github.com/
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THE END
Questions?
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THE END
THANK YOU!
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