This presentation covers how to modify git history to fix mistakes and provide a clearer picture of the flow of changes. I walk through some basic git fundamentals, and then outline several different methods of modifying history, as well as what type of situation they would apply for.

1. “GIT-ING”
OUT OF
TROUBLE
H O W TO G O B A C K I N T I M E W I T H O U T E R A S I N G
Y O U R S E L F F R O M T H E F U T U R E

2. OUTLINE
• Basic Foundations of Git
• Fixes for Common Issues
• Other Useful Commands
• Recovering from
Catastrophic Failures

3. BASIC GIT
FOUNDATIONS
D O E S A N Y O N E R E A L LY G I T G E T ?

4. WHAT IS GIT ANYWAY?
Key-value data store
• Value: object being stored
• Key: SHA-1 hash of object

5. COMMIT
5 basic pieces of data
• Reference to top-level tree (folder) of snapshot
– Files/folders at the time of the commit
• Reference to parent commit
• Author with timestamp
• Committer with timestamp
• Commit message

6. FILE LOCATIONS IN GIT
• Working Directory
• Index (Staging Area)
• Repository
Working
Directory
Index
Repository
git add
git commit

7. FIXES FOR
COMMON
ISSUES

8. FIXING TYPOS/SMALL MISTAKES
• Typo in branch name
– git branch –m [new_name]
• Typo in your commit message
• Forgot to include a file
• Found a small bug after committing
– git commit --amend (--no-edit)
• Accidentally included changes
– git reset HEAD~1 (--soft)

9. ADDED TO WRONG BRANCH
• Need change from another branch
– git checkout [branch_to_add_to]
– git cherry-pick [commit_hash]
• Accidentally committed to `develop`
– git branch [new_name]
– git reset origin –hard
– git checkout [new_name]

10. CLEANING UP HISTORY BEFORE
PUSHING

11. CLEANING UP HISTORY BEFORE
PUSHING
• Use cases:
– Condense history
– Split commit
– Pretend things never happened
• Commands:
– git rebase –i origin

12. GOLDEN RULE OF REBASING
“Never rebase a shared branch.”
• Practical Golden Rule:
1. Determine the base commit
2. Do not rebase if anything past base commit is shared
B
A
D
C Pushed to
Origin

13. INTERACTIVE REBASE
Basic Syntax:
git rebase –i [<commit>]
Shows each commit ahead of the root commit and lets you decide what to do with them.
• Reorder commits
• Execute command against commit.
– pick: keep commit as-is
– drop: remove commit from history
– reword: keep contents of commit, but change message
– squash/fixup: amend previous commit with this one
– edit: pause rebase after commit to allow for amending
• git rebase –continue
– …

14. RECOVERING
FROM
CATASTROPHIC
FAILURE

15. Remember the Git
fundamentals
• When in doubt, just delete
everything and re-clone
• Noone can see your mistakes
if they no longer exist…
SO SOMETHING WENT
WRONG…

16. Remember the Git
fundamentals
• When in doubt, just delete
everything and re-clone
• Noone can see your mistakes
if they no longer exist…
SO SOMETHING WENT
WRONG…

17. Remember the Git
fundamentals
• Every commit is just an
object in the repository with
a hash
• Commits are read-only. You
cannot change a commit, you
can only create new ones.
SO SOMETHING WENT
WRONG…

18. GIT REFLOG
Basic Syntax:
git reflog [-n <number>]
• See entries in the “Reference Log”, along with their hashes
• You can reset a branch back to a “pre-catastrophic-
failure” hash

19. SUMMARY
H O W D O I R E M E M B E R A L L T H A T ?

20. CHEAT SHEET (FIXING COMMITS)
• Rename Branch
– git branch –m [new_name]
• Adjust previous commit
– git commit --amend --no-edit
• Copy commit from another branch
– git cherry-pick [commit]
• Accidental commits on `develop`
– git branch [new_branch]
– git reset origin --hard
– git checkout [new_branch]
• Clean up history
– git rebase –i origin
– move, fixup, squash, drop
• Split commit
– git rebase –I origin
– “edit”
– git reset HEAD~1
– Make new commits
– git rebase --continue
• Catastrophic failure
– git reflog
– get reset [some_commit_in_past]

21. CHEAT SHEET (USEFUL COMMANDS)
• Create new local branch
– git checkout –b [new_branch]
• Push locally created branch to BitBucket
– git push –u origin HEAD
• Update with latest from develop (add to end)
– git pull origin develop
• Update with latest from develop (add to beginning)
– git pull origin develop --rebase