CIS241

System-Level Programming and Utilities

git (merging)

Erik Fredericks, frederer@gvsu.edu
Fall 2025

Based on material provided by Erin Carrier, Austin Ferguson, and Katherine Bowers

What is a merge conflict?

Merge conflict: when two commits compete

• People editing the same line
• File both edited and deleted

Resolving

Manually edit files and decide which to keep

Markers indicate who did what

• Between <<<<<<< and =======
  • local branch merging into
• Between ======= and >>>>>>>
  • remote branch being merged

Though, hard to read!

• Good use case for a visual diff program...

Regardless...

• Decide which to keep or combine in some way
• Replace with whatever decided
• Remove markers
• Repeat for all conflicts in each conflicting file
• Add files after resolving merge
• Run git commit

Resolving:

Q1: What if I just want to keep one version or the other, is there a better way?

• A1: Two options:
  • git restore --ours filename or git restore --theirs filename
  • Or, replace restore with checkout
    • ours = branch merging into
    • theirs = braanch being merged in

Resolving:

Q2: I screwed up the merge - can I start over?

• A2: git merge --abort
  • May delete any changes in working directory!!

Resolving

Q3: This is awful - is there another way?

• A3: Yes, but not the 'ideal' way
  • As before, pull down a "clean" copy of the repo into a new folder and merge your local changes into that
  • Then decide which folder to keep

Example of inducing a merge conflict

c/o reddit: https://www.reddit.com/r/git/comments/b3wm1j/how_to_best_intentionally_create_a_merge_conflict/

git init
echo 'Mr. Foo' > foo.txt
git add .
git commit -m 'foo'

echo 'Mr. Bar' > foo.txt
git add .
git commit -m 'bar'

# Branch from HEAD~1 - a.k.a. 1 commit ago.
git checkout HEAD~1
git checkout -b branch
echo 'Mr. Baz' > foo.txt
git add .
git commit -m 'baz'

git checkout master
git merge branch

Also, visualize:

git log --all --date-order --graph