Strategies vs drivers

A merge strategy decides how Git combines two histories — ort (default since Git 2.34), recursive (legacy), resolve, octopus, and ours. A merge driver is per-file logic that runs when both sides have changed the same file. Choose the right tool for the right level.

Selecting a strategy

git merge -s ort feature
git merge -s ours legacy-branch
git merge -s octopus a b c d

ours records a merge but discards the other side's content — useful when retiring a branch you no longer want to integrate. octopus merges multiple branches at once but refuses if any conflict, suiting integration "ferry" branches.

Strategy options

Pass options with -X:

git merge -X theirs feature      # prefer feature on conflict
git merge -X ignore-all-space main
git merge -X renormalize legacy

renormalize applies clean/smudge filters before comparing, fixing merges across line-ending changes.

Custom drivers

Define a driver in .git/config or ~/.gitconfig:

[merge "ours-only"]
name = Always keep our version
driver = true

Wire it up in .gitattributes:

CHANGELOG.md merge=ours-only
*.lock merge=union

The built-in union driver concatenates both sides' lines instead of conflicting — perfect for append-only files like changelogs.

Real-world driver: yarn.lock

[merge "yarn-lock"]
name = Re-run yarn install
driver = "yarn install --silent && git add yarn.lock"

The driver receives the ancestor, ours, and theirs as arguments and must leave the merged content in the file at %A.

Driver contract

Driver scripts get placeholders: %O ancestor, %A ours (write result here), %B theirs, %P path, %L conflict marker size. Exit 0 for success, non-zero to leave a conflict for manual resolution.

Common mistakes

Forgetting that drivers must be installed on every clone — only .gitattributes is shared, not .git/config. Document setup in your README. Marking too many files merge=ours silently loses upstream fixes. Confusing the strategy -s ours (whole-merge) with the attribute merge=ours (per-file).

Related

See "Custom diff drivers with gitattributes", "Rerere: automatic conflict resolution reuse", and "Merge conflict resolution in depth".