git-merge-tree

Perform merge without touching index or working tree

TLDR

Preview merge result (modern mode, Git 2.38+)

$ git merge-tree [branch1] [branch2]

Perform a three-way merge with explicit base (deprecated mode)

$ git merge-tree [base] [branch1] [branch2]

Check for merge conflicts and show informational messages

$ git merge-tree --write-tree --messages [branch1] [branch2]

Check if a branch can be cleanly merged (exit code 0 = clean, 1 = conflicts)

$ git merge-tree --write-tree --no-messages [branch1] [branch2]

SYNOPSIS

git merge-tree [--write-tree] [options] branch1 branch2git merge-tree [--trivial-merge] base branch1 branch2

git merge-tree performs a three-way merge without touching the index or working tree. It shows what a merge would produce, making it useful for previewing merges or performing scripted merge analysis.The modern mode (default since Git 2.38) automatically finds the merge base, writes a result tree object, and reports conflicts. The exit code indicates success (0) or conflicts (1). This makes it ideal for CI pipelines and automation scripts that need to check mergeability without modifying any files.The deprecated trivial-merge mode requires specifying the base commit explicitly and only handles trivial merges.

PARAMETERS

BRANCH1

First branch to merge.

BRANCH2

Second branch to merge.

BASE

Common ancestor commit (deprecated trivial-merge mode only).

--write-tree

Modern mode (default since Git 2.38): automatically finds the merge base and writes a result tree object. Reports conflicts via exit code and stdout.

--trivial-merge

Deprecated mode: reads three trees and outputs trivial merge results. Requires explicit base.

--[no-]messages

Write informational messages such as "Auto-merging" and CONFLICT notices. Default: included when conflicts exist.

--name-only

In the output, show only filenames instead of full merge details.

--allow-unrelated-histories

Allow merging branches that share no common history.

--merge-base commit

Specify a merge base instead of computing one automatically. With this option, branch arguments can be trees instead of commits. Incompatible with --stdin.

--stdin

Read commits to merge from standard input, one pair per line. Implies -z.

-z

Use NUL characters as line terminators instead of newlines (for scripting).

CAVEATS

Plumbing command primarily intended for scripting. Output format differs between modern and deprecated modes. Modern mode requires Git 2.38 or later.