git mktree

Build a tree by hand from blob SHAs.

🎯 What & why

Plumbing that builds a tree object from a flat listing of entries on stdin and prints the resulting tree SHA. It is the inverse of ls-tree and the way to assemble trees without touching the index.

🧠 Mental model

Hand it the lines ls-tree would have printed and it gives you back a tree SHA. Combine with hash-object and commit-tree to fabricate a commit entirely server-side, with no working tree at all.

🛠️ Synopsis

git mktree [-z] [--missing] [--batch] < entries.in
# entry format per line:
#   <mode> SP <type> SP <sha> TAB <name>
# e.g. 100644 blob a1b2c3...\tREADME.md
# prints: <tree-sha>

🎚️ Switches & options

Flag	What it does
`-z`	NUL-terminate input records instead of LF (safe for weird filenames).
`--missing`	Allow referenced objects to be absent from the ODB.
`--batch`	Read multiple trees separated by blank lines; emit one SHA per tree.
`(stdin)`	Lines must be sorted as Git expects; otherwise the resulting tree differs.

💡 Use cases

Server-side commit fabrication: build a tree, then commit-tree, then update-ref.
Importers translating foreign snapshots into Git trees in bulk.
Scripted history rewrites that need a single altered tree without touching the index.
Teaching what ls-tree's output really represents inside the ODB.

🧪 Examples

Build a tiny tree by hand

printf '100644 blob %s\tREADME.md\n' "$(git hash-object -w README.md)" | git mktree

Round-trip an existing tree

git ls-tree HEAD | git mktree   # should reprint the same SHA as HEAD^{tree}

Batch-build many trees

cat trees.in | git mktree --batch    # blank lines separate trees

Tree -> commit -> ref, no working copy

tree=$(git ls-tree HEAD | git mktree) && c=$(echo msg | git commit-tree "$tree" -p HEAD) && git update-ref refs/heads/auto "$c"

🎓 Recommendations

Use ls-tree | mktree round-trips to verify your generator emits canonical entry order.
Prefer -z when filenames may contain spaces, tabs, or newlines.
Hash blobs with git hash-object -w first, or pass --missing if blobs land later.

🪤 Common pitfalls

Wrong sort order or duplicate names produce a tree with a different SHA than expected.
Mode strings must be exact (100644, 100755, 120000, 040000); 0644 is rejected.
Without --missing, referencing an object not yet in the ODB fails the command.

🔗 Related modules

📝 Quiz

Hit each option, then Check answers. Score is recorded; Next is always open.