git unpack-file

Plumbing helpful in mergetool wrappers.

🎯 What & why

git unpack-file writes the contents of a single blob object to a temp file and prints the path. Plumbing glue used inside mergetool wrappers and diff drivers.

🧠 Mental model

Takes a blob SHA, dumps its raw bytes to a file named .merge_file_XXXXXX in the worktree, echoes the filename. That's the entire job - you clean up after.

🛠️ Synopsis

git unpack-file <blob>

🎚️ Switches & options

Flag	What it does
`<blob>`	Required positional: the SHA of a blob object to materialize.

💡 Use cases

Mergetool wrappers that need the BASE/LOCAL/REMOTE blobs as on-disk files.
Custom diff drivers that shell out to a tool expecting two file paths.
One-off inspection of a historical blob without touching the working tree's tracked file.
Scripts that compare blob contents byte-for-byte using external tooling.

🧪 Examples

Dump a blob to a temp file

git unpack-file 4b825dc642cb6eb9a060e54bf8d69288fbee4904

Use in a merge driver

BASE=$(git unpack-file $1); LOCAL=$(git unpack-file $2); REMOTE=$(git unpack-file $3)

Inspect then clean up

f=$(git unpack-file HEAD:README.md); less "$f"; rm "$f"

Compare two historical versions

diff $(git unpack-file HEAD:a.c) $(git unpack-file HEAD~5:a.c)

🎓 Recommendations

Always 'rm' the returned filename when you're done - unpack-file does not clean up.
Prefer 'git cat-file -p <blob>' when you only need stdout, not a file on disk.
Resolve symbolic refs to a blob SHA first (git rev-parse HEAD:path) before passing in.

🪤 Common pitfalls

The temp file lands in the current directory, not /tmp - watch out in clean working trees.
Leaks .merge_file_* files everywhere if your wrapper aborts before cleanup.
Argument must be a blob; passing a commit/tree SHA fails or does the wrong thing.

🔗 Related modules

📝 Quiz

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