git unpack-objects

Reverse of pack-objects.

🎯 What & why

git unpack-objects reads a packfile from stdin and writes every contained object back out as a loose object under .git/objects/xx/. It is the literal inverse of pack-objects and is mostly a forensics tool when a pack or its index is suspect.

🧠 Mental model

Pack in, loose objects out. The command does not touch refs, the index, or the working tree; it only materialises blobs, trees, commits, and tags as individual files in the object store.

🛠️ Synopsis

git unpack-objects [-n] [-q] [-r] [--strict] < pack-*.pack
  # Note: pack is read from stdin, not given as an argument.
  # The matching .idx file is NOT used; the pack is decoded directly.

🎚️ Switches & options

Flag	What it does
`-n, --dry-run`	Parse the pack and report what would be unpacked; write nothing.
`-q, --quiet`	Suppress the progress meter.
`-r`	Recovery mode: keep going past broken/duplicate objects instead of aborting.
`--strict`	Run fsck-style checks on each object as it is written.
`--max-input-size=<n>`	Refuse packs larger than n bytes; useful when scripting against untrusted input.

💡 Use cases

Recover usable objects from a corrupt or partially downloaded pack.
Convert a small pack back to loose form so individual objects can be inspected with cat-file.
Forensics: see exactly which objects a pack would introduce before trusting it.
Bootstrap a fresh repo from a pack you received out of band (cat pack | git unpack-objects).

🧪 Examples

Dry-run a suspect pack

git unpack-objects -n --strict < /tmp/suspect.pack

Recover what you can from a broken pack

git unpack-objects -r < .git/objects/pack/pack-abc123.pack

Explode a pack into loose objects

cat pack-abc123.pack | git unpack-objects -q

Audit objects with strict fsck checks

git unpack-objects --strict < incoming.pack

🎓 Recommendations

Always start with -n --strict on an unknown pack before letting it write to your object store.
Run git gc afterwards if you exploded a large pack; loose objects are cheap to inspect but expensive to keep.
Pair with git index-pack when you want the inverse outcome (build an .idx without exploding).

🪤 Common pitfalls

Forgetting that the pack comes from stdin: passing the path as an argument silently does the wrong thing on some shells.
Exploding a huge pack can fill the filesystem with thousands of loose files; use -n first to size the impact.
Without --strict, a malformed object can be written to disk and only blow up later during fetch or fsck.

🔗 Related modules

📝 Quiz

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