git show-index

Inspect what's inside a pack index.

🎯 What & why

git show-index dumps the contents of a packfile index (.idx) - object offset, SHA, and CRC for every object in the pack. It is pack forensics, nothing more.

🧠 Mental model

The .idx is a sorted lookup table into a .pack. show-index reads stdin and prints one line per object so you can see what is in there without rebuilding.

🛠️ Synopsis

git show-index [--object-format=<hash>] < <pack>.idx

Output (per line):
  <offset> <sha1> (<crc32>)

Note: reads the .idx on stdin, not as an argument.

🎚️ Switches & options

Flag	What it does
`< <pack>.idx`	Pipe the .idx file in via stdin (no positional arg)
`--object-format=<hash>`	Hash algorithm of the index: sha1 (default) or sha256

💡 Use cases

Confirm a specific object SHA lives in a particular pack.
Inspect the offset of an object for low-level debugging of corrupt packs.
Sanity-check a pack after manual transfer or repack.
Educational: see how Git lays out object indexes on disk.

🧪 Examples

List all objects in a pack

git show-index < .git/objects/pack/pack-abcd1234.idx

Find one object's offset

git show-index < .git/objects/pack/pack-abcd1234.idx | grep <sha>

Count objects in a pack

git show-index < .git/objects/pack/pack-abcd1234.idx | wc -l

SHA-256 repo

git show-index --object-format=sha256 < .git/objects/pack/pack-xxxx.idx

🎓 Recommendations

For most pack questions reach for git verify-pack -v first - it is friendlier and shows object types and sizes.
Use show-index when you need raw offsets or are debugging an index that verify-pack rejects.

🪤 Common pitfalls

It reads stdin, not a path argument - git show-index foo.idx will hang or error.
Output is offsets and SHAs only - no object types, sizes, or delta info (use verify-pack for those).
On sha256 repos you must pass --object-format=sha256 or the index will misparse.

🔗 Related modules

📝 Quiz

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