git-show-index

Read an IDX file for a Git packfile and dump its contents to stdout

$ git show-index [path/to/file.idx]

$ git show-index --object-format [sha1|sha256] [path/to/file]

git-show-index < pack-index-file

pack-index-file
    The path to the binary pack index file (.idx) whose contents are to be displayed. This file is read from standard input (stdin).

The git-show-index command is a low-level plumbing command within Git, primarily used for inspecting the binary contents of a Git pack index file (.idx).

Pack index files accompany Git packfiles (.pack), which are highly compressed archives storing multiple Git objects (commits, trees, blobs, tags). The .idx file serves as an index, mapping object IDs (SHA-1 or SHA-256 hashes) to their respective offsets within the corresponding .pack file. This allows Git to quickly locate and decompress specific objects without scanning the entire packfile.

As a plumbing command, git-show-index is not intended for general daily use by end-users. Instead, it's a tool for Git developers, scripting, or debugging repository corruption or packfile issues. It reads the raw index data from standard input and typically outputs the SHA-1 or SHA-256 hashes of the objects contained within that index.

This is a plumbing command, meaning it's an internal tool primarily for Git's own operations or for developers debugging Git itself. It reads binary data from standard input and its output is typically just a list of object SHAs, which might require further processing for human readability or advanced analysis. It does not accept command-line options for filtering or formatting beyond what its internal logic provides.

The command expects the raw, binary content of a Git pack index file (.idx) to be piped to its standard input. For example, to inspect objects/pack/pack-<hash>.idx, you would typically use: cat objects/pack/pack-<hash>.idx | git-show-index or git-show-index < objects/pack/pack-<hash>.idx.

For each object listed in the provided pack index, git-show-index outputs its object ID (SHA-1 or SHA-256 hash) on a new line. The output is a plain list of hashes, suitable for piping to other commands or for programmatic processing.

The git-show-index command emerged early in Git's development, specifically around the time packfiles and their corresponding index files were introduced (roughly 2005-2006). Packfiles were a crucial innovation for Git, vastly improving storage efficiency and transfer performance by consolidating multiple objects into a single compressed file. As Git's internal data structures became more complex, tools like git-show-index became necessary for low-level inspection, debugging, and verification of these new formats. Its design as a simple stdin-to-stdout plumbing command reflects its role as a fundamental building block in Git's core toolkit.

git-pack-objects(1), git-verify-pack(1), git-cat-file(1), git-pack-check(1)