CommitHashes

CommitHashes are the unique identifiers assigned to commits in a version control history. They are generated by applying a cryptographic hash function to the commit's contents and metadata, producing a fixed-length string that serves as a fingerprint for that commit. The hash guarantees integrity: any change to the commit's tree, parent, author/committer data, or message changes the hash, effectively breaking references to the original commit.

In Git, each CommitHash is a 40-character hexadecimal string produced by the SHA-1 algorithm. The hash is computed from the commit object, which includes a snapshot of the project tree, a reference to the parent commit, and metadata such as author, committer, and timestamp. Because the hash encodes the entire history up to that commit, it serves as a content-addressable identifier for that state.

References to commits can use full or abbreviated hashes. Abbreviations are typically short (for example, the first seven characters) as long as they remain unambiguous within the repository. Common commands like git show, git log, and git rev-parse accept commit hashes as arguments.

Properties and considerations: commits form a directed acyclic graph via parent pointers; hashes are not guaranteed to be sequential or time-ordered, but they provide a stable way to refer to specific states. While SHA-1 is the traditional basis for Git's object IDs, workflows and future proposals discuss alternative hash algorithms; current mainstream Git deployments rely on 40-hex-character IDs.