Git concepts: commit

A Git commit, at its core, is a snapshot of your project's state at a certain point in time. But there's a lot more to it when we delve into the internals.

To fully understand what a git commit is, it's essential to know about the three main sections Git uses to function: the working directory, the staging area (or index), and the Git directory (repository).

When you make changes to your project, those changes are in your working directory. To track these changes, you need to add them to your staging area using the git add command. This process prepares your changes for a commit.

Now, when you run git commit, Git takes a snapshot of all changes in the staging area and stores this snapshot into the Git directory. This snapshot or commit is a unique object within the Git system.

Each commit is represented as a commit object in Git. The commit object contains the following:

A tree object that represents the top-level directory snapshot of the project. This tree object references other tree objects (directories) and blob objects (file contents). Metadata including the author's name and email, timestamp of the commit, and the commit message. SHA1 Hash: A unique 40 character identifier computed from the contents of the commit. This hash is the ID of the commit. Parent reference: Each commit (with the exception of the initial commit) also has a pointer to the commit or commits that came directly before it. This creates a chain of commits, or a lineage of history. The commit object does not contain a copy of the files in the project, but instead, references the exact state of these files at the time of the commit, hence creating an efficient system without duplicating contents.

Now, when you make another commit, the new commit will hold a pointer to the commit that came before it. Over time, commits form a linked list, a chain of history, if you will. This chain is what we refer to as a branch in Git.

In summary, a Git commit is a snapshot of your project files and directories that tracks changes over time. It is a complex construct that includes metadata, references to the project's state, and pointers to the previous commit(s), all uniquely identified by a SHA1 hash. This structure enables the powerful version control and branching capabilities that Git offers.