How does the git diff –abbrev command work?

The git diff command is a tool that allows you to see changes between commits, commit and working tree, and so on. The --abbrev option used with the git diff command affects the length of the output SHA-1 values. It is mainly used when you want to reduce the length of the SHA-1 values that are usually printed out.

In Git, every commit is uniquely identified by a SHA-1 (Secure Hash Algorithm 1) hash. By default, this hash is a 40-character hexadecimal number. When looking at the diffs between two commits, this could become overwhelming. The --abbrev option helps make this easier on the eyes.

Here’s how it works:

git diff --abbrev=<n>

Where <n> is the number of hexadecimal characters you want the SHA-1 hash to be displayed as. The minimum number of characters is 4 and the maximum is 40, which is the full length of the SHA-1 hash.

For example, running git diff --abbrev=8 will result in the SHA-1 hashes being displayed as 8-character long strings in the diff output. If no <n> is provided, the default value is 7.

It’s important to note, however, that Git will potentially use more than <n> characters if it needs to ensure that the abbreviated SHA-1 value is unique across all objects (commits, blobs, trees) in your repository. This is because the --abbrev option provides a lower limit, not a strict limit.

Please note that this is mostly relevant when viewing raw diff formats, such as git diff-tree, git diff-files, etc. and not the human-readable git diff format, where the full commit hashes are typically not displayed.

Finally, keep in mind that --abbrev option doesn’t change the behavior of the diff output, but merely affects its readability by changing how the SHA-1 hashes are displayed.