Git's hash-object command can be used to determine what hash id will be used by git when creating a blob in its internal file system.

$ echo 'Hello, world!' > hola
$ git hash-object hola
af5626b4a114abcb82d63db7c8082c3c4756e51b

When a commit happens, git will generate this digest (hash id) based on the contents of the file. The name and location of the file don't matter, just the contents. This is the magic of git. Anytime git needs to store a blob, it can quickly match against the hash id in order to avoid storing duplicate blobs.

Try it on your own machine, you don't even need to initialize a git repository to use git hash-object.

source