Why does git update-ref accepts non /refs references?

Question

While commands like \"git log\" will happily accept different expressions for the same ref, e.g.

refs/heads/master
heads/master
master

this is

Answer 1

tl;dr

The main reason why git log and git update-ref behave differently is because git-log is a high-level command – and therefore designed to be user-friendly – while git-update-ref is a low-level command meant to be used in scripts.

Porcelain vs. Plumbing

In Git parlance, high-level commands are referred to as porcelain while low-level ones are collectively called plumbing.

Porcelain commands are meant to be used interactively by humans and therefore expose familiar high-level concepts such as symbolic references. Plumbing commands, on the other hand, are meant to be used programmatically – usually in scripts – and allow to directly manipulate Git's internal file system structures.

git-update-ref

While git-log is able to resolve references, git-update-ref – it being a plumbing command – interprets the first argument as either a symlink or a regular file name depending on how it's specified.

From the documentation:

It follows real symlinks only if they start with "refs/": otherwise it will just try to read them and update them as a regular file.

So that's why if you say git update-ref master it will treat master as a file name and create it in the .git directory. By the same token, when you say git update-ref HEAD it will write to the .git/HEAD file.