How to get SHA of the latest commit from remote git repository?

Does anyone know how to get the latest SHA of a given branch from outside a git repository?

If you are inside a git repository, you can do:

git log origin/branch_X | head -1

However, I am not inside a git repository, and I would like to avoid having to clone a repository just to get the latest SHA of a tag/branch. Is there a clever way of doing this?

Use rev-parse

git rev-parse origin/master # to get the latest commit on the remote

git rev-parse HEAD          # to get the latest commit on the local 

If you want to check SHA-1 of given branch in remote repository, then your answer is correct:

$ git ls-remote <URL>

However if you are on the same filesystem simpler solution (not requiring to extract SHA-1 from output) would be simply:

$ git --git-dir=/path/to/repo/.git rev-parse origin/branch_X

See git(1) manpage for description of '--git-dir' option.