Very usefull. Thank you.

On 21 Mar 2018, 12:54 PM +0800, Radon Rosborough <radon.neon@gmail.com>, wrote:
How to get the list of commits which is included in master but not
in emacs-26? Is there a git command or a tool can output such a
list?

You want a list of commits, so refer to the manual page for
git-log(1). It says

The command takes options applicable to the git rev-list command to
control what is shown and how

so checking the "description" section of git-rev-list(1), we find

List commits that are reachable by following the parent links from
the given commit(s), but exclude commits that are reachable from the
one(s) given with a ^ in front of them.

and further,

A special notation "<commit1>..<commit2>" can be used as a
short-hand for "^'<commit1>' <commit2>".

The answer to your question is therefore

$ git log emacs-26..master