git rev-list --oneline master ^origin/master 

Git rev-list will list commits in one branch that are not in another branch. It is a great tool when you're trying to figure out if code has been merged into a branch or not.

• Using the --oneline option will display the title of each commit.
• The ^ operator excludes commits in the specified branch from the list.
• You can pass more than two branches if you want. For example, git rev-list foo bar ^baz lists commits in foo and bar, but not baz.