Git error "fatal: bad revision" when using git diff

Question

I am trying to show changes between the origin of a certain folder and I would like it to show only the names of those that were added and modified using the following command but it is returning an error.

Command:

git diff --name-only --relative --diff-filter AM origin -- foldername/

Error:

fatal: bad revision 'origin'

Why did that suddenly happen? How can I resolve it?

Edit

using a different repo and 'origin/master' only returns different results

C:\gitprojects\samplefolder (master -> origin)
λ git diff --name-only --relative --diff-filter AM origin/master
readme.md

C:\gitprojects\samplefolder (master -> origin)
λ git diff --name-only --relative --diff-filter AM master origin/master
readme.md

C:\gitprojects\samplefolder (master -> origin)
λ git diff --name-only --relative --diff-filter AM origin
Properties/sample.properties
readme.md

Answer 1

Have a look at the man page for git diff (run man git-diff).

In the Description section, you can identify the 4th variant for invoking git diff as the one you are using. The man page details its usage like this:

git diff [--options] <commit> [--] [<path>...]
    This form is to view the changes you have in your working tree relative to the named <commit>. You can
    use HEAD to compare it with the latest commit, or a branch name to compare with the tip of a different
    branch.

In your case, you are using the String origin as the <commit> (or revision) you want to compare your working tree to. This cannot work, because origin is not a revision/commit. That's what the error message is telling you.

origin is a "remote". A remote is just a reference to another remote clone of the repository and git diff cannot make comparisons between whole repositories, only between revisions/commits.

You can resolve this by specifying a commit you want to compare to. One example would be origin/master, meaning to compare to the tip of the master branch on the remote called origin. What commit to specify exactly depends on what you are trying to find out specifically.