We have used the 'git-lfs-pointer(1)' command historically to compare
varying implementation of the Git LFS protocol. This has been done by
passing both `--file` and `--stdin` to the command, which will in turn
compare the contents of both handles and return appropriately whether
they are the same or different.
One use case that Git LFS pointer does not yet support directly is
_checking_ to see whether a given file is a valid Git LFS pointer. This
is a different use-case than before, since we aren't doing any
comparison, we're simply checking whether the official implementation of
Git LFS can parse a given stream as a pointer.
As an aside, one way to do this today is the following:
$ git lfs clean < a.txt | git lfs pointer --stdin --file my.ptr
Where we first generate a pointer of the file 'a.txt' (via
`git-lfs-clean(1)`), and then redirect that to `git-lfs-pointer(1)`
against our own file.
Let's make this above incantation easier to execute by providing a
functionally equivalent `--check` option. Running `git lfs pointer
--check` (and passing either `--file`, or `--stdin`) will return either
1 or 0 depending on whether or not the given pointer file was invalid or
not.
This allows to create a pointer file by redirecting Stdout like
$ git lfs pointer --file=path/to/file > pointer-to-file
Before this change, "pointer-to-file" would also contain the line saying
"Git LFS pointer for path/to/file"
which makes the pointer file invalid.
