AllExist check if all of the given files exist.

AtomicSymlink create symbolic link to src and overwrite tgt atomically if tgt exists.

CopyNoOverwrite copies source file to destination file.

CopySrcToFile copies the content from supplied reader to destination file.

DirectorySize walks a directory and returns its size in bytes.

DirExistsAndIsEmpty returns whether the given path is an existing directory, and exists.

Exists checks if the file under the given path exists by means of `stat()`.

NoneExists checks if none of the given files exist.

ResolveIfSymlink resolve path if it is a symlink, otherwise return path itself.