"fatal: not a git repository (or any of the parent directories): .git"
to stderr and return 128 return code if not in a git work area.
--is-inside-work-tree
Returns true if inside a working tree, including the main working tree.
--show-prefix
When the command is invoked from a subdirectory, show the path of the current directory relative to the top-level directory. Works for both main work tree and linked trees. When in the root of the directory, produces empty string.
--show-toplevel
Show the absolute path of the top-level directory.
--show-cdup
When the command is invoked from a subdirectory, show the path of the top-level directory relative to the current directory (typically a sequence of "../", or an empty string).