This is not a command the end user would want to run. Ever.
This documentation is meant for people who are studying the
Porcelain-ish scripts and/or are writing new ones.
The git sh-setup scriptlet is designed to be sourced (using
.) by other shell scripts to set up some variables pointing at
the normal Git directories and a few helper shell functions.
Before sourcing it, your script should set up a few variables;
USAGE (and LONG_USAGE, if any) is used to define the message
given by usage() shell function. SUBDIRECTORY_OK can be set
if the script can run from a subdirectory of the working tree
(some commands do not).
The scriptlet sets GIT_DIR and GIT_OBJECT_DIRECTORY shell
variables, but does not export them to the environment.