None of the USBIP_* variables is required, and none changes the USB behaviour of a device - they turn on diagnostics, or tell the wrappers where to connect.

Variable	Read by	Default	Effect
`USBIP_PCAPNG`	`libusbip-device` and `libusbip-host` (and both wrappers)	unset - off	write every transfer to a PCAPNG capture file (Capturing traffic)
`USBIP_DEBUG`	`libusbip-device`	unset - off	log every control request (with the verdict) and every data transfer, to `stderr` (Debugging)
`USBIP_HOST`	the `libusb-1.0` / `libusbK` wrappers only	`127.0.0.1`	which USB/IP server to connect to
`USBIP_PORT`	the `libusb-1.0` / `libusbK` wrappers only	`3240`	its TCP port

These pages write their examples for a POSIX shell. Only the syntax differs:

	Linux / macOS (`sh`)	Windows `cmd`	PowerShell
for one command only	`USBIP_DEBUG=1 prog`	not supported	not supported
for the rest of the session	`export USBIP_DEBUG=1`	`set USBIP_DEBUG=1`	`$env:USBIP_DEBUG = "1"`
unset it again	`unset USBIP_DEBUG`	`set USBIP_DEBUG=`	`Remove-Item Env:USBIP_DEBUG`

Warning: In cmd, put each set on its own line: set USBIP_PORT=4000 && prog makes the space before && part of the value.

Substituting a wrapper for the system library is the one step that is not an environment variable on Windows:

	Linux	macOS	Windows
load the wrapper, not the system libusb	`LD_PRELOAD=/path/to/libusb-1.0.so.0`	`DYLD_LIBRARY_PATH` (SIP blocks `DYLD_INSERT_LIBRARIES`)	copy `libusb-1.0.dll` into the program's own directory, which Windows searches first
find your own shared library at run time	`LD_LIBRARY_PATH`	`DYLD_LIBRARY_PATH`	beside the `.exe`, or on `PATH`

pyusb needs neither: it takes the backend path as an argument.

Warning: USBIP_HOST / USBIP_PORT are not read by libusbip-host. A program using the host API picks its server in code, with usbip_host_set_transport() - the variables exist because a stock libusb or libusbK program has no place to pass one (see Wrappers). Both wrappers read them once, at libusb_init / UsbK_Init time - set them before the program starts.