DeviceStreams
DeviceStreams[device] gives a list of all open streams associated with a device.
DeviceStreams[device,patt] gives a list of streams whose names match the string pattern patt.
DeviceStreams[device,{patt1,patt2,…}] gives a list of streams whose names match any of the patti.
Please visit the official Wolfram Language Reference for more details and examples on core symbols.