waitforusb is a utility that waits for a USB based serial device with a certain Vendor ID and Product ID to become available before executing another program.
For example waitforusb -vid 3007 -pid 9005 -- echo {} will wait for a USB serial device with the PID 9005 and VID 3007 before running echo {}. {} is replaced with the port name (i.e. /dev/ttyUSB1)