Playing with files on an Arduino with an SD card hooked to it. I can write a data file from the SD card to the monitor. Is there some way to write to a file through the monitor to a file on the host computer? Or a way to write one from the host back to the SD card?
You will need a program running on the PC that communicates with the Arduino - taking the place of the SerialMonitor program - and reading or writing to the PC disk.
If it is sending data to the Arduino there will need to be an Arduino program to receive the data and store it on the SD Card.
And vice-versa for sending data to the PC program.