How to get the serial port number in Makefile? - makefile

Question

Sometimes, you need to know the serial port number when developing MCUs. For example, I plug the USB cable of the board into the USB port of my computer, then one serial port number appeared in the Device Manager, such as COM6. Then I can use the programmer to upload my program (.elf or .hex) to the MCU, the premise is that I specify the serial port number, namely, the 6 in COM6, to the programmer through the command.
For example, in command prompt of CMD.exe, I use "dwdebug.exe com6,l
test.elf,qr" to flash the MCU, the dwdebug.exe is the executable program which used for programming, the com6 is the serial port number, and test.elf is the code to be flashed into the MCU, l means "load", qr means "quit dwdebug.exe after loading, and run mcu".
In addition, I can use the command "dwdebug.exe ls,q" to list all the serial port number available in CMD.exe, for example, after running dwdebug.exe ls,q in CMD.exe, the outputs displayed in the CMD window:
COM5 .Expecting break byte 0x00, but no bytes read.
ATmega328P on COM6 at 62537 baud.
Then I planed to write a Makefile, part of the Makefile is:
COM = 6
PRG = test
MCU_TARGET = atmega328p
CLK = 8000000UL
UPLOADER = dwdebug
flash:
dwdebug ls,q
$(UPLOADER) device com$(COM),l $(PRG).elf,qr
debug:
$(UPLOADER) device com$(COM),l $(PRG).elf
From the Makefile above we can see that the variable COM at the beginning of the Makefile must assigned by the user, the serial port number, namely, the value of COM, is used by dwdebug.exe for flashing and debugging.
So, I think it's better to extract the number "6" behind "ATmega328P on COM", and assigned it to the variable COM:
flash:
dwdebug ls,q
$(UPLOADER) device com$(COM),l $(PRG).elf,qr
debug:
$(UPLOADER) device com$(COM),l $(PRG).elf
The advantage of doing this is that the user no longer need to view the Device Manager, namely, the user will not assign the serial port number (the 6) to COM at the beginning of the Makefile too, let the code finish the work automatically.
After searching many web pages, now I can save the outputs of "dwdebug ls,q" in a .txt file, such as:
flash:
dwdebug ls,q > serial.txt
$(UPLOADER) device com$(COM),l $(PRG).elf,qr
Now, the content of serial.txt is:
COM5 .Expecting break byte 0x00, but no bytes read.
COM6 ................
ATmega328P on COM6 at 61934 baud.
But how to extract the number "6" behind "ATmega328P on COM", and use the "6" in Makefile as the value of variable COM? It is a difficult point that I cannot be overcome, is there anyway to overcome this problem?
Best regards.
P.S.1 "ATmega328P on COM" is not changed.
P.S.2 My OS is Windows 10
Extract the serial port number, and assigned it to a variable in Makefile.