Windows 批次。 将串口数据放入变量中

Question

I have a hardware (battery controller) that send battery voltage over a serial port. It's just 4-digit value ('1232') every 5 seconds. I need to read that value and if it's below a treshold shut PC down. It's old WinXP machine where I'm allowed to use CMD only without creating temporary files.

On my home PC I created a test environment with two virtual ports (with com2com utility) and powershell script that emulates hardware:

cls
$port = New-Object System.IO.Ports.SerialPort
$port.PortName = "COM4"
$port.open()
while (1) {
$port.WriteLine("1000"+[char]13)
$port.close()
Start-Sleep -Seconds 5
$port.open()
}

Script below has to recieve data and shut down PC if value below treshold. But it doesn't work.

@ ECHO OFF
MODE COM5 BAUD=9600 PARITY=n DATA=8 > nul
set tr=1100
FOR /F "usebackq" %%i IN (`TYPE COM5`) DO set x=%%i
IF %x% lss %tr% (ECHO System will shutdown
rem shutdown /s
)

When I run script It's just waits endlessly.

Answer 1

The for /f loop does not output the results of the command line-by-line as received. It waits for the command to complete so, by using type COM5 you will have a running command that does not exit, unless it experiences EOF. To do this you can redirect its output as input to the for loop

<COM5 (for /L %%i in (0) do set x=%%i)

You have to note though that this will not run as a permanent loop and you'll have to create a permanent loop if you plan on running it continually.