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sysopen(COM,COM1,O_RDWR) || die "Can't open COM1 $^E";

#code to send data to port
syswrite(COM,$string);  #sends $string to COM1
...
#code to read data from port
sysread(COM,$buf,$length);      #read $length bytes
$received = unpack("C*",$buf);  #unpack them