I wrote a simple program to change settings on a matrix switch. If I just put single commands in it works but multiple commands don't. I am pretty sure the issue is lack of buffering in the matrix switch. There are no handshake lines. The switch echos the characters so I could check for each characters reply before sending - probably a better solution but delays seemed simpler and workable. (Now that I think about it seeing what is returned would be useful for debugging...) I have found some things on $| for I/O but none that are for the serial port so I don't know exactly how the code for that would be. I am a perl noob so mostly just following examples. Here is the code: 
#!/usr/bin/perl -w

# Controls HalfY matrix switch
# Switches both levels (audio and video)

use strict;

use Device::SerialPort; 

my $port = Device::SerialPort->new("/dev/ttyS0");

$port->baudrate(9600);
$port->parity("none");
$port->handshake("none");
$port->databits(8);
$port->stopbits(1);
$port->read_char_time(0);
$port->read_const_time(1);

# send data out
$port->write("CL1I1O1T");
print "TV input now from mythTV\n";
$port->write("CL2I1O1T");

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In reply to Disabling buffering of serial port? by JimLS

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