Controlling a RS-232 Serial Console from a Shell Script

Ishikawa · #1 (**permalink**) 01-10-2009

I'm using OpenBSD 4.4 and I have a power strip that can be controlled through a RS-232 serial console. It works great from cu and minicom but it doesn't support any way of controlling it programatically, just a console designed for humans. I want to be able to send commands and read the output of the commands through a shell script or some other program that can be called from a shell script. I'm not necessarily looking for solutions to the following problems I'm just looking for any way to make this work.

I looked into using a C program that interacts with the serial ports using termios.h, unistd.h and fnctl.h but it looks like I would be reinventing the wheel and doing tons more work than I need to.

I also tried using expect to control cu. This seems like the best way of doing it since expect is designed to interact with CLI's that were designed for humans. It works fine and turns things on and off until expect reaches a read statement following an expect statment. See the bottom code window.

An example of it working properly with cu:

Code:

# cu -l /dev/tty00 -s 9600
Connected


RPC-22 Series
(C) 2000 by BayTech
F1.10

Option(s) Installed:
True RMS Current

RPC-22>status
True RMS Current:   0.5 Amps
Maximum Detected:   0.7 Amps


 1)...Cable Modem     : On
 2)...Router          : On    Locked
 3)...Switch          : On    Locked
 4)...Outlet  4       : Off
 5)...Outlet  5       : Off
 6)...Outlet  6       : Off
 7)...Outlet  7       : Off
 8)...Outlet  8       : Off
 9)...Outlet  9       : Off
10)...Outlet 10       : Off
11)...Outlet 11       : Off
12)...Outlet 12       : Off

Type "Help" for a list of commands

RPC-22>on 4,5,6
RPC-22>status
True RMS Current:   0.4 Amps
Maximum Detected:   0.7 Amps


 1)...Cable Modem     : On
 2)...Router          : On    Locked
 3)...Switch          : On    Locked
 4)...Outlet  4       : On
 5)...Outlet  5       : On
 6)...Outlet  6       : On
 7)...Outlet  7       : Off
 8)...Outlet  8       : Off
 9)...Outlet  9       : Off
10)...Outlet 10       : Off
11)...Outlet 11       : Off
12)...Outlet 12       : Off

Type "Help" for a list of commands

RPC-22>

An example of it failing to work with expect controlling cu. This happens whenever a send statment is used after a expect statement:

Code:

# expect -d
expect version 5.43.0
argv[0] = expect  argv[1] = -d
set argc 0
set argv0 "expect"
set argv ""
expect1.1> spawn cu -l /dev/tty00 -s 9600
spawn cu -l /dev/tty00 -s 9600
parent: waiting for sync byte
parent: telling child to go ahead
parent: now unsynchronized from child
spawn: returns {1870}
1870
expect1.2> send "off 12\r\n"
send: sending "off 12\r\n" to { exp5 }
expect1.3> send "on 11\r\n"
send: sending "on 11\r\n" to { exp5 }
expect1.4> send "status\r\n"
send: sending "status\r\n" to { exp5 }
expect1.5> expect RPC-22>

expect: does "" (spawn_id exp5) match glob pattern "RPC-22>"? no
Connected


RPC-22 Series
(C) 2000 by BayTech
F1.10

Option(s) Installed:
True RMS Current

RPC-22>off 12
RPC-22>on 11
RPC-22>status
True RMS Current:   0.4 Amps
Maximum Detected:   0.7 Amps


 1)...Cable Modem     : On
 2)...Router          : On    Locked
 3)...Switch          : On    Locked
 4)...Outlet  4       : On
 5)...Outlet  5       : On
 6)...Outlet  6       : On
 7)...Outlet  7       : Off
 8)...Outlet  8       : Off
 9)...Outlet  9       : Off
10)...Outlet 10       : Off
11)...Outlet 11       : On
12)...Outlet 12       : Off

Type "Help" for a list of commands

RPC-22>
expect: does "Connected\r\n\r\n\nRPC-22 Series\r\n(C) 2000 by BayTech\r\nF1.10\r\n\nOption(s) Installed:\r\nTrue RMS Current\r\n\r\nRPC-22>off 12\r\r\nRPC-22>on 11\r\r\nRPC-22>status\r\r\nTrue RMS Current:   0.4 Amps\r\nMaximum Detected:   0.7 Amps\r\n\r\n\r\n 1)...Cable Modem     :expect1.6>
expect1.6> send "off 11\r\n"
send: sending "off 11\r\n" to { exp5 }
write() failed to write anything - will sleep(1) and retry...
expect1.7> write() failed to write anything - will sleep(1) and retry...
write() failed to write anything - will sleep(1) and retry...
write() failed to write anything - will sleep(1) and retry...
write() failed to write anything - will sleep(1) and retry...
write() failed to write anything - will sleep(1) and retry...
write() failed to write anything - will sleep(1) and retry...
write() failed to write anything - will sleep(1) and retry...
write() failed to write anything - will sleep(1) and retry...
write() failed to write anything - will sleep(1) and retry...
write() failed to write anything - will sleep(1) and retry...
^Cwrite() failed to write anything - will sleep(1) and retry...
sighandler: handling signal(2)
async event handler: Tcl_Eval(exit 130)
#

Perderabo · #2 (**permalink**) 01-10-2009

Well, the only problem I see is stuff like:
send "off 12\r\n"

That's not what type when you use cu manually, is it? You almost certainly type "off 12" and then hit the enter or carriage return key. So try just doing exactly what you type:
send "off 12\r"

I'm not sure that the extra \n characters are really the problem, but I'd give it a try.

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