[mythtv-users] Serial control of a TV

[David Brodbeck]

Yan Seiner wrote:
> George Nassas wrote:
>> On 14-Mar-09, at 2:11 AM, Greg Newton wrote:
>>
>>> I'd stick with the line-ends theory too - the manual for my LC46PD7X
>>> says "Eight ASCII codes + CR" - maybe try
>>>
>>> echo -e "POWR0  \r"
>>
>>
>> Not sure what the -e is doing but echo sends a newline (\n) after its 
>> output. The TV might be taking that newline as the start of its next 
>> command and, deciding it doesn't like it, ignoring everything until 
>> the next \r.
>>
>> The shell printf command doesn't send any extra characters so a printf 
>> "POWER0 \r" might do it for you and also leave the TV in a good state 
>> for the next command. echo -n works too if you're without printf.
> 
> -e enables parsing of special characters like '\r'.

If you're trying to send just a carriage return, you actually want to 
use both -e and -n.  Otherwise echo will still insert a newline on the end:

gull at dyna-soar:~$ echo -e "test.\r" | od -c
0000000   t   e   s   t   .  \r  \n
0000007
gull at dyna-soar:~$ echo -e -n "test.\r" | od -c
0000000   t   e   s   t   .  \r
0000006

It sort of depends on what the TV expects.  "\r \n" is a standard DOS 
end-of-line sequence, but to me "CR" would suggest just a carriage 
return, "\r".  UNIX uses "\n", a line feed, as its end of line character.