Re: scripting the "rec" function for a fixed time.

[Eric <eric@cisu.net>]

On Wednesday 26 February 2003 04:19 am, Carl wrote:
> At 19:44 25/02/2003 -0500, Peter Howell wrote:
> >On Tue, 2003-02-25 at 01:14, pa3gcu wrote:
> >> > "rec" is not a stock linux command, and I cannot readily identify a
> >> > package that includes that application (just trying to match on "rec"
> >> > turns up several hundred hits in the Debian package database). So I'd
> >> > suggest you tell us a bit more about your setup, including enough
> >> > information that we can identify and take a look at the package that
> >> > includes this command.
> >>
> >> rec is an unix command altho' not well supported, slackware 8 has it
> >> included.
> >>
> >> rec --help shows a lot but thses are relavant to the question;
> >>   -c, --channels=CHANNELS      specifies the number of sound channels in
> >> FILE -d, --device=DEVICE          use DEVICE for input/output
> >>   -f, --format=FORMAT          specifies bit format of sample
> >>                                FORMAT is either s, u, U, A, a, or g
> >>   -r, --rate=RATE              sample rate in hertz of FILE
> >>   -s, --size=SIZE              interpret size of sample
> >>
> >> I think this one could be an help -s xxxxxxxb
> >>                                SIZE is either b, w, l, f, d, or D
> >
> >        Alas no :-(
> >        size isn't the file size.  It's really the width of each sample. 
> > eg b for 8 bits, w for 16 bits....
> >
> >It appears that rec does not buffer the sound, but instead writes it
> >directly to the file.
> >It's inelegant, but I suppose I could kill the application after a
> >specified delay.  There are two problems with implementing that for me.
> >Firstly, I don't think I could do that in perl, which I'm most familiar
> >with because there doesn't appear to be an easy way to spawn a process
> >and continue running the scipt.  Secondly, I don't know how to run a
> >process and get it's process id, which I'd need to kill it.
> >
> >        Ok, just did a little rtfm.  I guess I could use ps and extract
> > the id. Now I guess I'd better learn some bash scripting
>
> There is a tcl based interpreter called expect which lets you spawn
> processes and gives you it's pid easily. If you have any programming or
> scripting experience then it will be easy.
>
> Or there is a program called timelimit which is part of the netpipes
> package that spawns a process and kills it if it doesn't return after a
> specified time.
>
> I don't know how accurate these are and i have no experience of timelimit.

I am not sure if I am correct, but its worth a try:

If you are interested in scripting it I once had to do something similiar in 
BASH. By creating a function, it will execute the function commands in a 
subshell while continuing with the current script. Try something like this

#!/bin/bash
function boot ()
{
	*RecordProgram Command Here*&
}
boot 			#calls the funtion boot.
let PID = $!	#returns PID of last executed background command.
wait 9000  		#let it run for 9000 seconds
kill $PID

Something like that. this is opposed to the example below where the background 
ampersand will hang the script. If $! doesnt return the correct pid then you 
might be able to fake it using awk.grep and the ps command to isolate the pid 
column.

#!/bin/bash
Recordprogram&
letPID = $!
wait 9000
kill $PID

I believe the function wont hang the script waiting for input like the above 
example. Let me know if this sounds logical. I would appreciate input from 
any real bash programmers to see if I am correct. As always, best of luck!
#------------------------
#Eric Bambach   
#Eric@CISU.net 
#------------------------
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