Hi Jon,
On Tuesday 12 March 2002 11:54 am, Jon Molin wrote:
> Gary Stainburn wrote:
> > Hi all,
> >
> > I've got a project where I need to develop an single-board-computer based
> > network device using packet modems connected to Amateur Radio equipment
> > and I'm trying to develop a simulator in Perl under Linux and I've got a
> > few questions.
> >
> > Basically I'm going to have X number of nodes running inside Xterm
> > sessions, all sitting in the same working directory and simulating
> > transmitting data by appending the data to a file. Each program will
> > simulate receiving the data, by doing the equivelent of a tail -f on this
> > file.
> >
> > Keyboard input will be used to simulate data being received from the
> > box's serial port.
> >
> > 1) How can I simulate the 'tail -f' under perl without hanging my
> > program.
>
> open (F, 'tail -f /var/log/messages |');
> while (<F>)
> {
> # do stuff
> }
> close (F);
>
This won't do because my code will hang on the file reading part of the
while(<F>) statement and prevent any further processing until some data is
available.
My program will be simultaniously handling incoming data from the radio (this
file) and a serial port (the keyboard) while processing real-time data that
has already been received.
> > If I pseudo code it it may give a better idea of what I mean.
> >
> > // in main code
> >
> > if ($command=&getcommand()) {
> > &do_something($command);
> > }
> >
> > sub getcommand() {
> > if character available
> > add character to buffer
> > if character = end.of.packet
> > return buffer
> > else
> > return false
> > }
> >
> > 2) can this same method be used to get the characters from the keyboard.
>
> read 'perldoc perlopentut', go to the part with pipes
Pipes are not really required here as I've already got a valid input stream
from the Xterm session - STDIN. All I need to do is to be able to check the
status of the stream, and if data is available then read it.
>
> > 3) can I reduce the priority of these programs (equivelent of the unix
> > 'nice' command) from within the perl script or do I need to do it from
> > the shell script calling the program. (If I nice -> xterm -> perl script,
> > will the nice still affect the perl script or will I have to do xterm ->
> > nice -> perl script)?
>
> open (F, 'nice -15 tail -f /var/log/messages |');
Surely, this will only reduce the priority of the nice command and not my
perl app?
>
> > 4) Is there an easy way (or a hard way) within Perl to control the xterm
> > output, something similar to GotoXY that I used to have in TurboPascal in
> > the good old (?) DOS days.
>
> i've never used dos (not even in the good old turbopascal days) but
> there are term modules:
> http://www.cpan.org/modules/by-module/Term/
> i bet they offer alot of control
I'll look into these, thanks.
>
>
> /Jon
>
> > --
> > Gary Stainburn
> >
> > This email does not contain private or confidential material as it
> > may be snooped on by interested government parties for unknown
> > and undisclosed purposes - Regulation of Investigatory Powers Act, 2000
> >
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--
Gary Stainburn
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