Process watcher?

[DANZIG]

Hello All, I'm trying to write a script using TK and ran in to a problem.

I need to have the script running and watching a <FILE HANDLE> at the same time. The window is built useing a 'TEXT' widget. I'm wanting to have a file watched and when a NEW line appears in the <FILE> to have the new $_ displayed in the text box.

Any suggestions and or examples would be GREATLY appreciated. Below is what I'm working with now.

use Tk;
$input = text_in;
open INPUT, $input or die &quot;Cannot open $input for read :$!&quot;;

my $mw = MainWindow->new();


$mw->Label(-text => 'Members Listing:')->pack();
my $listbox = $mw->Scrolled('Listbox',
-width => 35,
-height => 5,
-scrollbars => 'e')->pack();

$listbox->insert('end', 'John Coltrane', 'Coleman Hawkins',
'Dexter Gordon', 'Charlie Parker', 'Lester Young',
'Ben Webster', 'Charlie Parker', 'Lester Young');


$mw->Label(-text => 'Message Out:')->pack();
my $text_out = $mw->Text(-width => 35,-height => 5)->pack();
my $text_out_box = $text_out->Scrolled('Text',
-width => 30,
-height => 5,
-scrollbars => 'e')->pack();



$mw->Label(-text => 'Message In:')->pack();

my $text_in = $mw->Text(-width => 35,-height =>5)->pack();
my $text_in_box = $text_in->Scrolled('Text',
-width => 30,
-height => 5,
-scrollbars => 'e')->pack();

my $bottom_frame = $mw->Frame()->pack(-side => 'bottom',-pady => 5);
$bottom_frame->Button(-text => 'Get Line',
-command => \&check)->pack(-side => 'left');


MainLoop;
$text_in->repeat(3000, &check);
sub check {
#chomp($line_in = <INPUT>);
$line_in = <INPUT>;
$text_in_box->configure(-state => 'normal');
$text_in_box->insert('end', $line_in);
$text_in_box->configure(-state => 'disabled');}




Thanks in Advance.

 

[hmerrill]

I believe what you are asking for is the same as a &quot;tail -f&quot; - here's what &quot;perldoc -q tail&quot; says:

How do I do a `tail -f' in perl?

First try

seek(GWFILE, 0, 1);

The statement `seek(GWFILE, 0, 1)' doesn't change the
current position, but it does clear the end-of-file
condition on the handle, so that the next <GWFILE> makes
Perl try again to read something.

If that doesn't work (it relies on features of your stdio
implementation), then you need something more like this:

for (; {
for ($curpos = tell(GWFILE); <GWFILE>; $curpos = tell(GWFILE))
{
# search for some stuff and put it into files
}
# sleep for a while
seek(GWFILE, $curpos, 0); # seek to where we had been
}

If this still doesn't work, look into the POSIX module.
POSIX defines the clearerr() method, which can remove the
end of file condition on a filehandle. The method: read
until end of file, clearerr(), read some more. Lather,
rinse, repeat.

There's also a File::Tail module from CPAN.

HTH.
Hardy Merrill
Mission Critical Linux, Inc.

http://www.missioncriticallinux.com

 

[DANZIG]

I don't think that will work the <FILE HANDEL> I'm using is actually a socket.

Perl Cook Book
File positions are only meaningful on regular files. Devices, pipes, and sockets have no file position.

Anything else that I could use?
I was looking at ev() but not sure as to weather it would work for what I'm wanting to do.

Any ideas, guidance, & or examples would be appreciated.