#!/usr/bin/perl
use strict;
use warnings;
use Tk;
require "./SFDTail.pm";
.
.
#  SFDTail.pm is our file handling package
my $tailer = SFDTail::new();
my $mw = MainWindow->new();
my $txtarea = $mw->Scrolled('Text', ... option stuff ...);
.
.
MainLoop;
.
.
#  grabtext() is our Tk::fileevent callback function
#  $tailer->fh() returns a file handle ($fh), created as:
#     open($fh, "tail -f -n 20 $self->{file} |");
sub grabtext
{
#  $stuff = <$tailer->fh()> don't work --??
 my $glob = $tailer->fh();
 my $stuff = <$glob>;
 $txtarea->insert('end', $stuff);
 $txtarea->yview('end');
}
.
.
#  Tk::Button event callback: select appropriate file, let $tailer open it.
#  $tailer->tail($file) is where the file gets opened, as above.
sub standard
{
 my $unit = shift;    # typically 'Unit01', 'Unit02', etc

#  clean up: close any previous filehandle and kill any tail PID's
 $tailer->closepipe();

 my $file = "/usr/local/scripts/tk/${unit}.txt";
 $txtarea->delete('1.0', 'end');

# if data input not active, the file may not be there
 if ( -f $file )
 {
  if ( $tailer->tail($file) )
  {
   $mw->fileevent($tailer->fh(), 'readable' => \&grabtext);
  }
 }
 else
 {
  $txtarea->insert('end', "\n No data for $unit. \n");
 }
}