Usually you just open the file, and as you loop thru it, insert each line into the text widget. I just slapped together this FORMAT, which is written to a string, then the string is inserted. What are you trying to do? Tail a file or something? Usually with the text widget, you use it's tags mechanism to format your lines. I think you are approaching the problem the wrong way, to put a format in a Tk Text widget.

#!/usr/bin/perl

my $foo = '';
open FH, '+>', \$foo or die $!;

format FH_TOP =
                   WHO COMMAND OUTPUT
USER        TERMINAL     DATE & TIME              LOCATION
-----------------------------------------------------------
.

my @who_output= `who`;

foreach my $line (@who_output) {
my ($userid,$terminal,$month,$day,$time,$location) = split(/\s+/,$line
+);
chomp $location;

format FH =
@<<<<<<<    @<<<<<<<<<  @<<< @<<  @<<<<<        @<<<<<<<<<<<<
$userid  $terminal  $month  $day   $time  $location
.
write FH;
}

#print "$foo\n";

use Tk;
my $top = new MainWindow;
my $txt = $top->Scrolled("Text")->pack;

 $txt->insert('end', "$foo\n") ;

MainLoop;
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but here is a way to tie stdout to the text widget, but usually you would setup a fileevent ( select ) on a filehandle, then in the fileevent's callback, you insert into the text widget, as you read them.

#!/usr/bin/perl
use warnings;
use strict;

use Tk;

my $mw = MainWindow->new();
my $tx = $mw->Text()->pack();

tie *STDOUT, 'Tk::Text', $tx;

$mw->repeat(1000, \&tick);

MainLoop;

my $count;
sub tick {
 ++$count;
 print "$count\n";
}
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