You might want to look at the "editModified" flag of the text box. See Using Tk::Text and '<<Modified>>' or Tk::Text with Vi; Silly or not?

The problem with the <<Modified>> tag, is that it will only report the first letter, and can cause deep recursion errors, as shown here.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;
use Tk::Text;

my $MW = MainWindow->new(
    -title  => "Tk::Text test",
    -width  => 200,
    -height => 200
);
my $text = $MW->Text(
    -height => 10,
    -width  => 40,
    -wrap   => 'word'
);
$text->pack( -side => 'top', -fill => 'both' );
$text->bind( '<<Modified>>' => sub { 
                   getText( $text, @_ ); 
                   } );

$MW->Button(-text=>'Clear Modified Flag',
            -command => sub{  $text->editModified(0) }
            )->pack();

MainLoop;

sub getText {
    my ( $t, @args ) = @_;
    my $text = $t->get( '0.0', 'end' );

# will cause deep recursion error
#    $t->editModified(0);

    print "Got: $text\n";
    return if ( !$text );
    return 1;
}
[download]

#!/usr/bin/perl
use strict;
use warnings;
use Tk;
use Tk::TextUndo;

my $top = MainWindow->new;

my $text = $top->TextUndo->pack(
    -expand => 'yes',
    -fill   => 'both'
);

$text->bindtags( [ $text, ref($text), $text->toplevel, 'all' ] );

$text->bind( '<KeyPress>', [ \&callback, Ev('K') ] );

MainLoop;

sub callback {
    my ( $widget, $keysym ) = @_;

    print "\n$keysym key pressed";

    return
      if (
        (
                length($keysym) > 1
            and $keysym =~ /\p{Upper}/
            and $keysym !~ /Delete|BackSpace|Return|Tab/
        )
        or (    $keysym eq 'Delete'
            and $widget->index('insert') eq $widget->index('end -1c') 
+)
        or (    $keysym eq 'BackSpace'
            and $widget->index('insert') eq '1.0' )
      );

    print ' - text is edited.';
}
[download]

and a way to get current tags positions

#!/usr/bin/perl
use warnings;
use strict;
use Tk;
#subs borrowed from widget demo
my $usage = "USAGE: $0 filename searchstring (regexp|exact)\n";

my $mw = MainWindow->new( -bg => 'black' );
$mw->geometry('100x30+100+15');

my ($file_name, $search_string, $kind) = @ARGV;
if(! -e $file_name){print $usage; die "No file found $!\n"}
if($search_string eq ''){print $usage; die "Need a search string";}

my $file;
open (FH,"< $file_name");
read( FH,  $file, -s FH );
close FH;

$kind ||= 'exact';

my $text = $mw->Scrolled(qw/Text -setgrid true -scrollbars e/);
$text->tagConfigure( 'search',   -foreground => 'red',-background => '
+white' );

$text->insert('0.0', $file);
$text->mark(qw/set insert 0.0/);
$text->pack(qw/-expand yes -fill both/);

&search_text($text,\$search_string,'search',$kind);

MainLoop;

######################################################################
+#3

sub search_text {

    # The utility procedure below searches for all instances of a give
+n
    # string in a text widget and applies a given tag to each instance
+ found.
    # Arguments:
    #
    # w -    The window in which to search.  Must be a text widget.
    # string -    Reference to the string to search for.  The search i
+s done
    #           using exact matching only;  no special characters.
    # tag -    Tag to apply to each instance of a matching string.

    my ( $w, $string, $tag, $kind ) = @_;
    #print "@_\n";

    return unless ref($string) && length($$string);

    $w->tagRemove( $tag, qw/0.0 end/ );
    my ( $current, $length ) = ( '1.0', 0 );

    my ($current_last, $length_last);
    while (1) {
        $current =
          $w->search( -count => \$length, "-$kind", $$string, $current
+, 'end' );
        last if not $current;
        warn "Posn=$current count=$length\n",
          $w->tagAdd( $tag, $current, "$current + $length char" );
        $current = $w->index("$current + $length char");
    }

}    # end search_text
[download]

$txtBox->tagRanges('sel'); returns begin/end coordinates of selection in <x,y> 2D format and if I extract data from widget via get() method it will be 1D string. Is there simple method to convert coordinates to 1D?

$txtBox->tagRanges('sel'); doesn't return 2D coordinates, it returns the line.column of the selected text start and end point(s). If you get() the text between those endpoints, you will have the selected text.

my @ranges = $txtBox->tagRanges('sel');
my $text   = $txtBox->get(@ranges[0,1]);
[download]

When I select anything, I get error 'Tk::Error: wrong # args: should be ".frame1.text get index1 ?index2 ...?" at C:/Perl/lib/Tk.pm line 252'

Because you are not giving the get() method any indicies to work with. Try:

if(@r)
    {
        my $str = $txtBox->get(@r);
[download]

Note that @r may have more than two coordinates. You may need to test and allow for them.

...if I use 'delete', 'insert' (and other Tk::Entry commands)...

Be aware that Tk::Entry methods != Tk::Text methods for the most part. There are many similarities, but many differences too. Do you want to do this with a Tk::Text box or a Tk::Entry? It would probably be easier with the Tk::Entry, it doesn't already have a defined action bound to the Return key. Tk::Text does, so you'll have to try to figure out what action the user meant when they hit Return. Not impossible, but a larger can of worms than I would want to open.

That's exactly what I needed. Thanks!

From my point of view, type of control doesn't matter. Tk::Entry works fine.

#!/usr/local/bin/perl
use Tk;
use Tk ':variables';

use strict;
use warnings;

my @choices = qw/seeing something important reply reduction renowation
+ reconnaissance/;


# Main Window
my $mw = new MainWindow;

#GUI Building Area
my $frm_name = $mw -> Frame();

#Text Area
my $textarea = $mw -> Frame();
my $txt = $textarea -> Text(-width=>40, -height=>10);
my $srl_y = $textarea -> Scrollbar(-orient=>'v',-command=>[yview => $t
+xt]);
my $srl_x = $textarea -> Scrollbar(-orient=>'h',-command=>[xview => $t
+xt]);
$txt -> configure(-yscrollcommand=>['set', $srl_y], -xscrollcommand=>[
+'set',$srl_x]);

my $log = $textarea -> Text(-width=>40, -height=>2);

#Geometry Management
$frm_name -> grid(-row=>1,-column=>1,-columnspan=>2);

$txt -> grid(-row=>1,-column=>1);
$log -> grid(-row=>6,-column=>1);
$srl_y -> grid(-row=>1,-column=>2,-sticky=>"ns");
$srl_x -> grid(-row=>2,-column=>1,-sticky=>"ew");
$textarea -> grid(-row=>5,-column=>1,-columnspan=>2);

$txt->bind('<KeyPress>', [\&OnKeyPress, $txt]);

$txt->focus;

MainLoop;

sub OnKeyPress
{
    my $txtBox = $_[0];
    
    my $currentWord = $txtBox->get('insert -1c wordstart', 'insert');
    my $wordEnd = $txtBox->get('insert', 'insert -1c wordend');
    $log->delete('0.0', 'end');
    $log->insert('end', "wordEnd: <$currentWord, $wordEnd>");

    # do not want autocompletion in the middle of the word
    if(length $wordEnd == 0
    # want autocomplete only when typing, not on key up, down, enter, 
+etc.
    && $Tk::event->K =~/^[\w]$/)
    {
        for(@choices)
        {
            if(/^($currentWord)(.*)/)
            {
                my $theRest = $2;
                my $len = length $theRest;
                my $selFrom = $txtBox->index("insert");
                $txtBox->insert('insert', $theRest);
                $txtBox->tag('add', 'sel', "insert - $len chars", "ins
+ert");
                
                $log->insert('end', "matched: <$theRest>");
                last;
            }
        }
    }    
    
    return;
}
[download]

It took a while searching Google and testing variations of SelectFrom(), SelectTo(), tagging, etc. Until I found tag('add', 'sel', "insert - $len chars", "insert") in sources of Tk::SuperText and voila! I still don't know why this code doesn't work without '-1c', but it seems to be a good start for creating crystal ball.