See -validate => 'key', -ValidateCommand => sub { length( $_[0] ) <= 10 ? 1 : 0 } and the validation section of the Entry widget POD.

Thanks!!

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And find examples Tk validateCommand Help, Few doubts in perl-tk.

And that is only part one, part two/three/four/eleven is

widget - Demonstration of Perl/Tk widgets, Entries and Spin-boxes: 3. Validated entries and password fields.

Perl documentation documentation, Searching Perl Documentation, How to Read Perldocs

perl Tk help, RFC: Learning Perl/Tk, Perl/Tk: For Beginners, Re^3: Tkx Search for dialog box for text input , Re: TclTk interface with Perl code, is it possible? , Re^2: GUI toolkit+designer for the perl newbie , Re: Easier GUI, Re: Should I use Perl/TK?, Re^2: need a popup gui stdin, Tk Tree Tutorial ( http://www.rtapo.com/tutorials/tk_tree.html ), some Tkx tutorial links, Tutorial http://theoryx5.uwinnipeg.ca/perltk/ and http://www.perl.com/pub/1999/10/perltk/, http://perltk.org/, http://web.archive.org/web/20100310202528/http://theoryx5.uwinnipeg.ca/perltk/, How to RTFM Tk Tutorials

You are not alone :) see Tk::Button: How do I trigger a callback when button is pressed (as opposed to released)?

There are plenty of answers to be had at the speed of your fingertips

Thank you very much for your enthusiastic reply, the answer I need.