use strict;
use warnings;

use Term::ReadKey;
$|++;  #you must autoflush buffer or it print only at newlines
ReadMode('cbreak');
print "How much is A:";
my $input;
my $char;
while ( $char = ReadKey(0) and $char =~/^\d$/ ){
	$input.=$char;
	print $char;
}
print " A=$input\n";