use forks;
use forks::shared;

my $variable : shared;
$variable = "init";

my $thread = threads->new
    (sub {
     while() {
         sleep 1;
         print STDERR "\r", $variable;
     }
     });

while() {
    print STDERR " "x40, "Enter new value for \$variable: ";
    chomp($variable = <STDIN>);
}